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Mineral Concentrations of Cool Season Pasture Forages in North Florida during the Winter-Spring Grazing Season

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Mineral Concentrations of Cool Season Pasture Forages in North Florida during the Winter-Spring Grazing Season
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CHELLIAH, GUNASEGARAN
Copyright Date:
2008

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Animals ( jstor )
Beef cattle ( jstor )
Cattle ( jstor )
Forage ( jstor )
Grazing ( jstor )
Liver ( jstor )
Minerals ( jstor )
Pastures ( jstor )
Plasmas ( jstor )
Seasons ( jstor )
City of Gainesville ( local )

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University of Florida
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University of Florida
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Copyright Gunasegaran Chelliah. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
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5/31/2007
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658216454 ( OCLC )

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MINERAL CONCENTRATIONS OF CO OL SEASON PASTURE FORAGES IN NORTH FLORIDA DURING THE WI NTER-SPRING GRAZING SEASON By GUNASEGARAN CHELLIAH A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2006

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Copyright 2006 by Gunasegaran Chelliah

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To my father-in-law, Dr. Muthuswamy Subbuswamy. B.E., M.S., Ph.D. and To my heavenly parents and great uncle, Dr. M. C. Chellam. GMVC, FRCVS. for their blessings

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iv ACKNOWLEDGMENTS The author wishes to express his appreci ation and gratitude to Dr. Robert Myer, chairman of the supervisory committee, for his valuable guidance and assistance throughout the research program as well as in the preparation of this manuscript. Special appreciation and thanks are expressed to Dr. Lee R. McDowell, cochairman of the committee, for his wisdom and friendship and fo r mentoring the author during his days in graduate school. Acknowledgements are also due to Dr. Jeff Carter for his time and advice as a committee member. Recognition and appreciation are due to Mrs. Nancy Wilkinson for her “patience” and assistance in all laboratory work and to Ms. Meghan Brennan and Dr. Ramon Littell for their assistance in the statistical analys es. The cooperation of Harvey Standland and NFREC Beef Unit and forage program personne l for all help in sample collection is gratefully recognized. Special thanks are due to Mr. Michael Miya ttai for his timely assistance in preparati on of thesis work. The author is especially grateful to hi s parents-in-law, Dr. S. Muthuswamy and Mrs. Karpagam Chellam, for their love, moral and financial support. Finally, he wishes to express his most sincere appreciation to his wife Saishree Muthuswamy, sister-in-law Padmalakshmi Mu thuswamy, his son Saiprassad G., and his daughter Saikrishnapriya G., for their suppor t, understanding and encouragement to accomplish his endeavor.

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v TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iv LIST OF TABLES...........................................................................................................viii ABSTRACT....................................................................................................................... ..x CHAPTER 1 INTRODUCTION........................................................................................................1 2 LITERATURE REVIEW.............................................................................................4 The Role of Macro-minerals in Beef Cattle.................................................................5 Calcium..................................................................................................................5 Phosphorus............................................................................................................6 Potassium...............................................................................................................8 Sodium and Chlorine...........................................................................................10 Magnesium..........................................................................................................11 Sulfur...................................................................................................................13 The Role of Microminerals in Beef Cattle.................................................................14 Copper.................................................................................................................15 Iron......................................................................................................................17 Zinc......................................................................................................................19 Manganese...........................................................................................................21 Cobalt..................................................................................................................23 Molybdenum........................................................................................................24 Selenium..............................................................................................................25 Mineral Composition of Forages................................................................................27 Forage Macrominerals.........................................................................................29 Calcium and Phosphorus..............................................................................29 Magnesium...................................................................................................31 Potassium.....................................................................................................32 Sodium and Chlorine....................................................................................33 Sulfur............................................................................................................34 Forage Microminerals.........................................................................................35 Copper..........................................................................................................35 Iron...............................................................................................................36 Zinc...............................................................................................................37

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vi Manganese....................................................................................................38 Cobalt...........................................................................................................39 Molybdenum................................................................................................40 Selenium.......................................................................................................41 Liver Minerals............................................................................................................42 Copper.................................................................................................................42 Iron......................................................................................................................43 Manganese...........................................................................................................44 Cobalt..................................................................................................................44 Molybdenum........................................................................................................45 Selenium..............................................................................................................46 Blood Plasma Minerals...............................................................................................46 Calcium and Phosphorus.....................................................................................47 Magnesium..........................................................................................................48 Copper.................................................................................................................49 Iron......................................................................................................................50 Zinc......................................................................................................................51 Selenium..............................................................................................................52 Mineral Status of Soils................................................................................................52 Macrominerals.....................................................................................................54 Trace minerals.....................................................................................................56 3 MATERIALS AND METHODS...............................................................................59 4 MINERAL CONCENTRATIONS OF COOL SEASON PASTURE FORAGES IN NORTH FLORIDA DURING THE WINTER -SPRING GRAZING SEASON: . MACROMINERALS AND FORAGE ORGANIC CONSTITUENTS.................67 Introduction.................................................................................................................67 Materials and Methods...............................................................................................68 Results and Discussion...............................................................................................73 Forage minerals...................................................................................................73 Study 1..........................................................................................................73 Study 2..........................................................................................................78 Blood plasma minerals........................................................................................82 Summary.....................................................................................................................83 Implications................................................................................................................84 5 MINERAL CONCENTRATIONS OF COOL SEASON PASTURE FORAGES IN NORTH FLORIDA DURING WI NTER-SPRING GRAZING SEASON: II. TRACE MINERALS.............................................................................................94 Introduction.................................................................................................................94 Materials and Methods...............................................................................................95 Results and Discussion...............................................................................................98 Forage trace minerals..........................................................................................98 Study 1..........................................................................................................98

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vii Study 2........................................................................................................101 Liver trace minerals....................................................................................104 Blood plasma trace minerals......................................................................105 Summary...................................................................................................................106 Implications..............................................................................................................107 6 SUMMARY AND CONCLUSION.........................................................................116 LIST OF REFERENCES.................................................................................................120 BIOGRAPHICAL SKETCH...........................................................................................144

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viii LIST OF TABLES Table page 3-1 Analysis performed on collected samples; Studies 1 and 2.....................................64 4-1 Forage macromineral concentrations in Studies 1 and 2; le vel of significance.......86 4-2 Forage macromineral concentrations (%, DM) during winter-spring grazing season; Study 1.........................................................................................................87 4-3 Forage macromineral (Ca, P) con centrations (%, DM) during winter-spring grazing season; Study 2............................................................................................88 4-4 Forage macromineral (Na, K, Mg) co ncentrations (%, DM) during winter-spring grazing season; Study 2............................................................................................89 4-5 Forage dry matter (DM), in vitro or ganic matter digestibility (IVOMD), and crude protein (CP) in Studies 1 and 2; level of significance....................................90 4-6 Forage dry matter (DM) yield (kg/ha), in vitro organic matter digestibility (IVOMD; %, DM) and crude protein (CP; %, DM) during winter-spring grazing season; Study 1.........................................................................................................91 4-7 Forage dry matter (DM) yield (kg/ha), in vitro organic matter digestibility (IVOMD; %, DM), and crude protein (C P; %, DM) during winter-spring grazing season; Study 2.........................................................................................................92 4-8 Plasma macromineral concentrations in beef cattle during winter-spring grazing season of the second year of Study 2; level of significance.....................................93 4-9 Plasma macromineral concentrations (ppm) in beef cattle during winter-spring grazing season of the second year of Study 2..........................................................93 5-1 Forage trace mineral con centrations in studies 1 a nd 2; level of significance.......108 5-2 Forage trace mineral (Cu, Fe, Zn, Mn ) concentrations (ppm of DM) during winter-spring grazi ng season; Study 1...................................................................109 5-3 Forage trace mineral (C o, Mo, Se) concentrations (ppm of DM) during winterspring grazing season; Study 1...............................................................................110

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ix 5-4 Forage trace mineral (C u, Fe, & Zn) concentrations (ppm of DM) during winterspring grazing season; Study 2...............................................................................111 5-5 Forage trace mineral (M n, Co, Mo, & Se) concentrations (ppm of DM) during winter-spring grazi ng season; Study 2...................................................................112 5-6 Liver trace mineral concentrations in beef cattle during winter-spring grazing season of the second year of Study 2; level of significance...................................113 5-7 Liver trace mineral concentrations (ppm of DM) in beef cattle during winterspring grazing season of the second year of Study 2.............................................114 5-8 Plasma trace mineral concentrations in beef cattle during winter-spring grazing season of the second year of Study 2; level of significance...................................115 5-9 Plasma trace mineral concentrations (ppm) in beef cattle during winter-spring grazing season of the second year of Study 2........................................................115

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x Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science MINERAL CONCENTRATIONS OF CO OL SEASON PASTURE FORAGES IN NORTH FLORIDA DURING THE WI NTER-SPRING GRAZING SEASON By GUNASEGARAN CHELLIAH May 2006 Chair: Robert O. Myer Cochair: Lee R McDowell Major Department: Animal Sciences Two experimental cool season grazing st udies (Study 1 and 2), each lasting two years, were conducted at the North Florida Research and Educati on Center, Marianna, Florida, to evaluate the mineral concentra tions of cool season pasture forages grazed by growing beef cattle over four consecutiv e winter grazing seasons (2001-2005). Growing steers and heifers grazed on two different types of pastures (sod-seeded vs. clean tilled) with two different forage combinations: sma ll grains (rye/oats mix) with or without ryegrass for the first two years (Study 1), a nd oats with ryegrass or ryegrass only for the last two years (Study 2). Mine ral concentrations in blood pl asma and liver collected in the spring of 2005 from the tester beef cattle we re also evaluated to determine the mineral status. Cattle received a complete minera l mixture while grazing the experimental pastures.

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xi In Study 1, forage concentrations of macr ominerals Ca, P, K, and Mg were all adequate and higher than the cr itical dietary levels recommended for growing beef cattle. But in Study 2, Ca and Mg concentrations were below critical concen trations in forages for almost all months of the winter-spring gr azing season. Forage Na concentrations were consistently low and unaffected by either fora ge type or pasture t ype (land preparation methods) used in both studies. This latter st udy indicated that the low forage Mg with high K may be a potential for Mg deficiency in grazing beef animals since Mg absorption is considerably depressed by high dietary K. All tester cattle from all treatments had normal plasma Ca and P concentrations with only slightly depressed Mg levels. High forage crude protein and in vi tro organic matter digestibility concentrations declined at the end of the grazing season in both studies. Individual trace mineral concentrations in forage samples were highly variable in both studies. Pasture type (la nd preparation method) had a significant effect on forage Cu, Zn, Mn, and Mo concentrations. All forages were Cu deficient in Studies 1 and 2. In Study 1, forage Mn concentrations were genera lly above dietary critic al levels while Co and Se concentrations were deficient. In Study 2, differences betw een two pasture types existed in forage concentrations of Fe, Zn, Co, and Mo. Selenium forage concentrations were low and showed no difference (P>0.05) due to pasture forage combinations. Based on liver and plasma concentrations, growing an imals had a normal status for Cu, Fe, Co, Se, and Zn but low concentrations of Mn and Mo. Land preparation methods and forage types had no effect (P>0.05) on forage mine ral concentrations. Since pasture forages contained low concentrations of Ca, Na, Cu, Se, and Mg, supplementation of these minerals is needed for growing beef cattle.

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1 CHAPTER 1 INTRODUCTION Annual cool season pasture forages are th e foundation of pastures during winterspring grazing season in North Florida. The plan ting of cool season annuals such as rye, oats, and/or ryegrass, to provi de forage for grazing by beef cattle during the late fall to spring period is commonly practiced in the southern coastal plain region of the USA. Forage quality and quantity of pastures is extremely important when feeding programs targeting the maximization of animal produc tion are to be designed for beef cattle (McDowell, 2003). Mineral concen trations in plants generally reflect the adequacy with which the soil can supply absorbable mineral to their roots. One r eason for the existence of mineral deficiencies in grazing animals, such as calcium, phosphorus, sodium, copper, cobalt and selenium, is that the soils of the particular areas are i nherently low in plant available supplies of these minera ls (Underwood and Suttle, 1999). Feeding the required nutrients to the animal is important for sustaining normal health, optimum metabolic functions and animal productivity. Adequate intake of feed by animals and supplementation of minerals in sufficient concentrati ons are essential in meeting mineral requirements. Factors, which greatly reduce forage intake, such as low protein (<7.0%) content and increased degree of lignifications, likewise reduce the total minerals consumed by grazing animals. Mine ral requirements are highly dependent on the level of cattle productivity and are affect ed by many factors including kind and level of production, age, level and ch emical form of elements, in terrelationships with other minerals, mineral intake, and breed a nd animal adaptation (McDowell, 2003).

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2 Maintenance, growth, lactation, reproduction and animal health cannot be optimized where mineral intake is not properly balanced. Mineral deficiencies and imbalances for grazing livestock are re ported from almost all world regions (McDowell, 2003). Phosphor us, Ca, and Na probably represent the macrominerals most commonly deficient in tropical areas (Khali li et al., 1991). Trace minerals that have been identified as impor tant for normal immune function and disease resistance include zinc, iron, copper, manganese and selenium (Fletcher et al . , 1988). A deficiency in one or more of these elemen ts can compromise immunocompetence of an animal (Beisel, 1982; Suttle and Jones, 1989). Reproductive performance of cattle may be compromised if zinc, copper, or manganese status is in the marginal to deficient range. Common copper deficiency si gns in cattle include dela yed or suppressed estrus, decreased conception, infertil ity and embryo death (Phillip po et al., 1987; Corah and Ives, 1991). When cattle rely mainly on forages to meet their nutritional needs it is important to analyze the factors that may affect forage quality and quantity to design management programs that will improve animal performa nce and eliminate nutritional deficiencies. Among those factors are soil pH, mineral c oncentration in soil , and plant nutrient composition (protein, energy, minerals and vitami ns). It is important to determine mineral concentrations of soils, forages, and animal tissues to estimate the mineral needs of grazing ruminants as well as the time of year when they are most required. Evaluation of the mineral status of grazing ruminants, incl uding analyses of soil, forages, and animal tissues, helps identify minerals most likely limiting cattle production. Forage testing is the foundation for understanding the existing mine ral status and establishing the need for

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3 and the amount of supplemental minerals. Soil testing can help explain forage composition, but is not reliable in directly ev aluating the mineral status of the animal. Likewise, blood testing and liver analyses can add information on a herdÂ’s mineral status (Mills, 1987). Langlands (1987) indicated that tissues and blood are more reliable means of evaluating mineral status of grazing ruminants than forages due to soil contamination or variability in diet selection or availability of ingested nutrients or mineral supplements. Keeping the above considerations in mind, two experimental winter grazing studies were conducted to assess the mineral concentr ations of cool season pasture forages in North Florida over a period of f our years. In addition, forage s were evaluated for protein content and digestibility characteristics. Gr azing beef cattle were monitored for growth and general health. Plasma and liver samples were collected and analyzed to determine the mineral status in th e grazing animals.

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4 CHAPTER 2 LITERATURE REVIEW Minerals available in the forages play si gnificant roles in beef cattle production, as minerals serve many diverse but essential functions in the animalÂ’s body such as regulation of muscle contra ction, blood coagulation, nerve transmission and osmotic balance. Understanding the fact ors such as the livestock mi neral requirements, functions of each mineral and mineral concentration in the animal feed that result in deficiencies or toxicities is necessa ry to maintain beef cattle at high levels of production. Serious deficiency diseases can deve lop without these elements in adequate amounts even though the total mineral content of the animalÂ’s body is usually less than 5%. Mineral deficiencies and imbalances are reflected in poor animal condition, increased death losses and poor productivity. Identifica tion of what minerals are deficient, when they are deficient and the severity of deficiencies are major concerns of livestock producers depending primarily on forages for animal feeding. There are at least 17 mineral elements c onsidered essential an d listed as dietary requirements for maintaining health and productiv ity of beef cattle, according to the 2000 Beef cattle NRC. Mineral requirements of b eef cattle can be categorically grouped into the macrominerals and the micromineral s or trace elements. Macrominerals are quantitatively distinguished fr om the trace elements in th at they are required by or represented in the animalÂ’s body in relati vely large amounts. Calcium (Ca), phosphorus (P), potassium (K), magnesium (Mg), sodium (Na), chloride (Cl), a nd sulfur (S) are the important macrominerals essentially required by ruminants. Cohen (1987) concluded that

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5 adequate macrominerals in the diet are e ssential for good animal health and reproduction. Trace elements or microminerals are require d in smaller amounts and are equally as important as macrominerals. The trace elemen ts most likely to be deficient for grazing livestock are copper (Cu), cobalt (Co), selenium (Se), and zinc (Zn) in many parts of the world (McDowell, 2003). The Role of Macro-minerals in Beef Cattle Calcium Calcium is the most abundant mineral element in the animal body with approximately 99% in the skeleton and the rema ining 1% in the extra cellular fluids and soft tissues. Calcium, working in conjunc tion with phosphorus, makes up over 70% of the total mineral contents of the body, as 99% of Ca and 80% of body P constitute the bones and teeth (McDowell, 2003). Most of the Ca a nd P found in the bones exist in the form of either hydroxyapatite [Ca10 (PO4)6(OH) 2] or calcium phosphate [Ca3 (PO4)2]. Bones serve as metabolic pools for both these minerals, which may be drawn upon by the soft tissues of the body as and when needed. Thus, in times of metabolic demand in the body and also temporary shortfalls in the diet, th ese minerals may be mobilized from the bone metabolic pool to meet the needs not satisfied by dietary intake. Thus, during periods of emergency needs, the bodyÂ’s regulatory mech anism allowing minerals deposited in the bone to be drawn is an efficient one (Cunha, 1990). Calcium is involved in a number of biologi cal roles in the body, such as, for normal bone and teeth formation and maintenance, normal blood clotting, muscular contraction, regulation of the heart beat , secretion of certain horm ones, and milk production. Extraskeletal Ca occurring in the form of fr ee ions is essential for such physiological functions as nerve conduction, muscle cont raction and relaxati on, including that of

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6 cardiac muscles, and membrane permeability (M cDowell, 2003). In the synaptic nerve transmission processes, acetylc holine may not be liberated in the total absence of Ca ions (Scott et al., 1982). Calcium havi ng a role as a cofactor in many enzymatic reactions can stabilize and activate a numb er of enzymes such as -amylase, adenosine triphosphatase, lecithinase and ribonuclease (P eo, 1976). Calcium in adequate amounts in the diet reduces the risk for lead (Pb) poisoni ng, by decreasing Pb absorption in the gastrointestinal tract (Ballew and Bowman, 2001). Calcium is necessarily important for secretion of a number of hormones and horm one-releasing factors (A rnaud and Sanchez, 1996). Calcium also contributes to regulation of the cell cycl e by activating or stabilizing some enzymes (Hurwitz, 1996). Calcium is required for normal blood clotting. In this process, Ca ions apparently form a comp lex with prothrombin, which is acted upon by thromboplastin to form thrombin; thrombin th en acts on soluble fibrinogen to form the blood clot, fibrin. Intracellula r changes in Ca concentra tions modulated by vitamin D2 and calbindin, calmodulin and osteopontin, may be an important step in cell signaling (Carafoli, 1991), including the triggering of immune responses (N onnecke et al., 1993). Phosphorus Phosphorus has been called as the “master mineral” because of its involvement in most of the metabolic processes and functi ons in the animal’s body, more so than any other mineral element (McDonald et al., 1981; Harrison, 1984; Me lvin, 1984; Shupe et al., 1988). Phosphorus is the second most abundant mineral found in the animal body, next to Ca with approximately 80 to 85% in the inorganic portion of bone as Ca bound in the form of calcium phosphate and hydr oxyapatite (Underwood, 1981; Harrison, 1984;). Nonskeletal P, being the remaining 15 to 20%, is concentrated in the cells, the red blood cells, the muscle, nerve tissues and extrace llular fluids in organic forms as phosphoric

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7 acid esters, phosphoproteins, phospholipids, and nucleic acids. Extraskeletal P is a key component in the hormonal secondary me ssengers such as cyclic adenosine monophosphate ( cAMP ), cy clic guanine monophosphate ( cGMP ) and inositol polyphosphates. Nonskeletal P is a key element in high-en ergy phosphate bonds such as adenosine triphosphate (ATP), adenosine diphosphate (ADP) and creatine monophosphate (CMP), and plays a major role in providing the bodyÂ’s storage depots of readily available energy, thereby driving most metabolic reactions. Phosphorus plays a key role in the formation and mechanism of the nucleic acids, ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). These molecules make up chromosomes and control genetic inheritance (Lehninger, 1982). The nucleic acids are essen tial in cell growth and differentiation. The phosphorylation and dephosphorylation reac tions catalyzed by phosphorylases and phosphatases, respectively, drive and regulat e many activities intracellularly, including oxidation of carbohydrate, glycolysis , lipid tr ansport, inte stinal absorp tion and renal excretion (Georgievskii et al ., 1981). The rate of phosphoryl ation in the transcription process during protein synthesi s affects the rate of both tr anscription and translation, which, in turn, eventually affects the rate of protein production (Berner, 1997). Phospholipids are potential intermediates in the utilization of fat, which participate in the oxidation-reduction reactions i nvolved in the release of energy. Phospholipids also contribute to cell membrane fluidity and inte grity. Phosphorus occurring in the phosphate form (Lassiter and Edwards, 1982) helps to ma intain osmotic and acid-base balance, the buffer systems in the blood and body fluids, in cluding the ruminal fl uid, and the activity of the sodium/potassium (Na+/K+) pump in the body system. An important P containing

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8 compound, 2, 3-diphosphoglycerate regulates release of oxygen from hemoglobin (Arnaud and Sanchez, 1996; Berner, 1997; Underwood and Suttle, 1999). Phosphorus is also essential for proper f unctioning of the microorganisms in the ruminal fluids, especially those that are capab le of digesting cellulose mate rial from plants (McDowell, 1985). Ternouth and Sevilla (1990) reported that P is further involved in the control of appetite, and in the efficiency of feed util ization. Disturbances of glycolytic metabolism have been noted in the erythrocytes from cattle fed P deficient diets. Thus, P is arguably the most potent of all the minera l elements for animal production Potassium Potassium is ubiquitous in the body of mammals because it is required in large amounts by most organ systems for normal functioning. Potassium is the mineral constituent within the cell most involved w ith the regulation of osmotic pressure and acid-base balance. All soft tissues are much richer in K than in Na, making K the third most abundant mineral element in the animal body, surpassed only by Ca and P. There is a greater turnover for K in the body systems th an any other ions (Perry, 1994). Potassium constitutes over one half of the positively ch arged ions (cations) in saliva. Potassium is used in enzyme reactions involving phosphoryl ation of creatine and facilitates the uptake of neutral amino acids by the cells. The Na pump responsible for active transport mechanisms regulating the concentration of specific electrolytes handles the intracellular-extracellular separation of Na and K (Wilde, 1962). About 50% of osmolality of intracellular fluid is contributed by K, whereas Na and Cl together contribute 80% of the extracellular osmolality (Guyton, 1976). Potassium is the major determinant of resting membrane pot ential essential for cell transduction processes (Pet erson, 1997). The electrochemical gradients for K and Na

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9 participate in a number of processes in the body, such as nerve conduction, synaptic transmission, muscle contraction, fluid transport, hormone release and embryonic development (Underwood and Suttle, 1999). Potassium, as a principal base in tissues and blood, inevitably contributes to the regulation of acid-base balance and participates in respiration via the chloride shift. Potassium is responsible for maintaining the extracellular pH rigorously at 7.40 ± 0.05 (McDowell, 2003). Potassium plays an importa nt role in the tran sport of oxygen and carbon dioxide through the blood an d is required for at leas t half the carbon dioxide carrying capacity of the blood. Th e irritability of the nervous system and the eventual contractility of the muscle are dependant upon an ionic balance ex isting between Ca, K, Na, and Mg ions. The capillary and cell functi on, and excitability of the nerve and muscle are affected by these ions (Thompson, 1978). Potassium functions as an enzyme activat or and a cofactor in several enzymatic reactions including energy tr ansfer and utiliza tion, protein synthesis and carbohydrate metabolism. Potassium influences the enzymes participating in vital systems, of which the important ones are adenosine trip hosphatase, hexokinase, carbonic anhydrase, salivary amylase, pyruvic kinase and fruc tokinase. Many enzymes have specific or facilitative requirements for K ions, and the element influences many intracellular reactions involving phosphate wi th effects on enzyme activities and muscle contraction (Ussing, 1960; Thompson, 1972). Peterson (1997 ) reported a linear relationship existing between intracellular K concentr ation and cell growth and incorporation of amino acids into protein.

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10 Sodium and Chlorine Sodium and chlorine are commonly expresse d as a salt requirement and recognized as necessary constituents of the diet for graz ing cattle. Both these elements, along with K, in proper concentration and balance, are vitally indi spensable for a number of physiological functions. Sodium, as the chief ca tion of the extracellular fluids, is also an important ion in maintaining the body fluid balance, osmotic pressure and hydration of the tissues. Heart action and nerve impulse conduction and transmission are highly dependant upon proper proportions of Na and K. Another obvious function of Na is in the regulation of acid-base equilibrium within the body. These elements are consumed mainly as NaCl and excreted in the sa me form (Georgievskii et al., 1981). Sodium is a major ingredient of salts in saliva to buffer acid from the ruminal fermentation (NRC, 2001). When Na ion intakes increase, water intakes also increase to protect the intestine, facilitat e excretion and to clothe the enlarged osmotic skeleton with an appropriate volume of water (Wilson, 1966; Suttle and Field, 1967). The osmotic skeleton is sustained by the Na-K ATPase pum p in cell membranes. This pump actively transports Na out of the cell, thus convert ing the energy of ATP into osmotic gradients along which water can flow and fueling other cation-transporting mechanisms. The transmembrane potential differences established through th e activity of the pumps influence the uptake of other cations and are essential for excitability. The uptake of amino acids and glucose is enhanced by the Na ions in the lumen of the small intestine (Grim, 1980). Sodium affects th e utilization of digested protein and energy when there is a lack of Na in the body (McDowell, 2003). Fros eth et al., (1982) repor ted that the dietary Na in low levels affects protein and basic amino acid metabolism by reducing the utilization of these organic constitutents. Exchange of Na with H ion influences pH

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11 regulation, while that with Ca ion influen ces vascular tone. Calcium absorption and possible mobilization, as related to parturie nt paresis, are aff ected by the dietary electrolytes (West, 1987). The Na ion plays a key role in the uptak e of sugars by renal tubular epithelium and of amino acids by tissues and cells, muscle, bone, adipose, erythrocytes, fibroblasts , etc. (Grim, 1980). Sodium is also required for the absorption of bile salts in the ileum as a part of the enterohepatic circulation. Absorption of the water soluble vitamins, thiamin, riboflavin and ascorbic acid in the gastrointestinal tract may be Na-coupled (McDowell, 2000). Nucleosides fr om nucleic acids degraded by ruminal microbes are efficiently absorbed by Na depe ndant transport across the intestinal brush border membrane (Theisinger et al., 2002). Chlorine, the major anion of extracellular fl uid, functions as a part of gastric juice, in accompaniment with the H ion in the production of hydrochloric acid in the abomasum. Chlorine is important in prot ein digestion. Chloride ions are found in considerable concentrations in bile, pancreatic juice and intestinal secretions (McDowell, 2003). Chloride ions are necessary for activat ion of intestinal amylase (Ammerman and Goodrich, 1983). Chloride is involved in the “c hloride shift” which ai ds in regulation of the acid-base balance of the blood. The Cl ion exerts its base eff ect in blood plasma, thereby maintaining the desired acid-base rela tionship in the respiratory system (Block, 1994). Magnesium Magnesium, ranking second to K in quant ity in the intracellular fluids and organelles, is largely (80%) protein-bound and predominantly with the microsomes (Ebel and Gunther, 1980). Approximately 65% of to tal body Mg is contained in the skeleton; one-third of Mg in bone is in combination wi th P and the remaining part in the form of

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12 Mg ions and magnesium hydroxide is deposited within the hyd rate shell of the apatite crystal surface (Rook and Storr y, 1962). The Mg in the skel eton is responsible for the integrity of bones and teeth (McDowell, 2003). Magnesium also exists in relatively low but life-sustaining concentrations in extracellu lar fluids, including th e cerebrospinal fluid, and in blood, where it is present in both plasma and erythrocytes. Magnesium functions as an activator and a cofactor in more than 300 enzymatic reactions in intermediary metabolic proce sses (Shils, 1996). Magnesi um facilitates the union of substrate and enzyme by first binding to one or the other in the metabolism of carbohydrates, lipids, nucleic aci ds and proteins (Ebel and Gunther, 1980). Magnesium is vitally essential for oxidative phosphorylation, leading to ATP formation, which sustains processes such as the Na/K pump, py ruvate oxidation and conversion of -oxoglutarate to succinyl coenzyme A, and the phosphatetransferring enzymesdiphosphopyridine nucleotide kinase, myokinase, creatine kina se, alkaline phosphatase, hexokinase and deoxyribonuclease. In the -oxidation of fatty acids, Mg is required together with ATP for the activation of the firs t step involving acyl CoA s ynthetase (Shils, 1997). The transketolase reaction in the pentose monophosphate shunt is also Mg-dependant (Pike and Brown, 1975). Magnesium is predominantly associated with the mitochondria of the cells. Reis et al. (2000) reporte d that Mg is needed for normal insulin sensitivity and may be involved in early molecu lar steps of insulin action in the liver. Magnesium is complexed with the high energy molecules, ATP, ADP and adenosine monophosphate (AMP), in the tissues during ce llular respiration. Magnesium is needed at various steps in the synthesis of DNA, RNA and protein (B rody, 1999). Magnesium is also involved in the maintenance of electrical potentials ac ross nerve and muscle membranes, and for

PAGE 24

13 nerve impulse transmission, acti ng synergistically with Ca at some points and as an antagonist at other points throughout the neuromuscular j unctions (Ebel and Gunther, 1980; Shils, 1997). Magnesium also affects cell membrane integrity by binding to phospholipids. Sulfur Sulfur is an essential nutrient for all anim als as it is required for the formation of the many S-containing compounds found in esse ntially all body cells. Plants and the assimilatory gastrointestinal microflora of ruminants can synthesize S-amino acids and hence proteins from degradable inorgani c S sources (Underwood and Suttle, 1999). The S containing amino acid, methionine is a ke y amino acid since all other S compounds, except the B-vitamins thiamin and bio tin, which are essential for normal body functioning, can be synthesized from meth ionine. Sulfur containing compounds are involved in many vital metabolic functions of al l living cells such as acid-base balance of intraand extracellu lar fluids, protein synthesis, lipid and carbohydrate metabolism, blood clotting, enzyme synthesis, endocrine function, collagen a nd connective tissue formation through disulfide bonds between and w ithin polypeptide chai ns (Baker, 1977). Sulfur, in the form of highly active and free sulphydryl (SH) gr oups or disulphide bonds, maintains the spatial conf iguration of elaborate pol ypeptide chains and provides the sites for H bonding, as well as sites for the attachment of pr osthetic groups of enzymes and the binding to substrates that are essential to the activity of enzymes. Sulfur plays a key role as an integral part in the synthesis of biologically important molecules, such as hemoglobin, cytochromes, coenzyme A, coenzyme M, lipoi c acid, glutathione, heparin, penicillin G, metallothionein and sulfate polysaccharides including chondroitin. Sulfur containing coenzyme M, a 2-mercapto ethane-sulfonic acid, is required for the

PAGE 25

14 formation of methane from methylcobalami n (Taylor and Wolfe, 1974). Metallothionein, which is cysteine-rich, plays a significant role in protec ting animals from excesses of copper, zinc and cadmium while other cysteine -rich molecules influence Se transport and protect tissues from Se toxicity (Undewood and Suttle, 1999). Glutathione facilitates the uptake of Cu by the liver and also particip ates in the maintenance of proper redox potentials in cells. Sulfur is relatively abundant in the kera tin-rich appendages such as hoof, horn, feathers, wool fibre and mohair (Underwood and Suttle, 1999). Sulfur is present as sulfate in the c hondroitin sulfate of connectiv e tissue and in the natural anticoagulant heparin. Hormones such as insulin and oxytocin c ontain S amino acids as their prominent structural components. Sulfur is also an essential part of the water-soluble vitamins, thiamin and biotin, which have many diverse functions in metabolic reactions of the body (McDowell, 2000). The Role of Microminerals in Beef Cattle The trace mineral elements are the nutriti onally important minerals needed to make a successful beef cattle nutrition program, one that is productive yet economical. Although trace minerals are required in smalle r amounts than the macr ominerals, they are no less important to the physiological well bei ng of the animal. Indee d, the trace minerals have very well defined nutritional and bioc hemical roles that are considered to be essential. But these minerals can adversely affect animals that consume deficient or excessive concentrations. In other words, the deficiency or excess of these minor elements may be limiting production to a much greater extent than one might expect. In some grazing situations, some of these minerals may be marginally or severely deficient.

PAGE 26

15 Even marginal deficiencies in the animal diets may be of economic importance to beef producers through reduced growth, reproduction and (or) health status (Spears, 1988). Beef cattlemen should become acquainted w ith the cattleÂ’s requirements of these minor minerals, the amount of these require ments that can be provided from the forage produced on their pastures and (or) the amount of minerals that can be delivered in a well-balanced animal diet. It has now become evident that many health problems and failures of commonly accepted disease treatments have had trace mineral deficiencies as the root cause or a contributing factor. Alt hough others may be involved, much work with copper (Cu), zinc (Zn), and selenium (Se) ha s shown these minerals to be essential for maintaining good immune systems and disease defense mechanisms in cattle. Copper Copper is a key component of several meta lloenzymes, surpassed only by Zn in the number of enzymes activated, which when impa ired can directly or indirectly cause many of the clinical signs of Cu deficiency (Underwood and Suttl e, 1999). The essentiality of Cu for bone development, normal Fe metabo lism, cellular respiration, proper cardiac function, elastin and collagen synthesis, melanin production, integrity of the central nervous system and reproduction are all well recognized (Suttle, 1987). Copper deficiency that is a serious problem for grazing ruminants in many countries of the world is due both to low concentrations of the elem ent in forage as well as to elevated amounts of molybdenum (Mo) and (or) S, which interf ere with Cu utilization (McDowell, 2003). This deficiency has detrimental effects on numerous organs and tissues, including the hematopoietic system, cardiovascular sy stem, central nervous system and the integumentum (Miller et al., 1979)

PAGE 27

16 Copper containing enzymes are widely di stributed within the body. They perform several diverse functions incl uding catalysis of oxidation/ reduction reactions and the protection of the cellular level against superoxi de radicals. At least fourteen enzymes are known to be dependant upon Cu for their f unctions (Linder, 1996). Cuproenzymes of biological importance include cytochrome oxi dase, lysyl oxidase, Cu-Zn superoxide dismutase, dopamine-hydroxylase, tyrosinase, factor IV and thiol oxidase (OÂ’Dell, 1990). Copper functions both as an antioxidant in vivo and as a pro-oxidant in vitro, and accumulation of tissue Cu may lead to oxidati ve stress (OÂ’Conner et al., 2000; Rock et al., 2000). The enzyme cytochrome oxidase plays an active part in the cellular respiration as the terminal oxidase that catalyses the reduction of O2 to water (McDowell, 2003). Superoxide dismutase, which is now being gi ven an increasing amount of attention, is required to prevent the accumulation of the superoxide radicals, a cause for cellular damage (Taylor et al, 1988). Dopamine-hydroxylase is essentia l in the conversion of dopamine to noradrenaline, a neural hormone that plays a vital part in the transmission of nerve impulses (OÂ’Dell, 1990). Lysyl oxidase is needed for the proper cross-linking of elastin and collagen during th e building, maintenance and re pair of connective tissue including that needed for wound healing and maintaining the integrity of blood vessels (Linder, 1996; Rucker et al., 2000). Copper plays a significant role in hem oglobin formation, Fe absorption from the small intestine and Fe mobilization from the tissue stores. Ceruloplasmin, a Cu containing 2-globulin which is synthesized by the liv er, is necessary for the oxidation of Fe, permitting it to bind with the Fe tran sport protein, transferrin (Evans, 1978). Ceruloplasmin aids in the flow of Fe that supports hematopoiesis in conjunction with

PAGE 28

17 ferroxide II, another Cu-dependant enzyme (Linder, 1996; Gabrielli et al., 2000). The transfer of Fe from mother to fetus across the placenta and its upt ake through transferrinreceptor mediated endocytosis are mediated by serum ceruloplasmin (Danzeisen et al., 2000). The Cu metalloenzyme, tyrosinase, aids tyrosine in the formation of the melanin polymer that protects skin against excess ultraviolet light, and determines the pigmentation of hair. Copper is required for formation and incorpor ation of disulfide groups in keratin synthesis. In mammals fe d Cu deficient diets, reproductive failure commonly occurs (Underwood, 1977). Copper deficiency signs of physiological significance include anemia, diarrhea, bone disorders, neonatal ataxia, changes in hair and wool pigmentation, infertility, cardiovascular disorders, im paired glucose and lipid metabolism, and a depressed immune system (Davis and Mertz, 1987). On e of the most dramatic signs of this deficiency is the massive internal hemo rrhage, which result from angiorrhexis or spontaneous rupture of a major vessel such as the aorta. In cat tle with hypocupremia associated with Mo, the antibody response to Brucella abortus antig en has been lowered (Cerone et al., 1995). The subsequent leucocyt e count is a more convincing evidence of Cu deficiency in a study with heifers (Art hington et al., 1996; Ge ngelbach et al., 1997). Copper deficiency also reduces macrophagic ability, an index of phagocytotic activity (Harris, 1997). Iron Iron is by far the most abundant trace elem ent in the body and its value as a dietary constituent has long been recognized and appreciated because of the multitude of biological functions. Approximately 60% of total body Fe is present as hemoglobin, a complex of the protoporphyrin, heme and globin. Practically all of the Fe in the animalÂ’s

PAGE 29

18 body is organic in nature and only a very small percentage is found as free inorganic ions (Georgievskii, 1982). Iron, be ing a key mineral in many biochemical reactions, is involved in several enzyme systems responsible for O2 transport, and for activation of oxygen and for electron transfer. Iron content of the body varies with species, age, sex, nutrition, and state of health, a nd is controlled by adjustment in absorption rate (Finch and Cook, 1984). The presence of Fe in the animal body is in many complex forms, as protein-bound compounds (hemoproteins), as heme compounds (hemoglobin or myoglobin), as heme enzymes (catalase, peroxidase, mitochondria l and microsomal cytochromes), and as nonheme compounds (flavin-Fe enzymes, transf errin, and ferritin). Myoglobin represents about 4% of total Fe (Brody, 1999). Hemoglobin is packaged in erythrocytes and allows the tissues to breathe and accounts for over 90% of the total prot ein of these cells (Davies, 1961). Myoglobin is the less abundant Fe-porphyrin found in muscle, where its affinity for oxygen completes the transfer of oxygen from oxyhemoglobin into the sites of oxidation in muscle cells (Fruton and Si mmonds, 1958). The ability of Fe to change between the divalent (Fe²+) and trivalent (Fe³+) state allows the cytochromes a,b and c, Fe containing enzymes, to participate in the el ectron transfer chain. Ir on containing catalase and peroxidase remove potentially danger ous products of metabolism, the peroxide molecules, and Fe activated hydroxylases in fluence connective tissu e development. Iron is involved at every stage of the tricarboxylic acid (Krebs) cycle, as all of the 24 enzymes in this metabolic pathway consist of this element either at their active sites or as essential cofactors (McDowell, 2003).

PAGE 30

19 Cytochrome C, an important Fe enzyme lo cated in the electron transfer chain in mitochondria is necessary for cellular producti on of energy. Cytochrome C is in high concentration in the tissues that facilitates a high rate of O2 utilization, such as the heart muscles (Dallman, 1990). Cytochrome P-450, a family of enzymes located in the microsomal membranes of hepatic cells, is invo lved in the oxidative degradation of drugs and other endogenous substrates. Other importa nt enzymes, ribonucle otide reductase, are required for DNA synthesis, and phosphoenol pyruvate carboxylase is a rate-limiting enzyme in gluconeogenesis. A Fe containi ng glycoprotein, lactofer rin, is secreted by mammary cells and has an antibiotic activity in the mammary gland (Troost et al., 2002). Lactoferrin when fed to calves increased consumption of calf starter and improved performance (Joslin et al., 2002). Iron defici ency in grazing animals is generally the result of blood loss from hea vy parasite infestation rather than nutritional inadequacy. Signs of Fe deficiency include anemia, lowe r weight gains, listlessness, inability to withstand circulatory strain, labored breathing after mild ex ercise, reduced appetite and decreased resistance to infection. Iron de ficiency leads to decreased hemoglobin concentration in the cardio-vascular system , which eventually affects many functions through the reduction in tissue oxygenation. Zinc Zinc (Zn) has long been considered to be essential for plants, animals and humans (Hambidge et al., 1986), and is recognized to be associated with over one thousand known proteins in the body system (Maret, 2002). This element appears to participate in metabolism in at least two ways, as an e ssential component of certain enzymes and through its influence on the structural confi guration of certain none nzyme organic ligands (Parisi and Vallee, 1969). Zinc activates several enzymes and is an integral constituent of

PAGE 31

20 various important metalloenzymes includi ng carbonic anhydrase, carboxypeptidase A and related peptidases, alkaline phosphatase , alcohol dehydrogenase, lactate, malate, glutamate dehydrogenases and cytosolic superoxi de dismutase. Zinc, as a component of RNA and DNA polymerases, is actively invo lved in protein bi osynthesis. Carbonic anhydrase, which contains about 0.3% Zn, is present in erythrocyt es and catalyzes the synthesis and break down of carbonic acid, and plays a vital role in maintaining the desired acid-base equilibrium of the body. Zinc is critically involved in many biol ogical mechanisms including those related to cell replication, differentiation and also in the development of cartilage and bone (Hambidge et al., 1986). Zinc is largely involved in all major metabolic processes of the bodynucleic acid metabolism, protein synt hesis and carbohydrate metabolism. This element influences and enhances cellular divi sion, growth and repair in rapidly growing tissues by facilitating the synthe sis of RNA, DNA and protein. In its deficiency, the DNA damage is induced and the cellÂ’s ability to re pair this damage is eventually compromised (Ho and Ames, 2002). Another impo rtant biological f unction of Zn is the initiation of apoptosis or programmed cell death, which de stroys cancerous and pre-cancerous cells. Because of the involvement in the transcrip tion and translation of genetic material, Zn proteins are accounted for their essentiality to all forms of life (Vallee, 1988). The Zn metalloenzymes, retinal reductase and al cohol dehydrogenase, are necessary for the interconversion of vitamin A alcohol (retinal) to vitamin A aldehyde (retinal), a process essential for normal vision (McDowell, 2000) . Zinc is necessary for maintaining the normal concentrations of vitamin A in plasma and facilitating the normal mobilization of vitamin A from the liver (Smith et al ., 1973; Kelleher and Lonnerdal, 2001).

PAGE 32

21 Zinc is associated with pa ncreatic concentrations of insulin and the dietary Zn deficiency reduces markedly this hormone c oncentration in both pancreas and plasma. The impairment in corticosteroid synthesi s by adrenocorticotropic hormone (ACTH) with inadequate Zn levels is sugge stive of ACTH being functiona lly dependant on this mineral element (Flynn et al., 1972). Zinc plays an im portant role in speci fic immune defenses such as humoral and cell-mediated immunity (F raker et al., 2000). Zinc also influences nonspecific immunity by its effect on neutroph ils and natural killer cell activity (Shankar and Prasad, 1998). Zinc is required for th e activation of thymu lin, a hormone that stimulates the development of white blood cells into T-lymphocytes with specific functions (e.g., “helper,” “suppressor,” and “killer” T cells); (Yoshida et al., 1999). Gonadal maturation, spermatogenesis and the development of the primary and secondary sex organs in males and all stages of the re productive process in females from estrus to parturition and lactation can be adversely affected by Zn deficiency. In Zn deficient animals, bone collagen synthesis and tur nover are markedly reduced, with reduced activity of tibial collagenase, a zinc metalloenzyme (Starcher et al., 1980). Manganese Knowledge concerning the metabolism a nd function of manganese (Mn), which was first found to be an essential minera l element for growth and reproduction in experimental animals in 1931, has increased c onsiderably during the past years. As a component of various enzymes, Mn fulfils specific biochemical functions in the body. Pyruvate carboxylase, arginase and Mn-supero xide dismutase are the most important Mncontaining enzymes recognized along with a limited number of metalloenzymes (Hurley and Keen, 1987). The enzymes activated by Mn in clude a number of hydrolases, kinases, decarboxylases and transferases (Groppel and Anke, 1971). This element is an integral

PAGE 33

22 part of enzyme compound that acts in the synthesis of chondroitin sulfate, which is a component of mucopolysaccharides present in the organic matrix of bone. Many glycosyl transferases, enzymes of importance in synt hesis of polysaccharid es and glycoproteins, require Mn for activity (Leach, 1971). Manganese contributes to proper functioning of the reproductive process in both males and females. Hidiroglou (1975) reported that Mn uptake is greater in the ovine Graafian follicle and corpus luteum when compared to other reproductive tissues, and suggested that Mn may be essential for normal ovarian function. Manganese is also involved in the formation of prothrombi n, a glycoprotein, through its activation of glycosyltransferases. The clot ting response from vitamin K is reduced in Mn-deficient chicks (Doisey, 1974). Pyruvate carboxylase is involved in sustaining lipid as well as glucose metabolism. The fat accumulation seen in Mn deficient animals is also a feature of biotin deficiency in non-ruminants as biotin activates the same enzyme (Underwood and Suttle, 1999). Manganese is necessary as a cofactor in the enzyme that catalyses the conversion of mevalonic acid to squalene, a nd stimulates synthesis of cholesterol and fatty acids. Manganese stimulates arginase activ ity and may play a regulatory role in urea production. Mitochondria are respon sible for 60% of cellular O2 consumption and may be particularly vulnerable to free radical da mage (Leach and Harris, 1997). Manganese superoxide dismutase (MnSOD) catalyses the dismutation of the free oxygen radical to hydrogen peroxide and O2, and thus functions as a de fense against the deleterious reactions of this free radical and protects the integrity of cell membranes. Manganese deficiency lowers MnSOD activity in the he art and increases the peroxidative damage caused by high dietary levels of polyunsat urated fatty acids (PUFA) (Malecki and

PAGE 34

23 Greger, 1996). Manganese is also involved in the biosynthesis of choline and both these are needed for prevention of perosis in poultry. Manganese is important to the functions of the immune system of the body (Hurley and Keen, 1987). The noticeable signs of Mn deficiency ar e skeletal abnormali ties in young animals and, in older animals, lower reproductive performance resulting from depressed or irregular estrus, low concepti on rate, abortion, stillbirths a nd low birth weights. Maas (1987) indicated that Mn deficiency has been associated with the anestrus condition in cattle. Abnormalities in cell function and ul trastructure, particularly involving the mitochondria occur in Mn deficiency (Hurley and Keen, 1987). Cobalt The first evidence that cobalt (Co) is a dietary essential nutrient was obtained as early as 1935 from Australian research into the cause of two naturally occurring debilitating diseases of sheep and cattle known locally as “coast disease”( Lines, 1935; Marston, 1935) and “wasting disease” (Underwood and Filmer, 1935). The only estabilished physiological function of Co is its role as an in tegral part of the vitamin B12 molecule. Under normal situations, domestic ruminants are not dependant on a dietary source of vitamin B12 because ruminal microorgani sms can synthesize vitamin B12 from dietary Co (NRC, 1996). Smith reported that the amount of dietary Co converted to vitamim B12 in the rumen ranged from 3-13% of intake. Vitamin B12 is an essential part of certain en zymes involved in metabolic reactions. Vitamin B12 contains about 4.5% Co, and is referred to as cobalamin. Most of the cobalamins occur in two coenzyme fo rms, adenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl) (NRC, 1996; McDowell, 2003). Cyanocobalamin (B12) is converted within the cells to either MeCbl, a coenzyme for methyltransferase, or AdoCbl,

PAGE 35

24 the coenzyme for mutase (McDowell, 2003). Methylcobalamin is important for microbes as well as mammals and is needed for methane, acetate and methionine synthesis by rumen bacteria (Poston and Stadman, 1975) . Adenosylcobalamin influences energy metabolism, facilitating the formation of gl ucose by assisting methylmalonyl coenzyme (CoA) mutase to form succinate from pr opionate, chiefly in the liver (Smith, 1987; McDowell, 2003). The enzyme, 5-met hyltetrahydrofolate homocysteine methyltransferase is also a vitamin B12 dependant enzyme that is heavily involved in one C and methionine metabolism. Vitamin B12 also influences lipid metabolism via its effect on the thiols (McDowell, 2000). Cobalt deficiency in ruminant s is actually a vitamin B12 deficiency. Early signs of Co deficiency are decreased appetite, reduced milk production, and either failure to grow or moderate weight loss, and with severe de ficiency, animals exhibit unthriftiness, rapid weight loss, fatty degeneration of liver and pale skin and mucous membranes as a result of anemia. The immune response in sheep has been shown to be affected by Co-vitamin B12 deficiency (Vellema et al., 1996). Molybdenum Evidence of biological function of molybde num (Mo) was reported in 1953 when it was discovered that the flavoprotein, xanthi ne oxidase is a Mo metalloenzyme, whose activity depends on the presence oh this el ement. Molybdenum is found in nearly all body cells and fluids, but its essentiality is due to its biochemical role in the enzymes xanthine oxidase, sulfite oxidase and al dehyde oxidase (Mills and Davis, 1987). Xanthine oxidase , which contains both Mo and Cu, is involved in the reduction of Fe (3+ ferritin to 2+ ferritin) in Fe meta bolism (De Renzo et al., 1953; Mahler et al., 1954; Seelig, 1972). Xanthine oxidase and aldehy de oxidase are involved in the electron

PAGE 36

25 transport chain in the cells together with cytochrome C (Rajagopalan, 1980). Aldehyde oxidase may also be involved in niacin me tabolism. Sulfite oxidase favors oxidation of sulfite to sulfate for final excretion in the urine. The metalloenzymes containing Mo are actively involved in the meta bolism of purines, pyrimidines, pteridines and aldehydes, and in the oxidation of sulfite (Brody, 1999). The metabolism of Mo is affected by Cu and S, which are antagonistic to this element. Molybdenum may enhance microbial ac tivity in the rumen in some instances. Sulfide and molybdate interact in the rumen to form thio molybdates, the compounds that cause decreased absorption and reduced post-absorption metabolism of Mo, and increased urinary excretion of Mo (Underwood and Suttle, 1999). Molybdenum deficiency is most often related to excess Cu and animals perform normally on extremely low levels of Mo in the diet (McDowell, 2003). Loss of appetite re flects the needs of microorganisms for Mo for cellula r digestion (Shariff et al., 1990). Selenium The dietary requirements of selenium (S e) and its metabolism are influenced by many nutrient interrelationships including its interactions with S, lipids, vitamin E, proteins, amino acids and several microminer als. Selenium is part of at least two metalloenzymes and its functions are interrela ted with vitamin E. Knowledge of Se and vitamin E in nutrition and metabolism has been reviewed extensively (NRC, 1980; Mertz, 1986). Selenium is required as a metallic coen zyme for glutathione peroxidase (GSH-Px), which acts as part of the ce llular antioxidant defense syst em (NRC, 2000). Vitamin E is also essential to this system that is nece ssary to prevent cellular destruction due to hydrogen peroxide and lipid hydr operoxides (Hoekstra, 1974). Thus, Se plays a central role in maintaining the integr ity of cellular membranes.

PAGE 37

26 Selenium is also a cofactor in enzymes involved in thyroid fu nction (Arthur et al., 1988). Iodothyronine 5`-deiodinase, a sec ond selenometalloenzyme, catalyses the deiodination of thyroxine (T4) to the more metabolically active triiodothyronine (T3) in tissues (Arthur and Beckett, 1994). Selenium performs its functions mainly through the selenoproteins, and there are approximately 30 to 35 selenoproteins detected in mammalian tissues (Behne et al., 2000; Kryukov et al., 2003). Selenoprotein P, the principal constituent of plasma Se, contribu tes to Se transportation, has a redox function and may protect cell membranes (Awadeh et al ., 1998; Burk et al., 2003). Selenium is also required for normal pancreatic morphol ogy, and through this effect on pancreatic lipase production is resp onsible for normal absorption of lipids and tocophenols from the gastrointestinal tract. Vitamin E, Se and S containing amino acids, through different biochemical mechanisms, are capable of preven ting some of the same nutritional diseases (McDowell, 2000). Both Se and vitamin E have the sparing effect on each other (Scott et al., 1982). Selenium also has a strong tendency to complex with heavy metals and exerts a protective effect against the heavy meta ls, including cadmium, mercury, and silver (McDowell et al., 1978; Wha nger, 1981; Underwood and Suttle, 1999). Selenium appears to be involved in the metabolism of sulphydral compounds (S prinker et al., 1971; Broderius et al., 1973). Selenium is necessary for growth and fertility in animals and for the prevention of a variety of disease conditions . Selenium may be particularly needed for male fertility (Marin-Guzman et al., 1997) and also particularly prot ective to the kidney (Liebovitz et al., 1990). Signs of a pronounced dietary Se deficiency include reduced growth and extensive degeneration of muscle tissue (w hite muscle disease) in young animals. Other signs of Se

PAGE 38

27 deficiency are stiffness, lameness and possi ble cardiac failure. In older animals the deficiency signs are unthriftiness, emacia tion, diarrhea, anemia, poor body weight and reduced reproductive performance (Godwin et al., 1970). Stabel and Spears (1993) reported that Se deficiency also adversely a ffects the immune response in the animals. Mineral Composition of Forages Forages represent a diverse range of feedst uffs that make a significant contribution to the overall economy of meat, wool a nd milk production. Beef cattle production throughout the world is based on forages, with pastureland forages being predominant. A major attractant to grazing animals is the re latively high palatability, quality and variety of forages in pastures. Grasses and other forages are generally highly effective at maximizing uptake and incorporation of availabl e forms of nutrients into their biomass. Within grassland based livestock production systems, the role of the animal has an overriding influence on nutrient fluxes. Fo rage mineral composition can have a significant effect on animal performance and hea lth, as they are often not in balance with the nutrient requirements of the animal s (Grunes and Welch, 1989; Mayland and Wilkinson, 1989) Grazing management is principally invol ved in managing and maintaining the grazing animal-forage plant-soil complex to obtain specified objectives. This is accomplished by blending ecological, economic and animal management practices. Grazing management systems designed for impr oved pastures can generally target the maximization of animal production in the short term. Such pastures are mostly limited to growing season utilization during the immature growth stages and are often compromised of forage species relatively tolerant of grazing. Sustainabl e pasture management depends upon adequacy and balance of supply of nutri ents to meet the requirements of an

PAGE 39

28 appropriate level of dry matte r production of sufficient nutr itional quality for livestock. The requirements, roles and functions of mine rals in pasture management for both plants and animals are well known and have b een reviewed extensively over the years (Whitehead, 2000; Tunney et al., 1997). Grazing animals derive a high proportion of their minera l nutrients from forages that they consume. Mineral requirements of the animals ar e dependant upon the age, sex and stage and level of producti on, and can even vary across breeds within a species of livestock. Forage content of various minera l elements varies considerably and is dependant upon the interaction of a numb er of factors including soil mineral concentrations, plant species, stage of maturity, pasture management and climate (McDowell, 1985). Forage mine ral concentrations are also influenced by fertilization, season of the year and the inte rrelationship with other elemen ts. Most naturally occurring mineral deficiencies in herbivores are associ ated with specific re gions of the world and are directly related to soil characterist ics of the region (McDowell, 1996). Adequate intake of forages by grazing ruminants is e ssential in meeting mineral requirements. Forage intake of grazing anim als varies with the body wei ght as well as with forage quality and availability. Forage dry matter consumption by most grazing ruminants is about 2% of their body weight per day when values for different seasons are averaged across the year. However, considerable seasonal variation occurs with values as low as 1% during periods when forage is low in quality and availability, to over 2.5% when quality and availability are high. Forage mineral analyses are preferable to soil analyses, while appropriate animal tissue and fluid analyses most accurately po rtray the contribution of the total dietary

PAGE 40

29 environment (forage, soil, water, etc.) in meeting livestock mineral requirements McDowell et al., 1986). Forage mineral com position is dependant on many factors, including soil characteristics (Brady, 1984), stage of plant gr owth (Greene et al., 1987), climatic conditions and fertilization practices (Mayland et al., 1990). Forage Macrominerals Calcium and Phosphorus Calcium is an important mineral element for beef cattle, both in terms of the relative requirement and the di versity of functions in the animalÂ’s body. Calcium is a major component of the skeleton, which also serves as a Ca storage site. Forages are generally good sources of Ca for grazing livesto ck, while cereal grains are poor sources. Legume forages contain high levels of Ca, wh ile grasses contain only moderate amounts. Calcium is available in adequate amounts in high quality forages, although Ca can be deficient in weathered or mature forage. The Ca content of forage is affected by plant species, portion of plant consumed, maturity, quantity of exchangeable calcium in the soil and climate (McDowell, 2003). Temperate forage s generally contain more Ca than those grown in the tropics. Minson (1990) publis hed average values as 1.42 and 1.01 % Ca (DM) for temperate and tropical legume s, and 0.37 and 0.38 % Ca (DM) for the corresponding grasses. Concentrations of Ca and P in crops and forages are dependent on soil factors, plant species, stage of maturity, crop management, climate, and soil pH (McDowell, 1985). As the age of plant increases the mineral cont ents of grasses decrease while forage Ca concentration is less affected by advancing maturity (Gomide, 1978), thereby resulting in a detrimental widening of the ratio of Ca with P. The leaf of the forage plant contains twice as much calcium as the stem, and pastur e forage Ca concentrations are increased by

PAGE 41

30 applying nitrogenous fertilizer. Slowing of pasture growth by flooding and a seasonal decline in soil temperature increase forage Ca levels (Underwood and Suttle, 1999). The most frequently observed cases of Ca defi ciency occur in cattle fed high amounts of concentrate feed and in cattle grazing ma tured small grain forages (McDowell, 2003). The preference and ability of grazing an imals to select forages of higher P concentration has long been recognized (Jones and Betteri dge, 1994). Phosphorus plays a pivotal role in energy metabolism, with decreas ed energy utilization t ypical in P-deficient animals (Greene et al., 1985). Thus, a P defici ency can cause immediate repercussions in terms of performance. Phosphorus deficiency has been described as the most prevalent mineral deficiency throughout the wo rld for grazing livestock (Underwood, 1981; McDowell, 1985). The P status of forages vari es widely and is influenced primarily by the P status of the soil, the stage of maturity of the pl ant and climate. Grains are considered a good source and forages are defici ent suppliers of P. Therefore, pasture and forage based diets are defici ent in P (McDowell, 2003). Mi nson, (1990) and Jumba et al., (1995) suggested that on average, P concentrations increase by 0.03-0.05g kg-1 DM mg-1 extractable soil P. Temperate forages generally contain more P than tropical forages (0.35 vs. 0.23 % DM) and legumes slightly more than grasses (0.32 vs. 0.27 % DM) (Minson, 1990). Young growing grass pastures are of ten adequate in P (>0.3%) during early growth but then decline rapidly in P at in creased stages of matu rity (McDowell, 1997). Distribution of P along the pl ant structure is relatively uniform, and forage P concentrations and digestibility declines with advanced maturity and weathering. The cool season forages are high in P and low in Ca during immature stages of growth (Underwood and Suttle, 1999). Phosphorus deficien cy can result in reduced feed intake,

PAGE 42

31 poor feed efficiency, decreased growth rate , skeletal abnormalities and reproductive failure. Magnesium Magnesium is closely related to Ca and P in its dispersion and functions in the animal body. Magnesium concentration in forages varies greatly depending on plant species, soil Mg, stage of growth, season a nd environmental temperature (Minson, 1990). Forages generally contain adequate levels of Mg during most of the year, but levels can be very low during times of rapid growth in the spring and fall, especially in wellfertilized pastures. The Mg content in forage s is about twice the level of the element in cereals which contain 0.11 to 0.17 % Mg (Underwood, 1981). Leguminous plants are usually richer than grasses in Mg, as they are in Ca (Thomas et al., 1952; Turner et al., 1978). Minson (1990) reported that the concen trations were 0.18 and 0.36 % Mg (DM) respectively, for temperate and tropical grasses, and 0.26 and 0.28 % Mg (DM) for the corresponding legumes. The Mg content in cer eal grains is generally 0.11 to 0.13 % DM and is less variable among species. The Mg requirements for growing, pre gnant, and lactating beef cattle are 0.10, 0.12, and 0.20% of the diet DM respectively (NRC, 1996). The change in requirement from gestation to lactation occurs very rapi dly and can result in the metabolic disorder, grass tetany, in cows grazing cool season fora ges such as oats and wheat (Mayland et al., 1990). The reduction in standing stockpiled fora ge Mg concentration can be substantial during the winter months. Potassium, which is high in lush-growth cool season forage species, has been shown to reduce Mg absorpti on in the ruminant stomach (Fontenot et al., 1989; Greene, 2000). The low level of Mg in forage often corresponds to calving seasons and the onset of lactation, which is when cow requirements are highest. Grass

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32 tetany is not as prominent in cows grazing warm season perennial pastures, even though dietary Mg levels may be below the requireme nt (0.20%). The apparent depression in Mg contents results from the high water content of rapidly growing plan ts. High fertilization with K and/or N, especially in soils with low Mg content, reduces the Mg content in grasses (McDowell, 2003). Magnesium require ments may be increased by feeding high levels of Al, K, P, or Ca as these minera ls decrease the efficiency of Mg absorption and/or utilization (Wise et al., 1963; Newton et al., 1972; Greene et al., 1983) . Magnesium deficiency in beef cattle resu lts in nervousness, reduced feed intake, muscular twitching and staggering gait, and in advanced stages, convulsions occur, the animal cannot stand and eventually deat h soon follows (Church and Pond, 1975; NRC, 1996). Potassium Forage supply of proper amounts of K, th e third most abundant mineral in beef cattle, is important. Forages are excellent sour ces of K, usually containing 1 to 4% (DM). When forage is growing and immature, K con centration is high and generally exceeds the requirements of all classes of cattle. Thus K is seldom a limiting mineral for pasture animals. However, K is soluble in plant ti ssues and is rapidly depleted in standing stockpiled forage that has been rained on. Th e K contents of forage are affected by a number of interrelated factors such as plant maturity, species as well as variety within a species, management procedures such as graz ing or crop removal system, fertilization, particularly with K and nitrogen, soil and environmental conditions (McDowell and Valle, 2000). Robinson (1985) reported that c ool season grass species maintain higher K concentration than warm season species. Trop ical legumes have lower levels of K than

PAGE 44

33 temperate legumes (Lanyon and Smith, 1985) . Potassium concentration decreases markedly as the season progresses fo r a given sward (Reid et al., 1984). Forage K concentration changes duri ng growth for physiological reasons independent of soil K level (Grimme, 1976). Forage maturity also lead s to a reduction in K contents and low concentrations are obs erved in weathered range forage (Clanton, 1980). The concentration of K required for b eef cows during lactation is 0.70 % DM (NRC, 1996). Cattle consuming diets with mo re than 3% K while grazing lush pastures experience reduced Mg absorption and the rela ted Mg deficiency symptoms (Church and Pond, 1975, NRC, 1996). High level of K has the effect of exacerbating the already low Mg content of the lush forage and increasing the risk of grass tetany. Sodium and Chlorine Both Na and Cl are electrolytes that regulate cellular osmotic pressure, Na+/K+ pump activity, and acid-base balance (Underw ood and Suttle, 1999). Forage Na is often below animal requirements and grazing cattle require supplemental salt. However, cattle crave salt and may consume it in excess when it is provided free choice (Greene, 2000). The Na content of forages varies consid erably (Minson, 1990). Many of the pasture forages contain only 0.03% DM Na (McDowe ll, 2003). When it is not supplemented to the beef cattle, Na can be the limiting nutrient in the diet. Cattle grazing pastures consume more salt during spring and early summe r when more succulent than later in the season when the forage is drier (Underwood and Suttle, 1999). Tropical pasture species generally accumulate less Na than the te mperate species (Morri s, 1980) and thus, Na deficiency is more likely to occur in livesto ck of tropical regions. Cereal grains and vegetable protein concentrates are fairly low in Na, containing 0.01 to 0.06%. Sodium

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34 requirements in non-lactating beef cattle do not exceed 0.06 to 0.08% DM while lactating beef cows require approximately 0.10% DM Na (Morris, 1980; NRC, 1996). Forages invariably provide sufficient Cl fo r grazing beef cattle. Most pastures are appreciably richer in Cl than they are in Na with little difference between legumes and grasses or between fresh grass and hay. Cereal grains generally provide more Cl than Na, and cereal straws contain 3to 6fold more Cl than the grains (Underwood and Suttle, 1999). The concentration of Cl required for beef cows is not well defined, but the amounts provided by dietary salt supplementatio n appear to be ad equate (Church and Pond, 1975; NRC, 1996). In most circumstances, Na and Cl concentrations decline as grasses mature but less so in legumes (U nderwood and Suttle, 1999). Reid and Horvath (1980) reported that the use of potassium chlo ride (KCl) as a K fertilizer increased plant Cl but depressed Na concentrations in fora ge due to the antagonistic effect of K. Sulfur Beef cattle need sulfur (S) for rumen bacterial growth and protein synthesis. The S concentrations found in pasture and conserve d forages range very widely, from 0.05 to > 0.5 % DM, depending mainly on the availability of soil S, N, and P, and the maturity of the sward (McDowell, 1985; Underwood and Suttl e, 1999). The type of forages provided for grazing beef cattle may infl uence S requirement and bioavailabilty. Plant species vary in their S requirement. The S conten t in pasture forages averages 0.32 % DM. Grasses are higher in S concentrations than legume forages. The availability of S to animals is greater when it is obtained fr om forages than from a dietary mineral supplement.. In relation to animal requirement s, temperate forages are generally adequate in S compared with tropical plants. Cereal grai ns are quite low in S with corn, rice, rye, sorghum, and wheat ranging from 0.05 to 0.18 % (McDowell, 2003).

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35 The concentration of S required for beef cattle is 0.15 % DM (NRC, 2000). Forages grown on soils very deficient in S have ve ry low concentration of S far below those needed by animals (Rendig, 1986). The major pr oblem with consuming S at levels higher than requirements is the antagonistic effect of S on Cu availabili ty. Forages with high S content of more than 0.40 % DM will ge nerally bring about copper deficiency. The maximum tolerable concentra tion of dietary S has been estimated at 0.40 % DM (NRC, 1980), and the excess of S can be a practical pr oblem in some situations.. Deficiency of S, a component of some amino acids and some vitamins, causes reduced feed intake and decreased microbial digestion and protei n synthesis (Underwood and Suttle, 1999). Forage Microminerals Copper Copper contents of pastures and forages vary with the species, cultivar, and maturity of plants, the soil conditions and fertilizers used (McFarlane et al., 1990). Forage Cu is less influenced by soil pH. The concentrations of Cu are lower in temperate grasses (4-7 ppm DM) than legumes (7-8 ppm DM), and under tropical conditions, legumes are lower in Cu (3-6 ppm DM) than the grasses (7-8 ppm DM) (Minson, 1990). Copper is unevenly distributed in temperate grasses with the leaves containing 35 % (on average) higher concentrations than stems. The values in the whol e plant decline during growing season (Minson, 1990). Grasses, averaging 5 ppm, tend to be lower in Cu than are legumes which average 15 ppm. Cereal grains contain 4 to 8 ppm Cu and the leguminous seeds generally contain 15 to 30 ppm (Davis and Mertz, 1987). The Cu availability in cereal grains may be ten times greater than in forages (Suttle, 1986). Jumba et al (1995) reported from Kenya that significant speci es differences in forage Cu concentrations exist between Kikuya grass (hig h in Cu) and Rhodes grass (low in Cu).

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36 Cu requirements are suggested to be 10 ppm DM intake but can vary depending upon other dietary components (NRC, 2000). C opper requirements may be affected by breed. Ward et al (1995) indica ted that Simmental and Charolais cows are more likely to display signs of Cu deficiency than Angus cows. Factors such as crop management, climate and soil pH influence Cu antagonists Mo, Fe, and S, which are as important as forage Cu concentration in itself (MacPherson, 2000; McDowell and Valle, 2000). The low Cu status of ruminants can be derive d from a low forage Cu concentration, an elevated content of known Cu antagonist, or a combination of these two. High forage Mo is a commonly recognized contributor to Cu deficiencies in cattle (Suttle, 1991). Iron Most forages contain Fe concentrations cons iderably in excess of the requirements of herbivorous animals. Iron content of forage s is highly variable ranging from 70 to 500 ppm DM (NRC, 2000). The variation in Fe concentrations ca n be caused by soil contamination. Water and ingested soil can be significant sources of Fe for beef cattle. The forage concentrations of Fe depend on the plant species, the type of soil on which the plants grow as well as the degree of cont amination by soil. Acid soil conditions favor increased availability and plan t uptake of Fe. Forage Fe content is also affected by changes in soil conditions, climate and stage of growth of plants. Legumes generally contain more Fe than grasses and may cont ain 100 to 200 ppm DM Fe (Kabata-Pendias and Pendias, 1992). The seeds of legume plants ar e invariably richer in Fe than the cereal grains, which normally contain 30 to 60 ppm Fe (Underwood, 1981). The Fe requirements for beef cattle are recommended at 100 ppm DM (McDowell, 2003). Iron deficiency in grazing beef cattle is unlikely becaus e the forages contain more Fe than is necessary to meet the requirem ent, well over two times the requirement from

PAGE 48

37 forages. Dietary Fe content in the range of 250 to 500 ppm has caused Cu depletion in cattle. Excess dietary Fe (>100ppm) will have de trimental effect on the bioavailability of other minerals. High Fe intake due to high forage Fe, influenced by high soil concentration, has also been implicated in reducing Mg absorption in cattle. In areas where drinking water and forages are high in Fe, dietary Cu may need to be increased to prevent Cu deficiency (McDowell, 2003). Zinc The recommended requirement of Zn for b eef cattle is 40 ppm (DM), although Zn requirements of beef cattle and requirements for reproduction are not well defined. Often this requirement is not met for grazing cat tle (McDowell, 2003). The Zn content of forages is affected by a number of factors in cluding plant species, plant maturity and soil Zn (Minson, 1990). A relatively large portion of Zn in forages is associated with the plant cell wall (Whitehead et al., 1985). Most forages are marginal to low in Zn concentration compared to the suggested requirement le vel. Minson (1981) reported that tropical forages were slightly higher in mean Zn contents than temperate ones. Legumes are generally higher in Zn than gr asses. Whole cereal grains are relatively rich in total Zn. Cereal grains usually contai n between 20 and 30 ppm whereas the plant protein sources contain 50 to 70 ppm. The mean Zn concentration in pasture fo rages is 36 ppm and values vary widely (range 7 to 100 ppm), but a high proporti on lie between 25 and 50 ppm DM (Minson, 1990). The differences in Zn level between spec ies contribute little to reported variation in forages. The Zn concentrations of wheat, oats, barley, and millet generally lie between 30 and 40 ppm DM with slightly lower values common in corn and in all cereals grown on Zn-low soils, unless zinc-containing fert ilizers are used (U nderwood, 1962). Cereal

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38 straws generally contain only one third of the concentration found in the grain and are frequently less than 12 ppm DM (White, 1993). Poor drainage increases forage Zn but increased soil pH reduces Zn availability fo r the uptake of Zn in plants (Underwood and Suttle, 1999). Pasture fertilization with Zn in creases the element in plants. Hambidge et al., (1986) reported that cereal sp ecies fertilized with Zn ha d twice the con centration of this element than the plant species wit hout Zn application. Ge neral unthriftiness, excessive salivation, scabby skin on the le gs, slow wound healing, loss of hair and dermatitis over the entire body are the main deficiency signs of Zn. Manganese Manganese concentrations in forages ar e generally adequate but are variable depending on the availability of Mn due to plant species, soil pH and soil drainage (Minson, 1990). The Mn requirement for growing and finishing beef cattle is defined to be 20ppm DM, and breeding cattle require 40 pp m in the diet (McDowell, 2003). Forage Mn concentrations are generally well above the concentration suggested for the dietary requirement of cattle. Grasses tend to be considerably higher in Mn contents than legumes (Berger, 1996; MacPherson, 2000). Cer eal grains generally contain between 5 and 40 ppm DM and other plant protein sour ces normally contain 30 to 50 ppm. High levels of dietary Ca and P may interfer e with Mn metabolism causing the dietary requirement of Mn to increase (Hidiroglou, 1979). The acidity of the soil markedly influen ces Mn uptake by plants (Mitchell, 1957). Higher Mn concentrations are found in fo rages growing on acid soil (Cox, 1973). Poor drainage also leads to higher Mn contents in plants (Mitchell, 1963). No consistent trend in seasonal Mn concentrations has been repo rted (Minson, 1990). In most environments, Mn is not severely deficient. Identification of a Mn deficiency is difficult to determine

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39 due to the inconspicuousness of the deficiency signs. The signs of Mn deficiency are reduced reproductive performance in cows a nd crooked calf syndrome typified by weak legs and swollen joints in newborn calve s (McDowell, 2003). The maximum tolerable concentration of Mn is set at 1,000ppm DM (Church and Pond 1975; NRC, 1996). Cobalt The recommended concentration of Co in beef cattle diets is approximately 0.10ppm DM (Smith, 1987) with the range 0.08 to 0.12ppm. Forage Co concentration is dependant on the soil factors, plant speci es, state of maturity, pasture management, climate and soil pH. Cobalt concen trations in forages are also dependant on levels of Co in the soil (Ammerman, 1970). C obalt concentrations in pastur e plants and forages vary widely with the species and soil condition, though not with advancing maturity (Minson, 1990). Cereal grains are poor sources of Co w ith concentrations usually within the range of 0.01-0.06 ppm (Field et al., 1988 ). Forages legumes are generally higher in Co than in grasses (Singh and Aruna, 1994; Greene et al., 1998). Differences among grass species exist in the degree to which they are contaminated with soil a nd in their ability to absorb Co from the soil (Jumba et al., 1995). Cobalt requirements are higher when cattle are fed high grain diets (McDowell, 2003). Soil pH is th e major determinant in the availability of Co and some soils are deficient in this element (Underwood, 1981). Cobalt uptake by plants is decreased as soil pH increases (B erger, 1995). Increasing soil pH from 5.4 to 6.4 reduced the Co content of ryegrass from 0.35 to 0.12 ppm (Mills, 1981). Higher pH encourages the establishment of better qual ity grasses of lower Co content (MacPherson, 2000). The problem of Co leeching from the topsoi l by heavy rainfall is often aggravated by rapid growth of forage during the rainy se ason, which dilutes the Co content. The soil

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40 water logging allows th e release of Co from the soil mine rals into soil solution, so that the forage on poorly drained soil can have up to seven times more Co than that from well drained soils (MacPherson, 2000). High soil Mn is known to reduce Co uptake by forages (Adams et al., 1969; Norrish, 1975). Forages ar e deficient in Co concentrations for grazing cattle in many parts of the world (McDowell, 1985). Young and rapidly growing cattle seem more susceptible to Co deficiency than mature cattle. Cobalt toxicity is not likely to occur because cattle can tole rate approximately 100 times the dietary requirement. Molybdenum Forages vary greatly in Mo concentra tions, depending on both soil type and soil pH. Soil Mo can vary from 0.1 to 20 ppm DM and approximately 10% of soil Mo is normally available to the plant, but the propor tion rises with increasing soil pH resulting in elevated concentrations in crops and forages (Berger, 1995; Greene, 2000). Cereal grains and protein supplements are less vari able than forages in Mo. Cereals rarely contain more than 1ppm DM Mo, but there is a wide variation in forage Mo levels depending on soil conditions. Legumes and thei r seeds are the richest source of Mo and have most variable contents of Mo (0.5 to 1.5 ppm DM). Grasses cont ain generally 0.2 to 0.8 ppm DM Mo and cereal gr ains contain 0.2 to 0.5 ppm. Neutral or alkaline soils, coupled with high moisture and organic ma tter, favor forage Mo uptake (McDowell, 2003). Excessively high forage Mo levels (100 to 200 ppm) occur naturally only on alkaline soils. Liming of soil raises soil pH from 6.0 to 6.5, thereby increasing the forage Mo content two or threefold (McDowell, 1985). The maximum tolerable concentration of Mo has been estimated to be 10 ppm DM (NRC, 2000). Molybdenum in forages is read ily absorbed and may interfere with Cu

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41 metabolism in cattle. The Mo from dried forage s may not be available as that from green forage, since forages that interfere with Cu metabolism when grazed do not cause difficulties when fed as dry forage. Molybde num deficiency does not occur in cattle under practical conditions. High concentrations of Mo can cause toxicity. Diarrhea, anorexia, loss of weight, stiffness and changes in hair color are the signs of Mo toxicity (Underwood and Suttle, 1999). Selenium Selenium concentrations in forages vary greatly and depend primarily on the Se content of the soil and the parent materials fr om which it is obtained (Doyle and Fletcher, 1977). Forages produced in certain geographi cal regions are extremely low in Se (0.05ppm), whereas forages produced in othe r regions can act as Se accumulators (>300ppm). Forage species commonly used for grazing livestock can ha ve low Se levels, but they sometimes have toxic concentrations as well when grown on seleniferous soils (Hamilton and Beath, 1963). Tropical legumes have lower Se contents than tropical grasses (Long and Marshall, 1973), and grasse s generally contain more Se than legumes at all levels of soil and fertilizer Se (Davies and Watkinson, 1966). However, the difference diminishes as soil Se status d eclines (Minson, 1990). Pasture and forage concentrations of Se can be below 0.05 ppm DM and may be as low as 0.02 ppm in areas of low Se soils (Whelan et al., 1994). Se conten ts of cereal grains ar e widely variable and wheat grain may be higher in Se than barley and oats (Miltimore et al., 1975). Forages grown on sandy soils tend to have low Se, and lower on mineral upland soils than on organic moorland soils. Li ndberg and Lannek (1970) reported that the annual changes in mean temperature can also affect Se content of forage. Higher rainfall in some areas may also have an effect in re ducing Se contents of forages (Reuter, 1975).

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42 The beef cattle requirements can be me t by 0.1-0.2 ppm DM. Selenium deficiency reported in beef animals receiving forage s containing 0.02 to 0.05ppm DM (Hidiroglou et al., 1985; Spears et al., 1986) resu lts in degeneration of muscles (white muscle disease) in young animals and the signs are stiffness, lameness and possible cardiac failure. The maximum tolerable concentration of Se has been estimated to be 10 ppm DM (McDowell, 2003). However, it is recommende d that excess Se supplementation should be avoided unless known deficiencies occur. Liver Minerals The liver is the metabolic center of minerals in the body. The mineral status of animals is best described for some trace mi nerals by concentrations in the liver. The differences in correlation coefficients between concentrations of certain trace minerals in blood and liver are higher in deficient animal s because endogenous reserves are depleted. McDowell et al. (1986) indicated that liver, taken either by biopsy or from sacrificed animals, is an excellent indicator of the st atus of certain trace elements. Liver biopsies can be performed on large ruminants with litt le difficulty to the researcher and minimal risk to the animal. Liver biopsy samples from live animals may provide a more reliable source for diagnosing sub-clinical mineral de ficiencies for certain trace minerals if adequate sample numbers are collected. T oo few samples may be misleading and not a true representation of herd trace mineral status. Copper The liver is the central organ of storage for Cu and it regulates Cu metabolism very effectively (OÂ’Dell, 1984). Liver Cu concen tration provides a useful index of the Cu status in livestock. Underwood (1981) indicated that normal liver Cu values vary from

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43 100 to 400 ppm DM. A decline in elemental liv er Cu manifests Cu deficiency while toxicity causes liver concentration to incr ease (McDowell, 2003). Cunha et al. (1964) indicate d that the liver Cu cont ent in cattle with good Cu nutrition status be between 100 and 300 ppm DM . The liver Cu contents of 317 ppm for the summer-fall season and 250 ppm for the wi nter-spring season were reported from Florida by McDowell et al. (1989) . Copper values of 75 ppm DM could be considered as marginal while values below 25 ppm often resu lt in severe clinical deficiency signs (McDowell, 2003). The concentra tions of liver Cu are influe nced by a number of dietary factors. Copper requirements are increased by dietary Mo and S and the antagonistic action of Mo is exaggerated when S is high (NRC, 1996). Molybdenum and S interfere with Cu absorption in the rumen by forming thiomolybdates that bind Cu resulting in compounds that cannot be absorbed by the animal (Gooneratne et al., 1989; Spears, 1991). Decreased liver Cu levels can be caused by excessive Fe in the diet (Bremer et al., 1987). High intakes of Zn and calcium car bonate also influence the liver Cu concentrations (McDowell, 2003). Iron The two compounds, ferritin and hemosiderin, are the predominant storage forms of body iron (Fe) (Morris, 1987). Ferritin is a non-haem protein (globulin) compound and its concentration in the tissues particularly in the liver, together with that of hemosiderin reflects the Fe status of th e animal (Hallberg, 1984). Hartley et al. (1959) reported that the normal level of Fe in liver ranges from 180 to 340 ppm DM. Ammerman (1970) reported live r Fe levels of 100 to 300 ppm DM in Florida cattle in adequate state of Cu nutrition. Liver Fe is closely related to Cu status and the normal Fe concentration in liver is between 200 and 300 ppm DM (Cunha et al.,

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44 1964). McDowell et al. (1980) suggested values le ss than 180 ppm DM as a critical level, and they later found that cattl e in southwestern Florida ha d liver concentr ations of 283 ppm DM in the wet season and 105 ppm in the dry season. Salih (1984) found liver Fe values of 653 ppm for the wet season and 548 ppm in the dry season. Hedges and Kornegay (1973) reported that liver Cu c oncentration was decreased from 505 to 113 ppm by increasing the dietary Fe levels from 101 to 312 ppm in cattle. Rosa et al. (1982) found that high dietary zinc reduces Fe storage. Manganese Manganese is distributed in very low concen trations in the cells and tissues of an animalÂ’s body. According to NCMN (1973), live r tissue seems to be the most promising criterion for assessing the Mn status of animals. Highest co ncentrations of Mn are found in liver, hair and skeleton (ARC, 1980). The nor mal level of Mn in cattle liver is in the range of 8 to 10 ppm and concentrations below 8 ppm indicate deficiency (Underwood, 1977). Egan (1975) reported that values below 6 ppm of liver Mn result in deficiency signs. Watson et al. (1973) found that increasing dietary Mn concentrations in feed elevated liver levels. From Florida, McDo well et al. (1989) found liver Mn levels in cattle of 11.5 and 10.5 ppm for the summer-f all and for the winter-spring season, respectively. McDowell et al. (1985) concluded that liver Mn value of 6 ppm is accepted generally as a critical level. Cobalt The liver Co status can be assessed by either determining elemental Co concentrations or analyzing vitamin B12. Conrad (1978) suggested th at liver Co content is sufficiently responsive to changes in Co intake . The liver, bone and h eart have the highest

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45 concentrations of Co, and liver vitamin B12 concentrations, however, are more sensitive and reliable than liver Co (Smith, 1987). Am merman (1981) indicated that a decrease in liver Co and vitamin B12 are indicative of a dietary Co deficiency. Liver Co concentrations in the range of 0.05 to 0.07 ppm DM or below are critical levels indicating deficiency (McDowell, 1997). Cunha et al . (1964) reported that normal levels of liver Co should be 0.2 ppm DM wh ile levels of 0.07 ppm should be considered borderline and 0.04ppm as a severe Co defi ciency. Under Florid a conditions, Salih (1984) found liver Co values of 0.63 and 0.43 ppm DM for the wet and dry seasons, respectively. Underwood (1981) indicates that normal healthy animals have liver Co concentrations, ranging from 0.2 to 0.3 ppm DM . Cobalt deficiency is associated with specific soil types and is observed in all climatic zones. Molybdenum Molybdenum concentrations in the liver reflect the dietar y contents of the element when Cu and S contents remain constant within the normal ranges (Mills and Davies, 1987). Xanthine oxidase, a Mo containing meta lloprotein, is present in liver in high concentrations and is essential for the meta bolic degradation of purines to uric acid. Underwood (1977) indicated that normal liver co ncentrations of Mo are 2 to 4 ppm DM. McDowell (1997) suggested that the critical liver Mo con centration is 4 ppm DM and levels above 4 ppm DM are in dicative of excess. The excess dietary Mo interferes with Cu metabolism and leads to clinical signs of Cu deficiency (Ma ynard et al., 1979). Salih (1984) found that mean liver Mo contents were 3.0 an d 2.6 ppm during the wet and dry seasons in south Florida, respec tively. The main concern in Mo nutrition is toxicosis associated with high dietary Mo inta ke. The manifestations of clinical signs of Mo toxicosis in cattle are diarrhea, anor exia, achromotrichia and posterior weakness

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46 (NRC, 1980). Molybdenum toxicity generally occurs in cattle grazing pastures with 20 to 100 ppm Mo but not in cattle grazing normal past ure of 3 to 5 ppm Mo or less. Both Mo toxicosis and Cu deficiency are generally corrected by providing additional Cu to the animal diets (McDowell and Conrad, 1991). Selenium Selenium status in animals is best reflected by concentr ations of the element in blood and liver (Langlands, 1987). Underwood (1977) reported that liver and kidney contain high concentrations of Se and they are very sensitive to dietary Se changes. Conrad (1978) suggested that liver Se concentrations greater than 0.1 ppm are considered as normal. In a Florida study, McDowell et al. (1989) found liver Se contents that ranged from 0.34 ppm in the wet season and 0.33 ppm in the dry season. The concentration of 0.25 ppm DM is liste d as the critical level for liver Se (Andrews et al., 1968; McDowell, 1997). A deficiency may resu lt in muscular dystrophy, stiffness in the limbs, inability to stand, de pressed growth, infer tility and sudden death (Langlands, 1987). Liver levels above a range of 5 to 15 ppm indicate a possible toxicity. Selenium toxicity is associated with seleni ferous soils, the consumption of some plant species, which accumulate Se, and sometimes with the excessive administration of Se supplements. Blood Plasma Minerals Body fluids such as blood and blood compone nts are usually easily obtained from animals without causing injury and can be analyzed for mineral concentrations. The mineral contents in whole blood and its com ponents are frequently used because they are correlated to nutritional stat us, particularly for Fe, Se and Zn. However, blood concentrations of most minera ls change rapidly and are in fluenced by many factors other

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47 than dietary supply such as calving, lactation and other sour ces of stress or disease. Therefore, blood concentration of any mineral shoul d be interpreted with caution and in conjunction with other assessmen t criteria. Underwood (1981) indicated that the mineral values in blood plasma or serum, which are consistently and signifi cantly above or below the normal concentrations, provide suggestive but not conclusive ev idence of a dietary deficiency or excess of a particular mineral. Calcium and Phosphorus Cunha et al. (1976) from Fl orida, indicated that mean plasma Ca levels of 10-12 mg/100 ml is normal for healthy cattle, while levels below 8 mg/100 ml (80 ppm) are suggestive of a calcium deficiency. U nderwood (1981) considered that blood plasma is a good indicator of the Ca status of the grazing animals and the normal concentrations of Ca in blood plasma were 9-11 mg/100 ml. Benzie et al., (1955) reported that blood Ca concentration reflected dietary Ca and physio logical status of the animal. Phosphorus status of grazing animals can be determ ined by blood inorganic P levels. The normal values of plasma P are 4.5 to 6.0 mg/100 ml for adult animals and somewhat higher (6 to 8 mg/100 ml) for very young animals.. Plasma P level can be a good indicator of status in ruminants only if stress factors, sampling ti me and proper blood preparation are carefully controlled (McDowell, 1985). The first known response to a dietary defici ency of P is a fall in the inorganic P fraction of the blood plasma and a withdrawal of Ca and P from reserves in the bones (Underwood, 1981). Plasma levels consisten tly below 4.5 mg/100 ml in cattle are indicative of P deficiency (McDowell, 2003). Th ere is usually a tendency for plasma P to rise in chronic Ca deficiency and for plasma Ca to rise in P deficiency, necessitating separate physiological contro l mechanisms for the two minerals (Field et al., 1975;

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48 Underwood and Suttle, 1997). Chicco et al., (197 3) reported that high Ca in the diet tends to reduce plasma P level and vice versa. In creasing inorganic phospha te in the plasma results in the formation of a colloidal Caphosphate complex that is rapidly removed from the circulation (Irving, 1973). An imbalance of the Ca to P ratio (2:1) and other dietary factors influence P absorption, retention and concentration in the plasma. Iron, Al, Mg, Zn, K, S, low dietary protein and low dietary energy have been reported to interfere with P absorption and retention (Cohen, 1975). Magnesium Serum Mg is a good indicator of Mg st atus of various species. Magnesium concentration in serum does not decrease unt il a significant deficiency is evident, suggesting the urine of animals a better in dicator (McDowell, 2003) . The NCMN (1973) indicated that Mg status of ruminants could al so be assessed from Mg contents in blood and urine. Underwood (1981) recommended the nor mal range of serum Mg in cattle to be 1.8-3.2 mg/100 ml, and found serum Mg concen trations below 1.7 mg/100 ml (17 ppm) in animals suffering from hypomagnesemic tetany. Kemp (1960) observed a significant positive correlation between serum Mg level and Mg content in forage. Serum levels are often found to be as low as 0.1 mg/100ml in calves showing Mg deficiency signs (McDowell, 2003). The critical level of Mg concentration in serum is set at 2.0 mg/100 ml (20 ppm). Values below this level are considered de ficient, and values below 1.0 mg/100 ml are extremely deficient (Georgievskii, 1981). Ma gnesium absorption is influenced by many factors. Reinhardt et al. (1988) reported factors that affect Mg absorption to include K, N, energy, increased fatty acids, wa ter and the organic acid content of the diet. Chicco et al., (1973) reported that high di etary Ca depressed Mg cont ent in bone and plasma and

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49 decreased Mg utilization. Conve rsely, high Mg in the diet reduced plasma Ca. Newton et al. (1972) indicated that hi gh dietary K in the order of 4.9% resulted in reduced absorption and retention of Mg and blood plas ma Mg. Fontenot et al. (1960) observed that a ration containing 33.3% protein and 1.35% K increased fecal Mg and decreased plasma Mg. An increase of N conten t in forage from 2.11-2.62% to 3.74-4.38% decreased Mg utilization, accordi ng to Stillings et al., (1964). Copper Copper concentrations in liver and plasma are good indicators of the status and the deficiency. Underwood (1981) suggested that whole blood or plasma Cu concentrations adequately reflect dietary Cu status, even though the normal ranges are widely variable. Ceruloplasmin, the major Cu protein of blood pl asma, is used in evaluation of Cu status. Ceruloplasmin estimations on blood serum provide advantages over whole blood or plasma Cu determinations (Todd, 1970). Davis and Mertz (1987) sugge sted that over 90 % of plasma Cu exists as ceruloplasmin. The ratio of ceruloplasmin to plasma Cu is a better indicator of Cu status in animal s than the plasma Cu concentration only (Mackenzie et al., 1997). Plasma Cu is influenced by dietary Cu levels, and is reduced by the low levels of Cu and high levels of Mo and S in the diets. In all species, values are influenced by age, the type of sample, pregnancy and disease. The normal range of plasma Cu con centration is betw een 0.60 and 1.50 ppm (Underwood, 1981; McDowell, 1992). Accordi ng to NCMN (1973), the plasma Cu values consistently below 0.60 pp m are indicative of de ficiency in ruminants. Plasma Cu concentration of less than 0.60 ppm is consider ed slightly deficient, while levels below 0.40 ppm are clearly deficient. Cunha et al . (1964) reported that a normal blood Cu concentration in the healthy mature bovine is 0.75 to 1.00 ppm. Blood Cu level is well

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50 correlated with liver Cu under deficient condi tions. However, high Cu level in liver was found to be not correlated with blood Cu (Hartmans. 1974). Plasma Cu levels of 0.50 ppm or less indicates a low liver Cu. When Cu intakes of animals are less than physiological needs, concentrations of Cu a nd activities of ceruloplasmin in plasma are not consistently reduced until liver Cu is le ss than 40 ppm (Claypool et al., 1975; Mills, 1987). Plasma Cu and ceruloplasmin levels are decreased by dietary Mo, which also depresses superoxide dismutase (SOD) activity (Ward et al ., 1997; Underwood and Suttle, 1999). Large intakes of Zn also reduce co ncentrations of Cu in plasma and liver of ruminants (Kellogg, 1990). Iron Iron in blood plasma is bound in the ferric state (Fe3+) to a specific protein called transferrin. Transferrin is the carrier of Fe in the blood and is saturated only to 30-60 % of its iron-binding capacity. Beard and Dawson (1997) suggested that for Fe overload, plasma Fe, transferring saturation and plasma ferritin are fairly good diagnostic criteria. The critical level of Fe concentration in plasma is recommended at 1 ppm (McDowell, 1985). A high positive correlation between seru m ferritin concentrations and body Fe stores exists, so that its estim ation is a useful indicator of iron status (Baynes, 1997). The concentration of Fe in plasma-bound transfer rin is reduced, but the level of transferrin itself is increased (Hallberg, 1984). In rumina nts, Fe deficiency can be assessed using reduced transferrin saturati on (<13% to 15%), serum Fe (<1.1 ppm) and hemoglobin levels (<10g/dl) (McDowell, 1976). There are few reports of Fe de ficiency in grazing animals. However, conditions involving severe blood loss, such as parasite infestation, which may cause Fe deficiency, may cause severe anemia (Underwood, 1981).

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51 Zinc Zinc concentrations in blood plasma or seru m are the most widely used indicator of Zn status of the animal.. Serum or plasma Zn values must obviously be used with caution in the diagnosis of Zn deficiency in farm an imals. Zinc status of cattle can be assessed from the concentration of Zn in the diet and in plasma (NCMN, 1973). Zinc level in the plasma responds very rapidly to the alterati on of Zn contents in the diet. The NCMN (1973) has considered 0.60 to 1.4 ppm Zn in plasma as normal level and less than 0.40 ppm as deficient. However, there is usually a marked fall in plasma Zn in cows during and immediately after parturition (Goff and St abel, 1990). The critical level of plasma Zn is suggested to be at 0.80 ppm (McDowe ll, 2003). King (1990) suggested a combination of plasma Zn and metallothionein concentrations to determine Zn status. Both these are reduced when dietary Zn supply is low. Serum or plasma Zn may drop from normal levels of 0.80 to 1.2 ppm to concentrations of 0.15 to 0.20 ppm when Zn deficient diet is consumed. Mills et al. (1967) reported that in cases of a very low dietary Zn for ruminants, there is an immedi ate sharp decline in plasma Zn with reductions in feed intake and cessation of growth within less than one week. Conrad (1978) stated that Zn levels in plasma and serum can be markedly reduced in cases of severe Zn deficiency. Spears ( 1989) suggested that occu rrences of marginal Zn deficiencies are very common and widespread. Engle et al. (1997) reported a reduction in growth before any fall in plasma Zn in heifers. Plasma Zn values are particularly susceptible to st ress (Corrigall et al., 1976). We gner et al. (1973) reported that hyperthermic stress has a depressing e ffect on plasma Zn in cattle. Microbial infection due to Zn deficiency also decrease s plasma Zn in ruminants (Orr et al., 1990). Spais and Papasteriadis (1974) reported that under Greek conditions, cattle seriously

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52 affected with lesions had plasma concentra tion of 0.40 to 0.60 ppm and animals with very mild signs of deficien cy had 0.60 to 1.00 ppm. Selenium Selenium concentrations in plasma are less than half the concentration in erythrocytes but responds more rapidly to changes in Se intake. Plasma Se is the preferred measure of Se status in cattle (Stevens et al., 1985; Ullrey, 1987) particularly after a recent change in Se nutrition (Thompson et al., 1991). Selenium concentrations and glutathione peroxidase (GSH-Px) activitie s in tissues reflect dietary Se supply and may correlate well with concentrations in blood (Ullrey, 1987) depending on the duration of deprivation. Liver and plasma Se and GS H-Px activities increas e or decrease rapidly during Se repletion or depleti on, therefore the concentrations of the enzyme serve as an accurate indicator of Se sufficiency. Plasma Se is considered to be a good overall status indicator and levels below 0.03 ppm indicate a clear defici ency in cattle (McDowell, 1997). The normal range of Se concentra tions in plasma is 0.03 to 0.1 ppm. Growing cattle can tolerate exceedingly lo w blood Se concentrations when they graze continuously (McDowell, 2003). Perry et al . (1976) reported that plasma Se levels in steers reflected the dietary le vels administered in different treatments of diets. Jukola et al. (1996) suggested that approximately 0.08 ppm in plasma is required based on preventing mastitis. Sunde (1997) observed that GSH-Px activity decreases in deficiency and the activity is rest ored upon supplementation. Mineral Status of Soils Pasture forages often are the sole component of a grazing animalÂ’s diet. For this to be possible, it is necessary for the forage plants to have good soil and climate conditions for their development in order for them to produce high dry matter yields of excellent

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53 quality. In this situation, th e plants withdraw from the soil solution the essential mineral elements in quantities to satisfy their own requirements as well as satisfying many of the requirements of grazing livestock (Black, 1968) . Beef cattle depend almost exclusively on these forages to derive their total mine ral requirements. In a given soil, plant absorption of elements occurs in quantities proportional to its concentration in the soil solution when these are not excessive in re lation to the capacity of absorption by the plants. Therefore, in accordance with the requ irements of the plant, elements with low, high, or excessively high concentrations in the soil solution yi eld plants with a deficiency, sufficiency, or toxicity of the el ement in question. The deficiency or toxicity of an element provokes imbalances in the abso rption of other elements and in both cases the plant growth is reduced (Cor ey and Schulte, 1972; Carson, 1974). Plants with deficiencies or toxicities are unhealthy and constitute pastures of low nutritive value for animals and often result in yields of lower dry matter than the genetic potential of the species. Even when animals ingest normal quantities from these pastures they will often be deficient in minerals and other nutrients. Consequently, the quantity and quality of the nutrients produced in the pa sture depend directly on the availability of the essential elements which are available to the plants from the soil (Corey and Schulte, 1972). Most mineral deficiencies in grazi ng animals occur on in fertile soils under extensive systems of grazing management a nd are often accompanied by deficiencies of energy and protein (McDowell et al., 1984). In fertilized pastures, th e concentrations of Ca, P, and K are mainly influenced by fe rtilizer applications (Jones and Wilson, 1987). Mineral composition of forage plants is a ffected by soil-plant factors including soil pH, fertilization, drainage, plant maturity and plant species, as well as interaction among

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54 minerals (Gomide, 1978; Reid and Horvath, 1980). Mineral concentr ations in plants generally reflect the adequacy with which the soil can supply absorbable minerals to their roots. Plants rapidly take up minerals during early growth. But, as growth accelerates, dry matter accumulates more rapidly than minera ls are taken up, with the result that the content of most minerals decrease wi th advancing maturity (McDowell, 2003). Invariably, higher concentration of minerals in the leaves than the stem contributes to the decline with age as proporti on of leaf in the forage d ecreases (Jones and Wilson, 1987). The yield of plant, as well as its mineral content, is affected by soil mineral status. Different species and strains of plants can vary greatly in mineral composition, even when growing on the same soil. The climatic and seasonal conditions, as well as stage of growth, affect the mineral composition of plants and the chemical form of mineral in soil, soil pH and degree of aeration or waterloggi ng influence the availability of some soil minerals (Underwood and Suttle, 1999). Macrominerals Mineral deficiencies manifested in gr azing animals are ofte n associated with specific regions and are direc tly related to soil characte ristics (McDowell, 2005). The Florida soils are typically aci dic, infertile and sandy in te xture with the exception of organic soils at some areas (Fiskel and Zel azney, 1972). The pH levels can be lower than 5.5 and the presence of exchangeable aluminum in the soil leads to soil acidity problems (Sanchez, 1981). Increasing the pH by liming of the soil is the best corrective measure. Above pH of 5.5, soil Ca conten t is generally adequate fo r pasture growth of most species. Poor growth and herbage production on acid soils (below pH 5.5) are caused by excesses of soluble Mn, Fe, and/or Al rather than Ca content (War ncke and Robertson, 1976). Beeson and Matrone. (1976) reported that low availability of soil P may be due to

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55 soil acidity or alkalinity resul ting in the formation of Al or Fe complexes with phosphate. In general, soils containing more than 30 ppm of available P are normal (Gomide, 1978). In most grazing areas of tropical countries soils and plants are low in P for the most of the year, and mature forages contain less than 0.15% P (McDowell et al., 2003). Gomide (1978) indicated that most soils, particularly clay an d organic soils, are relatively high in K while sandy soils are frequently deficient. Soil containing K concentration between 80 and 120 ppm is c onsidered to be adequate (Warncke and Robertson, 1976). Forage K concentration changes during growth for physiological reasons independent of the soil K level (G rimme, 1976). Normal K content in forages ranges from 1.0 to 2.5% dry matter. Cuesta et al. (1993) obser ved that plant K concentrations may vary throughout the grow ing season and be deficient at times. The plant uptake of Mg depends on the amount present, the degree of saturation, the nature of other exchangeab le ions and the type of soil (Tisdale et al., 1993). Metson (1974) stated that the amount of Mg in the so il is strongly influenced by the process of weathering. Many tropical acid soils are relatively poor in Mg without having Al toxicity problems (Sanchez, 1981). Breland (1976) re ported Mg soil concentrations from 0-9.1 ppm as low, 9.2-21.1 ppm as medium, and above 21.2 ppm as high, using the double acid extraction method of analysis for Florida soils. Sodium in soils in high quantities is restrict ed to arid and semi-arid regions (Tisdale et al., 1993). Sodium is one of the most loosel y held of the metallic ions and Na ions are not subject to covalent bonding and are less tightly bound to cation exchange sites than Ca, Mg or K. Thus, Na is readily lost th rough leaching. Merkel et al. (1990) reported a soil Na concentration of 9.6% for the northern region of Florida. Forages are in general

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56 low in Na and a deficiency in forages is co mmon and inevitable. Sodium concentrations in the forages generally provide less than half of the requirements of grazing animals. Trace minerals Trace mineral availability from the soil to plants depends greatly on the soil pH. In general, as soil pH increases, the availab ility of Cu, Fe, Zn, Mn, and Co decreases. Molybdenum and Se availability however in crease with increasing pH (McDowell, 2003). Whole plant concentrations of trace mi nerals may increase, decrease, or show no consistent change with soil conditions in additio n to other factors such as stage of growth, plant species, and the season or climate of the particular region affecting plant concentrations. Plant genetics pl ay a unique role in mineral uptake, as wide variations in mineral concentrations have been observed in different forage species grown in the same soil (McDowell, 2003). Among the trace elements Cu is known to be the most deficient element in soils in many parts of the world. Copper in soils is us ually absorbed in the form of cupric ion (Cu+2) by plants (Tisdale et al., 1993). Factors that affect Cu content in soils include parent material, organic matter, clay conten t, and soil pH (McLaren et al., 1983). Copper is most soluble in acid soils and its solubi lity decreases as the pH increases. Copper has the tendency to concentrate in the surf ace horizon, bound to the soil organic matter and clay minerals (Thompson and Troeh, 1978). Soil Cu content ranges from 2 to 50 ppm, with a mean value of 20 ppm (Reid and Horv ath, 1980). Iron content in soils is highly variable. Viets and Lindsay (1973) suggested at least 2.5 ppm Fe in soils as critical. McDowell et al. (1982) reporte d extractable soil Fe cont ents ranged from 12.1 to 51.9 ppm, with corresponding values in forages we ll above the requireme nts for grazing beef cattle. Iron solubility declines with increasi ng soil pH. When the pH rises, for example by

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57 liming, both Fe(OH)3 and Fe(OH)2 precipitate due to increased concentration of OH ions in the soil. An increase in soil pH by liming reduces the availability of Zn to plants. Lindsay (1972) indicated that high soil pH a nd Ca reduces the availability of Zn. Zinc deficiency occurs mainly in acid and sandy so ils where leaching has reduced total soil Zn level. Olsen (1972) reported that Zn defici ency is observed frequently on high phosphate soils. From a Florida study, Street and Rhue (1980) reported total soil zinc ranging from of 10 to 300 ppm. The Mn uptake of plants is affected by soil acidity. A soil pH of around 4.0 is more favorable for uptake by plants. McDowell (2003 ) reported that Mn deficiency may occur after heavy liming, which reduces its availabi lity. Soil Mn concentrations vary widely, ranging from 20 to 6000 ppm (Street and Rhue , 1980). Variation of Mn contents of forages is due to species differences as we ll as soil pH and fertil izer effects (Underwood, 1977). McDowell et al. (1982) reported soil Co values ranging from 0.09 to 0.12 ppm for the fall season and from 0.12 to 0.26 ppm for th e winter season in a Florida study. Cobalt deficient soils and forages are a major pr oblem throughout the world. Becker et al. (1965), from Florida, reported that pastures with “salt sick” cattle had 0.000 to 0.035 ppm forage Co. The Mo content of soil, soil pH and s eason are the factors contributing to the variation in Mo concentrations in forages. Mo availability is high on alkaline soils (Kubota et al., 1967). Large (1971) observed that a soil level of at least 0.4 ppm Mo is adequate for most plants. Under Florida c onditions, forage Mo concentrations vary widely, as does Mo in soils. The Se contents of plants depend on soil factors, as well as plant species, maturity and yield (Ammerman et al., 1978). Soil factors that affect Se

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58 concentrations are the Se contents of host rock s, soil pH and nature of the drainage waters (Cooper et al., 1974). McDowell et al. (1982) suggested soil Se content of 0.2 ppm as the critical value.

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59 CHAPTER 3 MATERIALS AND METHODS Description of Research Two experimental cool season grazing studi es were conducted at the North Florida Research and Education Center (NFREC) of the University of Florida located at Marianna in Northwest Florida. These two st udies, each lasting two years, were carried out over four consecutive years from 2001 to 2005 during the winter-spring season for each year. Both studies were of a 2 x 2 f actorial design with th e purpose of evaluating two different annual pasture forages; small gr ains, (rye and/oats mix) with or without ryegrass for the first two years, and oats w ith ryegrass or ryegrass only for the last two years. The planting of these winter annuals as monocrops or in mixtures involved two land cultivation/planting methodsprepared seedbed (PS) and sod seeding (SS). For each year throughout both studies, eight 1.32 ha fenced pastures or paddocks were utilized for each study. The eight pastur es were divided into two groups, each with four pastures/paddocks numbered R5 to R8 and R9 to R12. The first four pastures (R5R8) were allotted for the sod seeding treatments (SS) and the other four (R9-R12) for the prepared seedbed treatments (PS). Each of the four forage/cultivation combination treatments were assigned to two pastures each year, thereby giving two replicates per pasture treatment per year. For the PS treatm ents, the four paddocks were prepared by deep plowing of the land followed by disc ha rrowing and the winter annuals were planted using a grain drill. In the four pastures assigned for sod seed ing treatments, a no-till seed

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60 drill was utilized and the forage treatments were planted directly into dormant bahiagrass (Paspalum notatum). Soil analyses were done every year for all th e pastures separately. Soil types, tested in July 2005, showed that the soils are dom inantly of Fuquay series associated with Orangeburg in most paddocks except paddocks R6 and R8 where Greenville series and Orangeburg dominates. These soils are well drained with a loamy sand surface and a sandy clay loam to sandy clay subsurface, and these soils are typically acidic in nature. Initial fertilization and liming rates were appl ied to the pastures ba sed on soil analyses that were done by a commercial laboratory (Waters Agricultural Laboratories, Inc, Camilla, Georgia), The planting dates used for various forage treatments were based on UF/IFAS recommendations. The SS pastures were not pl anted until after first killing frost on the bahiagrass. During the two years of wint er grazing Study 1 (i.e., 2001-02 and 2002-03), the cool season forage combinations, rye and/ oats mix (RO) and rye, oats, and ryegrass (RORG) were planted in late November for y ear 1 and early November for year 2 for the SS pastures. The RO in PS pa stures were planted in ear ly October and the RORG-PS pastures were planted mid to late October for each year. In year 1 of Study 1, the grazing period started from late January and earl y December after planting, in the SS and PS pastures respectively, and ended in late Apri l for year 1. In year 2, it was from mid February to mid May in the SS pastures (b oth RO and RORG), and from mid November to mid April for RO and from mid December to mid May for RORG in the PS pastures. For the winter-spring grazing season in the year 3 (2003-2004) during Study 2, the winter forage mixtures of oats and/ryegrass (ORG) or ryegrass (RG) were planted in mid

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61 November in the SS pastures and late Octobe r in the PS pastures. Gr azing was started in mid March the following year in the SS past ures and mid February in the PS pastures. Grazing ended in late April in both the SS a nd PS pastures. For the same study in year 4 (2004-2005), the forage combinations of ORG and RG were planted in early November in the SS pastures and mid October in the PS pastures. The animals were allowed to graze starting from mid January for ORG treatment and early February for RG treatment in the SS pastures, and late November for ORG treat ment and early December for RG treatment in the PS pastures. Grazing was stopped in late May the following year for the SS pastures and mid to late May for the PS pa stures. The length of grazing season averaged 81 and 139 days in the SS and PS pastures resp ectively in the first year of Study 1, and 97 and 139 days in the second year of Study 1. For Study 2, the grazing season was continued for 38 to 49 days in the SS pastures and 87 to 105 days in the PS pastures in year 3, and 106 to 134 days in the SS pastures and 112 to 166 days in the PS pastures in year 4 for ORG and RG treatments, respectiv ely. All pastures for all four years were grown under dry land conditions. These pastures were top dressed twice with nitrogen fertilizers, each time with 84 kg of N per ha, within each year. For each year within Study 1 and 2, 32 growing Angus and Angus crossbred heifers and steers for Study 1 and heifers only fo r Study 2 (Brahman/Angus cross, Simmental, Brangus, Angus/Brangus cross and Angus/Heref ord cross) were utilized. The animals’ initial body weight averaged 257 and 262 kg for year 1 and 2, and 289 and 250 kg for year 3 and 4, respectively. All cattle were allotted equally wi thin replicate into groups of four, known as “tester cattle”, based on sex, initial we ight, and genetic background. The treatments were assigned at random to the groups within replicate. The tester animals

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62 were allotted to their treatment groups upon init iation of grazing of the first pasture. The animal groups whose pastures were not rea dy were fed hay and supplement (80:20, corn: cottonseed meal) based on their body weight unt il their assigned past ures were ready to graze. The tester cattle were weighed before pasturing and the experimental period started. Three exclusion cages per pasture, about 1.2 m x 1.2 m x 1.2 m in size, were placed at representative locations within each pastur e just before start of grazing each year to provide an ungrazed area for forage sampli ng. Grazing was started when the forage was about 20 to 30 cm in height within pasture. Forage samples were collected from a square meter area within each cage at the start of grazing of the pastures and every two weeks until the end of grazing season. All years did no t have the same months represented due to differences in the start and end dates of the grazing season for each year. The start and end dates of grazing were different each year due to differences in planting dates that were due to differences in weather conditions and moisture availability during the grazing season. Grazing ended upon insufficient forage re-growth of the PS pastures and that of SS treatments were terminated upon the end of the last PS treatment within year, within study. The tester cattle were wei ghed every 28 days periodically as well as at the end of grazing periods. The weights were taken afte r fasting the animals overnight. Along with these groups of four animals, some extra cattle from the same calf crop as the testers were also used when available forage in the past ures was greater in qua ntity than the tester cattle could graze. The number and days these “put and take” cattle were used for each pasture was also recorded. A ll the animals were fed free-choice mineral supplement (F-R-M Wintergrazer Cattle Mineral, Flint River Mills Inc., Bainbridge, Georgia)

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63 recommended for beef cattle on pasture. The mineral mixture contained 7.00 to 8.40 % Ca (as carbonate), 4.00 % P (as phosphate), 14.00 % Mg (as oxide), and 19.00 to 22.00 % NaCl and provided per kg: 50 mg of Co (as car bonate), 500 mg of Cu (as sulfate), 50 mg of I (as iodate), 1 mg of Fe (as oxide), 2000 mg of Mn (as oxide), 26 mg of Se (as selenite), and 4000 mg of Zn (as oxide). Consumption was estimated at 30 to 80 g per head per day, which is within the range recommended by the manufacturer. Forage samples collected from the cages we re dried at 50 to 55° C, weighed, subsampled and ground in a Wiley mill to pass through a 2 mm stainless steel screen. The final sample obtained per pasture per sampli ng date was a pooled sample of the three sampling points per pasture. The dried weight taken was used to estimate forage dry matter yield of each pasture. The ground sample s were stored in plastic whirl-pak sample bags and saved for further analyses. A por tion of each sample was submitted to the Forage Evaluation Support Laboratory (FES L) of the Agronomy Department at the University of Florida to determine crude protein (CP) and in vitro organic matter digestibility (IVOMD) concentrations. The othe r portion was sent to the Animal Nutrition laboratory at the University of Florida for further preparation and mineral analyses. The forage samples were further pooled by m onth before analyses at the laboratory. The forage samples were analyzed for both macromineral and micro or trace mineral concentrations (Table 3-1). The sample s were ashed and solublized in nitric acid (HNO3) (final acid concentra tion approximately 5%) usi ng the method described by Miles et al. (2001). The concentrations of fo rage macrominerals, calcium (Ca), sodium (Na), potassium (K), and ma gnesium (Mg) and microminerals, copper (Cu), iron (Fe), zinc (Zn) and manganese (Mn) were determ ined by atomic absorption spectrophotometry

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64 (AAS) on a Perkin-Elmer AAS 5000 (Perkin-Elme r, 1980). To insure the quality of data, the calibration standards were prepared simu ltaneously and the standard curves were recalibrated in the middle and at the end of each set of samples analyzed. In addition, to ensure the overall reliability of the analytical methods, a certified National Bureau of Standards (NBS) reference material (cit rus leaves SRM-1572), acquired from the National Institute of Standards and Technology (NIST, 1998) was included as an internal standard with all samples analyzed. For a gi ven run of samples, if analysis of NBS standard resulted in values outsi de the range specified for that reference material, the data was ignored and the instrument wa s recalibrated and samples redone. Table 3-1. Analysis performed on co llected samples; Studies 1 and 2. Elements analyzed Samples Macronutrients Trace minerals Forage Ca, P, Na, K, Mg CP, IVOMD Cu, Fe, Zn, Mn, Co, Mo, Se Liver Cu, Fe, Mn, Co, Mo, Se Plasma Ca, P, Mg Cu, Fe, Zn, Se Phosphorus (P) concentrations in the sample s were determined using a spectrophotometer at 660nm as described by Harris and Popat (1954 ). Forage selenium (Se) was determined using the fluorometric method described by Wh etter and Ullrey (1978). Forage samples for analyses of cobalt (Co) and molybdenum (M o) were sent to a pr ivate laboratory (PPB Environmental Laboratories, In c., Gainesville, FL). The samples were analyzed using Inductively Coupled Argon Plasma (ICAP) proce dure. Forage samples were analyzed for IVOMD by the IFAS Forage Evaluation S upport Laboratory (FESL) according to a modification of the two-stage Tilley and Terry (1963) technique by Moore and Mott (1974). Forage dry matter was determined by drying sample for 15h at 105 û C. Forage crude protein (CP) was determined by m easuring total nitrogen (N) on an Alpkem

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65 autoanalyzer (Alpkem Corporation, Clackamas , OR). For N analysis, forage samples were digested using a modification of th e aluminum block digestion procedure of Gallaher et al. (1975). Sample weight was 0.25g, catalyst used was 1.5g of 9:1 potassium sulfate (K2SO4): copper sulfate (CuSO4), and digestion was conducted for at least 4 h at 375 û C using 6 ml of sulfuric acid (H2SO4) and 2 ml hydrogen peroxide (H2O2). Nitrogen in the digestate was determined by semi-automated colorimetry (Noel and Hambleton, 1976). Forage CP was calculated by multiplying the concentration of N by the factor of 6.25. In year 4 (2004-2005) of winter-spr ing grazing season during Study 2, blood samples and liver biopsy samples were obtai ned from the 32 tester cattle on 03/31/2005 just before the breeding seas on of the heifers. Blood samples were obtained from the tester cattle by puncturing the jugular ve in and collecting th e blood into sodiumheparinized vacutainer tubes (Becton Dickin son, Franklin Lakes, NJ). These tubes containing the blood were centrifuged at 700 x g for approximately 20 minutes. Plasma was transferred to other small tubes and stored in an insulated container with crushed ice at collection site. These plasma samples were subsequently transported to the Animal Nutrition laboratory at the Un iversity of Florida. Upon arrival, plasma samples were frozen at -20 û C until further preparation and analyses. For analysis, the frozen plasma samples were thawed to room temperatur e and deproteinated using 1% lanthanum chloride (LaCl3) and 10% trichloroacetic acid (TCA) as described by Miles et al. (2001). Plasma concentrations of Ca, P, Mg, Cu, Fe, Zn, and Se were determined by the same methods as described for forages.

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66 Liver biopsy samples were obtained unde r aseptic conditions using a collection procedure described by Chapman et al. (1963). About 1-2 g we t liver tissue was collected from each of 32 tester animals. The bl ood on the sample was removed by placing the sample on a filter paper and liver was then transferred to a whirl-pak plastic bag for storage in an insulated container filled with crushed ice and transported to the Animal Nutrition Laboratory and subse quently frozen until ready to prepare for analyses. Upon thawing, liver samples were dried, we ighed, ashed and solublized in HNO3 (Miles et al., 2001). Liver Cu, Fe, and Mn were analyzed by the same procedures as described above. To ensure the overall reliability of the an alytical methods, certified NBS Bovine liver (SRM-1577b of NIST; 1998) standard was routin ely included in the test procedure. Only 12 samples of liver tissues, randomly selected, were analyzed for Se concentration by the fluorometric method previously described. Liver Co and Mo concentrations were obtained from PPB Environmental Laboratorie s for the same 12 samples as those for liver Se. The experimental design was a complete ly randomized block (2x2) design. The forage minerals, CP and IVOMD data were analyzed by SAS version 9.0 (SAS Inst, Inc., Cary, NC) PROC MIXED using a repeated meas ures model, where month is the repeated measure. The procedure estimated the vari ance and covariance of random effects and performed a test of hypothesis on the fixed effects of month, treatment, and month by treatment interactions for both Studies 1 and 2 in the case of forage mineral studies. For plasma and liver mineral data, the SAS proce dure performed the tests of fixed effects on treatments only (pasture forage type and la nd cultivation/planting method) as month was not involved.

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67 CHAPTER 4 MINERAL CONCENTRATIONS OF COOL SEASON PASTURE FORAGES IN NORTH FLORIDA DURING THE WINTERSPRING GRAZING SEASON: . MACROMINERALS AND FORAGE ORGANIC CONSTITUENTS. Introduction Annual cool season pasture forages typical ly provide high quality nutrition during the late fall to spring grazing season in the Southeastern USA when permanent warm season pastures are dormant. Cool season forage plants are generally hi gher in nutritional quality than warm-season species in both mi nerals and organic constituents. Mineral requirements of grazing beef cattle are dyna mic because of differences in pasture resources, forage mineral content, seas on, genetics, age of animal, and stage of production (Chenoweth and Sanderson, 2005). Forage mineral composition varies significantly and is affected by soil-plant factors, includi ng soil pH, drainage, fertilization, forage species, forage matur ity, and interactions among minerals (Gomide, 1978; Reid and Horvath, 1980). Mineral concentr ations in both soils and plants affect mineral status of grazing livestock (Tower s and Clark, 1983). North Florida is between subtropical and temperate climatic zones a nd the soils are acid, infertile and sandy in texture (Fiskel and Zelazny, 1972). It is a co mmon practice to plant cool season annuals, such as rye ( Secale cereale ), oats ( Avena sativa ), and ryegrass ( Lolium multiflorum ) to provide forage for grazing by beef cattle dur ing the late fall to spring period in the southern coastal plain region of the USA. These forages ar e planted during the fall season and can be seeded directly into dormant wa rm season pasture (sod seeding) or planted into a clean tilled, prepared seedbed. A pr ogram of study was designed to compare clean

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68 tilled and sod seeded pastures with two comb inations of cool seas on annual forages in regards to forage yield and quality, and we ight gain and total grazing days by grazing growing beef cattle over the winter-spring grazing season. The objective of this part of the overa ll study was to determine macro and trace mineral concentrations of cool season pasture forages of two combinations of rye, oats and/ or ryegrass from clean tilled or sod-s eeded pastures under gr azing conditions over four consecutive winter-spring grazing seasons (2001-2005) in North Florida. The present paper discusses the nutritional status of macrominerals and organic constituents while the following chapter (Chapter 5) will evaluate trace minerals. Materials and Methods Two experimental cool season grazing studi es were conducted at the North Florida Research and Education Center (NFREC) of the University of Florida located at Marianna in northwest Florida. These studies , each lasting two years, were carried out over four consecutive years from 2001 to 2005 during the winter-spring months of November through May. Both studies were of a 2 x 2 factorial experiment to evaluate two different pasture forage t ypes: small grains, (rye and oats mix) with or without ryegrass for the first two years (Study 1); a nd oats with ryegrass or ryegrass only for the last two years (Study 2). These winter a nnuals were planted by two pasture land preparation/planting methods, tilled or prepar ed seedbed (PS) and sod seeded (SS). For each year within each study, eight 1.32 ha fenced pastures or paddocks were utilized for grazing by growing beef cattle. Th e pastures were divide d into two groups of four pastures for the sod seeding treatm ents; and four for the prepared seedbed treatments. Each of the four forage and cu ltivation combination treatments was assigned to two pastures each year, thereby giving tw o replicates per pastur e treatment per year.

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69 The four pastures of the PS treatments were prepared by deep plowing followed by disc harrowing, and the annual pasture crops were pl anted using a grain dr ill. In the four pastures assigned for SS treatments, a no-till s eed drill was used and the pasture forage treatments were planted into dormant bahiagrass (Paspalum notatum) . Soil was analyzed every year for all the pastures separately. These soils are well drained with a loamy sand surface and a sandy clay loam to sandy clay subsurface, and are typically acidic in nature. Initial fertili zation and liming rates were applied to the pastures based on soil analyses by a commercial lab (Waters Agricultural Laboratories, Inc., Camilla, Georgia). The planting dates used for various forage treatments were based on UF/IFAS recommendations (October fo r PS and November for SS). Grazing was started when the forage was about 20 to 30 cm in height within pasture. Grazing ended upon insufficient forage re-growth of the PS pa stures. The SS treatments were terminated upon the end of the last PS treatment. All past ures over the four y ears were grown under dry land conditions. These pastures were top dressed twice with nitrogen fertilizers, each time with 84 kg of actual N per ha, within each year. For each year within Studies 1 and 2, 32 growing Angus and Angus crossbred heifers and steers for Study 1 and heifer s only for Study 2 (Brahman/Angus cross, Simmental, Brangus, Angus/Brangus cross a nd Angus/Hereford cross) were utilized. Animals had an average initial body weight of 257 and 267 kg for year 1 and 2, and 289 and 250 kg for year 3 and 4, respectively. All ca ttle were allotted equa lly within replicate into groups of four, known as “tester cattle ”, based on sex, initial weight, and genetic background. The treatments were assigned at random to groups within replicate within year. The tester animals were allotted to their treatment groups upon initiation of grazing

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70 of the first pasture. The animal groups whos e pastures were not r eady for grazing were fed hay (bermudagrass) and supplement (80:20, corn:cottonseed meal) until their assigned pastures were ready to graze. The tester cattle were wei ghed before pasturing and the experimental period started. While gr azing the tester cattle were weighed every 28 days periodically as well as at the end of grazing periods. Th e weights were taken after fasting the animals overnight. Along with these groups of four tester animals, some extra cattle from the same calf crop as the te sters, known as “put and take” cattle, were also used when available forage in the past ures was greater in qua ntity than the tester cattle could graze. The number and days the pu t and take cattle us ed each pasture were also recorded. All the animals were offere d free-choice a mineral supplement (F-R-M Wintergrazer Cattle Mineral, Flint River Mi lls Inc., Bainbridge, Georgia) recommended for beef cattle on pasture. The minera l mixture contained 7.00 to 8.40 % Ca (as carbonate), 4.00 % P (as phosphate), 14.00 % Mg (as oxide), and 19.00 to 22.00 % NaCl and provided per kg: 50 mg of Co (as carbonate ), 500 mg of Cu (as sulfate), 50 mg of I (as iodate), 1 mg of Fe (as oxi de), 2000 mg of Mn (as oxide), 26 mg of Se (as selenite), and 4000 mg of Zn (as oxide). Consumption was estimated at 30 to 80 g per head per day, which is within the recomm endation of the manufacturer. Three exclusion cages per pasture, about 1.2 m x 1.2 m x 1.2 m in size, were placed just before the start of grazing each year at representative locations within each pasture to provide an ungrazed area for forage samp ling. For each year of both studies, forage samples were collected from a square meter ar ea within each cage at the start of grazing of the pastures and every two weeks thereaf ter until the end of gr azing season. The start and end dates of grazing were different each year due to differences in planting dates that

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71 were due to differences in weather conditions and moisture availability during the winterspring grazing season. Thus, all years did not ha ve the same months represented due to differences as noted above. Forage samples collected from the cages were dried at 50-55° C, weighed, subsampled, and ground in a Wiley mill to pass through a 2 mm stainless steel screen. The final sample obtained per pasture per sampli ng date was a pooled sample of the three sampling points per pasture. The weight take n was used to estimate forage dry matter (DM) yield of each pasture. The forage sa mples were further pooled by month before analyses at the laboratory. The ground samples were stored in plas tic sample bags and saved for further analyses. A portion of each sample was submitted to the Forage Evaluation Support Lab (FESL) of the Agr onomy Department at the University of Florida to determine crude protein (CP) and in vitro organic matter digestibility (IVOMD) concentrations. The other part of the forage sample was sent to the Animal Nutrition laboratory at the Univ ersity of Florida for furthe r preparation and analysis. For analyses of macromineral concen trations, the samples were ashed, and solublized in nitric acid (f inal acid concentration approximately 5%) using the method described by Miles et al. (2001). Concentratio ns of forage macrominerals, calcium (Ca), sodium (Na), potassium (K), and magnesium (Mg) were determined by atomic absorption spectrophotometry on a Perkin-Elmer AAS 5000 (Perkin-Elmer, 1980). To ensure the overall reliability of the analytical methods, a certifie d National Bureau of Standards (NBS) reference material (citrus leaves SRM-1572) was acquired from the National Institute of Standards and Technology (NIST, 1998) included as an internal standard with all forage samples analyzed. Phosphorus (P) concentrations were determined using a

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72 spectrophotometer (Harris and Popat, 1954). In vitro organic matter digestibility was determined according to a modification of the two-stage Tilley and Terry (1963) technique by Moore and Mott (1974). Fora ge dry matter was determined by drying samples for 15 h at 105 û C. Forage crude protein was determined by measuring total nitrogen on an Alpkem autoanalyzer (A lpkem Corporation, Clackamas, OR) as described by Noel and Hambleton (1976). Forage CP was calculated by multiplying the concentration of N by the factor of 6.25. In year two of Study 2 (2004-2005) wint er-spring grazing season, blood samples were obtained from all 32 tester cattle on 03/ 31/2005, just before the breeding season of the heifers. Blood samples were collected by jugular venupuncture into sodiumheparinized vacutainer tubes and centrifuge d at 700 x g for approximately 20 min at the collection site. Plasma samples were frozen at -20 û C until analyses. Frozen plasma samples were thawed to room temperatur e and deproteinated using 1% lanthanum chloride (LaCl3) and 10% trichloroacetic acid (TCA) as described by Miles et al (2001). Plasma concentrations of Ca, P, and Mg were determined by the same procedures as for forages. Experimental design was a completely randomized block design. The data for each of the macrominerals, and CP and IVOMD we re analyzed by SAS version 9.0 (SAS Inst, Inc. Cary, NC) PROC MIXED using a repeated measures model, where month was the repeated measure. The procedure estimated the variance and covariance of random effects and performed a test of hypothesis on the fixed effects, month, treatment, and month by treatment interactions for both Studi es 1 and 2. For plasma minerals, the SAS

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73 procedure performed the tests of fixed effect s on treatments only (pasture treatment) as month was not involved. Results and Discussion The cattle grazing the pastures from wh ich the samples were taken gained on average 0.8 to 1.15 kg.head-1.day-1 through these studies. Animal performance results will be published elsewhere. Forage minerals Study 1 The level of significance on various eff ects and mean forage macromineral concentrations during winter-spring grazing season for Study 1 (2001-2002 and 20022003) are presented in Tables 4-1 and 4-2, resp ectively. Grazing year had an effect on the forage concentrations of P (P<0.01), K, a nd Mg (P<0.05), and no effect on Ca and Na. Pasture land preparation/planting method of sod-seeding vs. clean tilled or prepared seedbed, or pasture forage type (i.e. rye/oats or rye, oats /ryegrass) also had no effect (P>0.05) on macromineral concentrations for both years 1 and 2. There were no land preparation by forage type interactions (P>0.05) for St udy 1. However, month of the grazing season had a definite effect on the con centrations of Ca (P <0.01), Mg (P<0.05), P and K (P<0.0001), but not Na (P>0.05). There was no treatment by month interaction for any macrominerals. Mean forage Ca concentrations varied monthly from November to May. All the mean Ca concentrations were at or above the suggested critical leve l of 0.30% of diet dry matter for beef cattle (NRC, 2000). Calcium concentrations in the forages were highest early on during the grazing season, during the months of November and December, and then declined slightly and leveled out during late winter a nd spring months. The

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74 differences noted in Ca concentrations dur ing November and December and between the rest of the grazing season were significant (P<0.01). Forage Ca concentrations have been found to be influenced by soil temperature, being higher upon cool temperatures. Forages grown in temperate regions generally contain more Ca than those grown in the tropics (Minson, 1990). Nitrogenous ferti lizer application increases pasture Ca concentrations and the concentration decreases with adva ncing maturity (Underwood and Suttle, 1999). Mean forage P concentration varied fr om 0.32% to 0.47% between November and May. The suggested critical forage P concentr ation is 0.25% for beef cattle and this level is often present in high quality past ure forages (McDowell, 2003). Higher P concentrations were obtained during the wi nter to early spri ng grazing months of November to March compared with lower conc entrations in the months of April and May (P<0.0001). Cereal grasses are considered a good source of P and temperate forages generally contain more P than tropical fora ges (Minson, 1990). Cool season forages are high in P during early and during immature stag es of growth. Forage P concentration and digestibility declines with advancing ma turity and weathering (McDowell, 2003). Forage Na concentrations were all lower than the critical level (0.06%) for beef cattle (McDowell, 2003). Mean Na concentratio ns were uniformly low during the months of the grazing season, November to May. The different months in which Na contents were analyzed in forages had almost the sa me concentrations and were not significantly different (P>0.05). Similar low concentrations in forages were reported for winter-spring months (0.02-0.03%) by Salih et al. (1988) fr om central Florida. The Na content of forages varies considerably and cereal fora ges are fairly low in Na, containing 0.01 to 0.06%. (Minson, 1990). When not supplemented to beef cattle, Na can be a limiting

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75 nutrient in the diet. A dietary de ficiency of Na is most likel y to occur in rapidly growing young animals fed cereal-based diets or forages inherently low in Na, and in pastures fertilized with K (Morris, 1980; Re id and Horvath, 1980; McDowell, 1997). Mean forage K concentrations were much higher than the critical level of 0.70%, ranging from 2.3% to 4.2% in the experime ntal winter-spring grazing season months. Actively growing grasses are usually high in K, containing 1 to 5% (McDowell and Valle, 2000). Forage K concentrations were highest during the m onths of November, December and January, then decreased and le veled out during the months of February through April, and were lowest in May (P< 0.0001). Robinson (1985) indicated that cool season grass species maintain higher K concen trations than warm season species. Forage K concentrations are known to be influenced by stage of plant maturity, and forages at the early stage of maturity are consid erably higher in K (McDowell, 1985). Forage Mg concentrations were found to be above the crit ical level (0.20%) recommended for beef cattle requirement (McDowell, 2003). Mean forage Mg was highest in the month of Novemb er, declined gradually during the winter to early spring months of December to March, and then incr eased slightly and plateaued out during the rest of the grazing months of April and May (P <0.05). Mayland et al. (1976) reported that Mg concentrations of cool season forages, es pecially rye, are highe r than that of wheat. Magnesium concentrations in general decline as the plant matures. Seasonal variations in the concentration of forage Mg are ge nerally low (Minson, 1990). High dietary K decreases Mg absorption (Schonewille et al., 1999); therefore K levels of forages in the range of 4.0 to 5.0% will double the Mg requi rements of the grazing animals (Underwood and Suttle, 1999). When combin ed with the very high concen trations of forage K, low

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76 Mg forage may cause reduced Mg absorption in ruminants. Thus, high content of K and a marginal content of Mg in high quality cool season forages could predispose both lactating beef cattle and growing cal ves to grass tetany (McDowell, 2003). The level of significance of various eff ects, mean forage DM yield, and mean concentrations of IVOMD and CP for St udy 1 of winter-spring grazing season are presented in Tables 4-5 and 4-6, respectively. Mean forage DM yield was not affected by the year, land preparation, forages used, and land preparation by forage type interactions (P>0.05). Month, however, had a significant effect on the DM yield (P<0.0001). Mean forage IVOMD values were affected by bot h the year (P<0.0001) and land preparation (P<0.01), but not affected by either forage type or a land preparation by forage type interaction (P>0.05). Forage IVOMD was affected by month (P<0.0001). Forage CP means were not affected by the year, forage type, and land preparation by forage type interaction (P>0.05). However, land prepara tion (P<0.05) and month (P<0.0001) affected CP concentrations. Mean forage DM yields were highly variable among the winter-spring grazing months, ranging from 492 kg/ha to 1390 kg/ha. Forage DM yields were low in November, increased in December and then declined in January and February. Both March and April had the highest DM yields due to spring growth, compared with all other months of the winter-spring grazing season (P<0.0001). Due to increasing daily temperatures and lack of moisture, there wa s a rapid decrease in DM yields during the month of May. The late April to early June peri od in North Florida is generally a dry time of the year. In addition, below normal rainfa ll occurred during April and May, especially

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77 during year 1 of this study. The DM yields are typically moderate to high during the growing stage of young plants and also at the early stage of maturity in the forages. Mean forage IVOMD varied widely from 66% to 86% during the grazing seasons. Mean values were fairly high for early periods of the grazing season. Highest values were observed in February and the concentrations were over 80% for the months, November through March. The values decreased in Apr il and more so in May. The differences observed in IVOMD values during the months of November through March and the final two months of spring season, April and May, were significant (P<0.0001). The decline in forage digestibility may be caused by gradua lly increasing temperatures toward the end of the grazing season. Minson (1990) suggested that high transpira tion rate is a factor that contributes to low forage digestibility. This can possibly be explaine d by two factors: 1) forage plants develop a large vascular syst em to convey the larg e quantities of water passing through the plant (or), 2) plants may wilt whenever soil cannot supply sufficient water to meet the potential ev apotranspiration. The increase in maturity also results in increased fiber and lignin concentrations of fo rage species, thus decreasing digestibility. Forage mean CP concentrations were higher at all months throughout the season than the critical level of 11% for growi ng beef cattle (Minson, 1971; NRC, 2000). Mean concentrations varied from 17% to 34%. Hi ghest CP concentrations were observed in November, while the lower concentrations we re found during the last two months of the grazing season, April and May. Forage CP con centrations decreased gradually from the start to the end of the grazing season (P <0.0001). Crude protein c oncentrations were found to be higher from prepared seedbed pa stures than sod-seeded pastures (P<0.05), and no differences in concentrations between forage types were observed. Concentrations

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78 of CP in pasture forages thr oughout the grazing period are ofte n related to the availability of N from the nitrogenous fertilizers applied to pastures. Forage CP concentrations are greatly reduced by an increase in temperatures and forage maturity (McDowell, 2003). Study 2 Tables 4-1, 4-3, and 4-4 presen t the data for the levels of significance of various effects and forage macromineral concentra tions during the winte r-spring grazing season for Study 2 (2003-2004 and 2004-2005). Forage Ca , P, and Na concentrations were affected by the year (P<0.01). Forage concentr ations of macromineral s were not affected by pasture land preparation/plan ting methods, forage type, an d land preparation by forage type (P>0.05) except the forage type eff ect on forage Ca only (P<0.05). However month had a significant effect on the concentrations of all macrominerals except Ca. Forage Ca, K, and Mg concentrations were affected (P <0.01) by forage type by month interactions but P and Na concentrations were not (P>0.05). Unlike that observed in Study 1, mean fora ge Ca concentrations were below the critical level (0.30%) for one forage type ev aluated (oats/ ryegra ss), varying from 0.17% to 0.30%, November through June. Forages were de ficient in Ca concen trations in all the months of the grazing season except May in which mean Ca concentrations were just adequate. The reason for low Ca concentrations in forages pertinent to this forage type is unknown. For the other forage type evaluated (ryeg rass), forage Ca concentrations started lower than the suggested critical level dur ing the fall and winter months, November, December, and January, and increased above critical level during February, March and April, and then decreased to just below the cr itical level in May a nd June. Cereal forages and grasses are known to be low to modera te in Ca concentrations for ruminants

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79 (McDowell, 2003). Forage Ca concentrations are less affected by advancing maturity (Gomide, 1978). Forage P concentrations were above the crit ical level (0.25%) for both forage types, ranging from 0.33% to 0.47% DM. Phosphorus con centrations were highest for the first two months, November and December, decreas ed and leveled out in January through March, increasing slightly in April and May (P<0.0001), and decreasing again in June for both forage types. Underwood and Suttle (1999) st ated that the P status of forage plants varies widely and is influenced primarily by th e P status of the soil, the stage of maturity of the plant, and the climate. In most circumstances, P concentrations decline dramatically as forages mature (Gomide, 1978). Mean forage Na concentrations ranged from 0.03% to 0.05% DM and were below the recommended critical level (0.06%) for both forage types. Low concentrations of Na were observed in both November and June, a nd mean Na contents of 0.04% DM were present in forages for all the months in between (P<0.05). Reid and Horvath (1980) reported that the use of fert ilizers containing K depressed Na in forages due to the antagonism between K and Na. In most envi ronments, Na concentrations decline with plant maturity (Underwood and Suttle, 1999). Potassium concentrations averaged higher than the critical le vels (0.70%) for both forage types in all the months (McDowell, 2003). Mean forage K was high in November, increased in December and then started decrea sing gradually from January to June for both forage types evaluated. Month differences in concentrations were significant for both forage types (P<0.0001). Forage K concentr ations are influenced by the K status of

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80 the soil, the plant species and its state of maturity, and are reduced markedly as the season progresses (Reid et al., 1984; McDowell, 2003). Mean Mg concentrations for both forage types were all below the recommended critical level of 0.20% for all months. Mean forage Mg concentrations were marginally low in the month of November, declined further in the months from December to March, and increased slightly in the following mont hs, April through June for the oats/ryegrass pastures. Mean Mg levels from the ryegrass only pastures were maintained at 0.18% for the first two months of the s eason, were low in January and February, increased slightly in the spring months, March, April and May, and then decreased in June (P<0.01). Low forage Mg concentrations may result in gra ss tetany, a deficiency di sease affecting beef cattle grazing on lush immature grass esp ecially during early spring growth (MarchApril). Vogel et al. (1993) suggested in cas es of hypomagnesemia, or grass tetany, that the interaction of Mg, Ca, and K is important . They suggested a cation ratio, K/ (Ca+Mg) be used to estimate the risk of induced gra ss tetany with the ratio less than 2.2 for forage species to be safe against Mg deficiency. In this study, the K/ (Ca+ Mg) ratios were found to be higher than the above ratio in both fora ge types evaluated. This indicates a potential problem with grass tetany, especially for an imals that depend on forage without adequate mineral supplementation. Tables 4-5 and 4-7 present the levels of significance of various effects and mean forage DM yield and mean concentrations of IVOMD and CP for Study 2, respectively. Mean DM yields were not affected by y ear, pasture land prepar ation/planting methods, forage type and land preparation by forage type interaction (P>0.05). Month (P<0.0001) and forage type by month interaction had a significant effect (P<0.05) on DM quantity.

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81 Concentrations of IVOMD were affected by land preparation methods, forage types (P<0.05), month, (P<0.0001) and year, and both interactions did not have any effect (P>0.05) on IVOMD. The CP concentrations were significantly affected by year (P<0.01), month (P<0.0001), and forage types by month interaction (P<0.05). Mean DM yields were the lowest and fl uctuated greatly during fall and winter months, November through February. There wa s a large increase in DM quantity in the spring months, March and April for both fora ge types (P<0.0001). The month of May had low DM yields compared with previous mont hs and DM yields were reduced at the end of grazing period. The difference in DM yiel d among months of the grazing season and between different forage combinations was signi ficant (P<0.05). This suggests that cold temperatures coupled with high moisture re duce the quantity of DM and DM yield tends to be higher at the early stage of maturity of forage plants. Mean forage IVOMD concentrations were higher, varying from 85 to 88% of DM during the months of November through Februa ry and started to d ecrease gradually from March to April, and there was a sudden d ecrease in forage IVOMD in May (P<0.0001) for both forage types. Differences in digestib ility of grasses may be caused by changes in water availability, temperatur e, or light (Minson, 1990). As temperature increases toward the end of the season, there is a decline in forage digestibility. Increasing maturity and high rate of transpiration in plants contribute to low fora ge digestibility (Minson, 1990). Mean forage CP concentrations were all above the cri tical level of 11% throughout the winter grazing season for growing beef cattle. Higher CP concentrations were found in November for both forage types and CP c oncentrations decreased significantly from December to the end of May (P<0.0001). Lo wer CP concentrations of 13% and 12%

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82 were obtained in May for both forage t ypes. Minson (1990) indicated that CP concentrations tend to be higher in the wet season ve rsus the dry season. Water availability and temperature may be the cont ributing factors for higher CP concentrations since growth and nitrogen uptake are enhanced. Blood plasma minerals Mean concentrations of plasma macrominer als (Ca, P, and Mg) were not affected (P>0.05) by pasture land preparation/planting me thods, forage types, and their interaction (Table 4-8). Table 4-9 presents the mean plas ma concentrations of Ca, P, and Mg with standard error of means for both forage types evaluated. Mean plasma Ca concentrations for both forage types exceeded the suggested critical leve l of 80 ppm (McDowell, 2003). There were no differences (P>0.05) in plasma Ca concentrations due to forage types. Plasma P concentrations were also greater th an the critical limit of 45 ppm. Plasma P concentrations generally reflect adequate P le vels supplied by forage plants at all times and ample consumption of mineral supplem ents (McDowell, 2003). Mean plasma Mg was greater than the suggested minimum level (2 0 ppm) in both forage types. Plasma Mg is considered an excellent indicator of body Mg status (McDowell, 2003). Plasma Mg concentrations did not differ (P>0.05) between the two fora ge treatments. Forage macrominerals, Ca, P, K, and Mg in Study 1 and Na along with others except Ca in Study 2 were found to differ in concentrations by month. Forage Ca, P, K, and Mg concentrations were adequate for gr azing beef cattle thr oughout the winter-spring season in study 1. But in Study 2, forage Ca c oncentrations were lower than the minimum required levels for all months from the oats plus ryegrass pastures and for early winter months and late spring months from the ryeg rass only pastures. Forage Na concentrations were uniformly low throughout the grazi ng periods of both studies. Magnesium

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83 concentrations were deficient in forages of both forage types in Study 2. Forage CP and IVOMD contents were adequate for grazing b eef cattle throughout th e grazing season in both studies. Summary Two experimental winter-spring grazing studies, each lasting two years were conducted at the North Florida Research a nd Education Center (NFREC), Marianna, Florida to evaluate the organic constituents and macromineral concentrations of annual cool season pasture forages grazed by growi ng beef cattle. Eight 1.32 ha fenced pastures or paddocks were divided into two pastur e land preparation/planting methods, four pastures for the sod seeding treatments and four for the prepared seedbed treatments. These pastures were planted with two different forage combinations small grains, rye/oats mix with or without ryegrass fo r the first two years (Study 1), and oats with ryegrass or ryegrass only for the last two years (Study 2) . Each of the four fo rage/land preparation combination treatments was assigned to tw o pastures each year , thereby giving two replicates per pasture per year. Forage sample s were collected at th e start of grazing and every two weeks thereafter unt il the end of grazing season for each year, pooled by month, and were analyzed for Ca, P, Na , K, Mg, DM yield, CP and IVOMD. Blood plasma samples were also collected from the tester cattle during the spring season of year 2 of Study 2 and were analyzed for Ca, P, and Mg. Month differences were observed in fora ge concentrations of P and K (P<0.0001), and Mg (P<0.05) in both studies, Ca (P<0.01) in Study 1 only, and Na (P<0.05) only in Study 2. Year affected P, K, and Mg con centrations in Study 1 and Ca, P, and Na concentrations in Study 2. In study 2, forage type by month interactions on Ca, K, and Mg concentrations were noticed (P<0.01). Forage Ca was lower than the critical level for

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84 all months from the oat plus ryegrass pastur es, and for early winter months and late spring months from ryegrass only pasture; this difference was significant (P<0.05). Forage concentrations of Na were consis tently low throughout the grazing season and unaffected by forage type or land cultivati on methods used in both studies. Low Mg concentrations of both forage types in St udy 2 (also with high K concentration noted) were indicative of a potential risk of grass tetany or hypomagnesemia for grazing ruminants. Forage DM yields were hi ghly variable with fluctuat ions among the experimental months and found to be higher in spring mont hs, and decreasing toward the end of the grazing season in both studies (P<0.0001). Bo th CP and IVOMD concentrations were greater than the required levels and d ecreased gradually by month in both studies (P<0.0001). Normal plasma concentrations of Ca and P obtained were indicative of a good overall status of these minerals in the animalÂ’s body. Plasma Mg concentrations were slightly above critical level for cattle from both forage types. In summary, the macrominerals most likely to be deficient in North Florida during the cool season would be Ca, Na, and Mg. Special attention should be given to supplementation of Mg since forages reflected a deficiency of this mine ral in the presence of high K concentrations. Implications The use of cool season pasture forages for grazing of growing an imals is of great importance to beef cattle producers, since these forages provide the essential nutrients required for health, maintenance and growth. When the mineral requirements of beef cattle are not met by these forages, appropr iate supplementation with concentrated sources of one or more mineral elements or the use of commercial mineral mixtures may be warranted to make up the concentrations of deficient minerals in the forages. Soil

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85 enrichment with appropriate fertilizer tr eatment should be included to improve the mineral composition of forages.

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86Table 4-1. Forage macromineral co ncentrations in Studies 1 and 2a; level of significanceb Effect Study Ca P Na K Mg Year 1 0.7517 0.0062** 0.8215 0.028* 0.0185* 2 0.0493* 0.0041** 0.0045** 0.0774 0.0896 LPc 1 0.4466 0.1155 0.961 0.5052 0.1081 2 0.1186 0.2146 0.101 0.1158 0.1614 Ford 1 0.4888 0.3773 0.3519 0.6617 0.4662 2 0.0335* 0.9379 0.7147 0.3664 0.1061 LP*For 1 0.4981 0.8997 0.9571 0.1622 0.0717 2 0.1454 0.4424 0.0831 0.1656 0.5020 Month 1 0.0032** <0.0001*** 0.0974 <0.0001*** 0.0488* 2 0.1042 <0.0001*** 0.0406* <0.0001*** 0.0059** For*month 1 -e 2 0.0024** 0.6029 0.8096 0.0013** 0.0012** a Study 1: year 2001-2002 and 2002-2003 and Study 2: year 2003-2004 and 2004-2005. Winter-spri ng grazing season from November to June. b Level of significance: (*) P<0.05, (**) P<0.01, (***) P<0.0001. c LP: pasture land preparatio n/planting method (sod-seeded vs. prepared seedbed) d For: pasture forage type (rye/oats or rye/oats/ryegrass for Study 1 and oa ts/ryegrass or ryegrass only for Study 2. e For*month: not significant (P>0.05) for Study 1.

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87Table 4-2. Forage macromineral concentrations (%, DM) during wi nter-spring grazing season; Study 1a Ca P Na K Mg Month Meanb SEMc Mean SEM Mean SEM Mean SEM Mean SEM Nov 0.37 0.03 0.43 0.03 0.04 0.007 3.8 0.31 0.31 0.03 Dec 0.37 0.02 0.43 0.01 0.03 0.003 4.2 0.16 0.29 0.02 Jan 0.33 0.02 0.47 0.02 0.03 0.005 3.8 0.22 0.28 0.02 Feb 0.31 0.01 0.44 0.01 0.03 0.002 3.3 0.12 0.25 0.01 Mar 0.30 0.01 0.43 0.01 0.03 0.002 3.3 0.12 0.24 0.01 Apr 0.33 0.01 0.38 0.01 0.04 0.002 3.1 0.12 0.27 0.01 May 0.31 0.02 0.32 0.02 0.04 0.004 2.3 0.19 0.27 0.02 a Study 1 (2001-2002 and 2002-2003): year highly si gnificant for P (P<0.01) and significant for K and Mg (P<0.05) and not significant(NS; (P>0.05) for Ca and Na. Pastur e land preparation/planting method (LP) and pasture forage type (For): NS (P>0.05 ) for all the minerals. LP*For: NS (P>0.05) for a ll. Month: significant for Ca (P<0.01) an d Mg (P<0.05) and highly significant for P and K (P<0.0001) and NS (P>0.05) for Na. b Mean = least square mean. c SEM = standard error of mean; n= 2, 8, 4, 16, 16, 16, and 6 for Nov, Dec, Jan, Feb, Mar, Apr, and May, respectively.

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88Table 4-3. Forage macromineral (C a, P) concentrations (%, DM) duri ng winter-spring gr azing season; Study 2a Ca P Month For 1b SEMd For 2c SEM For 1 SEM For 2 SEM Nov 0.28 0.05 0.21 0.05 0.47 0.03 0.45 0.03 Dec 0.23 0.05 0.29 0.05 0.45 0.03 0.44 0.03 Jan 0.25 0.04 0.27 0.04 0.31 0.02 0.33 0.02 Feb 0.17 0.04 0.35 0.04 0.34 0.02 0.33 0.02 Mar 0.22 0.03 0.39 0.03 0.32 0.01 0.35 0.01 Apr 0.28 0.03 0.37 0.03 0.35 0.01 0.36 0.01 May 0.30 0.03 0.30 0.03 0.37 0.01 0.35 0.01 Jun 0.25 0.04 0.26 0.04 0.33 0.02 0.33 0.02 a Study 2 (2003-2004 and 2004-2005): year significant for Ca(P<0.05) and P ( P<0.01). Treatment values: least squares means. Pasture Forage type (For): si gnificant for Ca (P<0.05) and NS for P (P>0.05). Pasture land preparation/planting method (LP): (N S) for Ca and P (P>0.05). LP*For: NS for Ca and P (P>0.05). Month: not significant (NS) for Ca (P>0.05) and highly significant for P (P<0.0001). For*month: significant for Ca (P<0.01) and NS for P (P>0.05). b Pasture forage type 1 (For 1): oats/ryegrass. c Pasture forage type 2 (For 2): ryegrass. d SEM: standard error of mean; n= 4, 4, 8, 8, 16, 16, 16, and 8 for Nov, Dec, Jan, Fe b, Mar, Apr, May, and June, respectively.

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89Table 4-4. Forage macromineral (Na, K, Mg) concentrations (%, DM) duri ng winter-spring grazing season; Study 2a Na K Mg Month For 1b SEMd For 2c SEM For 1 SEM For 2 SEM For 1 SEM For 2 SEM Nov 0.03 0.005 0.04 0.005 3.7 0.20 3.9 0.20 0.17 0.02 0.18 0.02 Dec 0.04 0.005 0.04 0.005 4.5 0.20 4.0 0.20 0.15 0.02 0.18 0.02 Jan 0.04 0.004 0.04 0.004 3.3 0.14 3.1 0.14 0.14 0.01 0.15 0.01 Feb 0.04 0.004 0.05 0.004 3.3 0.14 2.7 0.14 0.13 0.01 0.15 0.01 Mar 0.04 0.003 0.04 0.003 2.8 0.10 3.1 0.10 0.13 0.01 0.19 0.01 Apr 0.04 0.003 0.04 0.003 2.4 0.10 2.9 0.10 0.16 0.01 0.18 0.01 May 0.04 0.003 0.04 0.003 2.3 0.10 2.2 0.10 0.16 0.01 0.16 0.01 Jun 0.03 0.004 0.03 0.004 1.8 0.14 1.7 0.14 0.16 0.01 0.15 0.01 a Study 2 (2003-2004 and 2004-2005): year signif icant for Na (P<0.05) and not signif icant (NS) for K & Mg (P>0.05). Treatment values: Least squares means. Past ure Forage type (For): NS for all the mi nerals (P>0.05). Past ure land preparation/pl anting method (LP): NS for all (P>0.05). LP*For: NS for all (P>0.05). M onth: significant for Na (P< 0.05) and highly significant for K (P<0.0001) & Mg (P<0.01). For*month: NS for Na (P>0.05) and highl y significant for K & Mg (P<0.01). b Pasture forage type 1 (For 1): oats/ryegrass. c Pasture forage type 2 (For 2): ryegrass. d SEM: standard error of mean; n= 4, 4, 8, 8, 16, 16, 16, and 8 for Nov, Dec, Jan, Fe b, Mar, Apr, May, and June, respectively.

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90Table 4-5. Forage dry matter (DM), in vi tro organic matter digestibility (IVOMD), a nd crude protein (CP) in Studies 1 and 2a; level of significanceb Effect Study DM IVOMD CP Year 1 0.3817 <0.0001*** 0.1839 2 0.7963 0.6445 0.0043** LPc 1 0.9147 0.0022** 0.0227* 2 0.9790 0.0431* 0.0520 Ford 1 0.9120 0.6418 0.2507 2 0.4901 0.0330* 0.5415 LP*For 1 0.1876 0.4183 0.7289 2 0.2044 0.7697 0.6271 Month 1 <0.0001*** <0.0001*** <0.0001*** 2 <0.0001*** <0.0001*** <0.0001*** For*month 1 -e 2 0.0147* 0.1679 0.0165* a Study 1: year 2001-2002 and 2002-2003 and Study 2: year 2003-2004 and 2004-2005. Wint er-spring grazing season from November to May. b Level of significance: (*) P<0.05, (**) P<0.01, (***) P<0.0001. c LP: pasture land preparatio n/planting method (sod-seeded vs prepared seedbed). d For: pasture forage type (rye/oats or rye/oats/ryegrass for Study 1 and oats /ryegrass or ryegrass only for Study 2). e For*month: no significant effects for Study 1.

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91Table 4-6. Forage dry matter (DM) yield (kg/ha), in vitro organic matter digestibility (IVOMD; %, DM) and crude protein (CP; %, DM) during winter-spring grazing season; Study 1a DM IVOMD CP Month Meanb SEMc Mean SEM Mean SEM Nov 757 283 83 2 34 2 Dec 1017 144 81 1 30 1 Jan 738 144 84 1 30 1 Feb 818 99 86 1 26 1 Mar 1390 99 81 1 25 1 Apr 1170 99 77 1 22 1 May 492 165 66 1 17 1 a Study 1 (2001-2002 and 2002-2003): year highly significant for IVOMD (P<0.0001) and not significant (NS) for DM and CP (P>0.05). Pasture land preparati on/planting method (LP); significant for IVOMD (P <0.01) and CP (P<0.05), and NS for DM (P>0.05) . Pasture forage type (For) and LP *For: NS for all three (P>0.05). Month: highly significant fo r DM, IVOMD and CP (P<0.0001). b Mean = least square mean. c SEM = standard error of mean; n= 2, 8, 8, 16, 16, 16, and 6 for Nov, Dec, Jan, Feb, Mar, Apr, and May, respectively.

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92Table 4-7. Forage dry matter (DM) yield (kg/ha), in vitro organic matter digestibility (IVOMD; %, DM) and crude protein (CP; %, DM) during winter-spring grazing season; Study 2a DM IVOMD CP Month For 1b SEMd For 2c SEM For 1 SEM For 2 SEM For 1 SEM For 2 SEM Nov 474 156 375 157 87 2 87 2 33 2 31 2 Dec 578 111 594 157 85 2 86 2 27 2 26 2 Jan 328 91 343 91 87 1 88 1 24 1 20 1 Feb 533 91 445 91 85 1 88 1 23 1 23 1 Mar 1207 79 805 79 81 1 84 1 20 1 22 1 Apr 1017 79 1082 79 76 1 80 1 15 1 16 1 May 640 79 791 79 68 1 69 1 13 1 12 1 a Study 2 (2003-2004 and 2004-2005): year highly significant for CP (P<0.01) and not signi ficant (NS) for DM and IVOMD (P>0.05). Treatment values: least squares means; Pasture forage type (Fo r): significant for IVOMD (P<0.05) and NS for DM and CP (P>0.05). Pasture land preparation/planting method (L P): significant for IVOMD (P< 0.05) and NS for DM and CP (P>0.05). LP*For: NS for all (P>0.05). For*Month: highly significant for DM and CP (P<0.01) and NS for IVOMD (P>0.05). Month: highly significant for DM, IVOMD and CP (P<0.0001). b Pasture forage type 1 (For 1): oats/ryegrass. c Pasture forage type 2 (For 2): ryegrass. d SEM= standard error of mean ; n= 4, 4, 10, 12, 16, 16, and 16 for IVOMD and CP and n= 4, 6, 12, 12, 16, 16, and 16 for DM for Nov, Dec, Jan, Feb, Mar, Apr, and May, respectively.

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93 Table 4-8. Plasma macromineral concentra tions in beef cattle during winter-spring grazing season of the second year of Study 2a; level of significance Effect Ca P Mg LPb 0.0775 0.6271 0.3389 Forc 0.931 0.7234 0.1429 LP*For 0.515 0.5759 0.9454 a Samples collected; March of 2005. LP, For, a nd LP*For: not significant (NS) for all the above macrominerals (P>0.05). b LP: Pasture land preparation/ planting method (sod-seeded vs . prepared seedbed). c For: pasture forage type (oats/ ryegrass or ryegra ss); NS (P>0.05). Table 4-9. Plasma macromineral concentratio ns (ppm) in beef cattle during winter-spring grazing season of the second year of Study 2a Ca P Mg Treatment Meanb SEMc MeanSEMMeanSEM For 1d 104 1.36 67 2.52 21 0.42 For 2e 104 1.36 68 2.52 22 0.42 a Samples collected; March of 2005. LP, For and LP*For: not significan t for all the above macrominerals (P>0.05). b Mean: least square mean. c SEM: standard error of means; n= 16. d Pasture forage type 1 (F or 1): oats/ryegrass. c Pasture forage type 2 (For 2): ryegrass.

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94 CHAPTER 5 MINERAL CONCENTRATIONS OF COOL SEASON PASTURE FORAGES IN NORTH FLORIDA DURING WIN TER-SPRING GRAZING SEASON: II. TRACE MINERALS. Introduction Pasture forages are expected to satisfy a major part of the animalÂ’s nutrient requirement for energy, protein, vitamins and minerals. Concen trations of minerals in forages are dependant on at least four ba sic, interdependent factors: (1) genetic differences depending on genus, sp ecies, or strain of plant; (2) the type of soil on which the plant is growing; (3) th e climatic or seasonal conditi ons during growth; and (4) the stage of maturity of the plant (Conrad, 1978). Trace or microminerals are extremely important nutrients functioning as activators of enzyme systems or as components of organic compounds. Changes in trace mineral co ncentrations of fora ges related to season and stage of growth are of greater sign ificance to grazing animals in areas where marginal levels are present (McDowell, 2003). The NRC (2000) has illustrate d the potential improvement of animal health with dietary fortification of trace minerals. Trace elements shown to be required in the diet, especially those for which the metabolic and dietary requirements have been established, tend to concentrate in certain tissues in di rect proportion to the amount supplied in the diet. The concentrations of iron and mol ybdenum in the feed materials should be carefully and periodically monitored because of their antagonistic behavior in the rumen. These two minerals and sulfur can also negatively affect coppe r utilization (Underwood and Suttle, 1999). A program of study was desi gned to compare tilled and sod-seeded

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95 pastures with two combinations of cool seas on annual forages in regards to forage yield and quality, and weight gain and total grazing days by graz ing growing beef cattle over the winter-spring grazing season. The objective of this part of the overall study was to de termine macroand tracemineral concentrations of cool season pasture forages of two combinations of rye, oats and/or ryegrass from tilled or sod-seeded pastures under grazing conditions over four consecutive winter-spring grazi ng seasons (2001-2005) in Nort h Florida. Pasture forage concentrations of the macrominerals and or ganic constituents were reported in the previous chapter (Chapter 4); the present paper evaluates conc entrations of forage trace minerals. Materials and Methods Two experimental cool season grazing studi es were conducted at the North Florida Research and Education Center (NFREC) of the University of Florida located at Marianna in northwest Florida. These studies , each lasting two years, were carried out over four consecutive years from 2001 to 2005 during the winter-spring months, November through May. Both studies were of a 2 x 2 factorial experiment to evaluate two different pasture forage t ypes: small grains (rye and oats mix) with, or without ryegrass for the first two years (Study 1); a nd oats with ryegrass or ryegrass only for the last two years (Study 2). These winter annuals were planted by two land preparation/planting methods, tilled or prepar ed seedbed (PS) and sod-seeded (SS). For each year within each study, eight 1.32 ha fenced pastures or paddocks were utilized for grazing by growing beef cattle. Th e pastures were divide d into two groups of four pastures for the sod seeding treatm ents; and four for the prepared seedbed treatments. Each of the four forage and cu ltivation combination treatments was assigned

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96 to two pastures each year, thereby giving tw o replicates per pastur e treatment per year. The four pastures of the PS treatments were prepared by deep plowing followed by disc harrowing, and the annual pasture forages were planted using a grain drill. In the four pastures assigned for SS treatments, a no-till s eed drill was used and the pasture forage treatments were planted into dormant bahiagrass (Paspalum notatum). The experimental procedures, assignment of animals to experime ntal pastures, grazing patterns and forage sample collection have already been described in chapter 4. For analyses of micromineral concen trations, the samples were ashed and solublized in nitric acid (HNO3) (final acid concentration approximately 5%) using the method described by Miles et al. (2001). Concen trations of forage microminerals, copper (Cu), iron (Fe), zinc (Zn) and manganese (M n) were determined by atomic absorption spectrophotometry (AAS) on a Perkin-Elmer AAS 5000 (Perkin-Elmer, 1980). To ensure the quality of data, the calibration standa rds were prepared simultaneously and the standard curves were recalibrated in the mi ddle and at the end of each set of samples analyzed. In addition, to insure the overall re liability of the analyti cal methods, a certified National Bureau of Standards (NBS) refere nce material (citrus leaves SRM-1572) was acquired from the National Institute of Sta ndards and Technology (NIST, 1998) included as an internal standard with all samples an alyzed. Forage selenium (Se) concentration was determined using the fluorometric method described by Whetter and Ullrey (1978). Forage samples for analyses of cobalt (Co) and molybdenum (Mo) were sent to a private laboratory (PPB Environmental Laboratories, Inc., Gainesville, FL). This laboratory utilized the Inductively Coupled Argon Plasma (ICAP) procedure.

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97 In year two of Study 2 ( 2004-2005) of winter-spring gr azing season, blood samples were obtained from all 32 tester cattle on 03/31/2005 just before the breeding season of the heifers. Blood samples were collected by jugular venupuncture into sodiumheparinized vacutainer tubes and centrifuge d at 700 x g for approximately 20 min at the collection site. Plasma samples were frozen at -20 û C until analyses. Frozen plasma samples were thawed to room temperatur e and deproteinated using 1% lanthanum chloride (LaCl3) and 10% trichloroacetic acid (TCA) as described by Miles et al. (2001). Plasma concentrations of Cu, Fe, Zn and Se were determined by the same procedures as for forages. Liver biopsy samples were obtained unde r aseptic conditions using a collection procedure described by Chapman et al. (1963). About 1-2 g we t liver tissue was collected from each of 32 tester animals. The bl ood on the sample was removed by placing the sample on a filter paper; the sample was then transferred to a whirl-pak plastic bag for storage in an insulated container filled w ith crushed ice, transported to the Animal Nutrition Laboratory, and subsequently frozen until ready to prepare for analyses. Upon thawing, liver samples were dried, wei ghed, and ashed, and solublized in HNO3 (Miles et al., 2001). Liver Cu, Fe, and Mn were analyzed by the same procedures as described above. To ensure the overall reliability of the analytical methods, certified NBS Bovine liver standard (SRM-1577b of NIST; 1998) was r outinely included in the test procedure. Only 12 liver tissues samples selected random ly were analyzed for Se concentration by the fluorometric method previously desc ribed. The data of liver Co and Mo concentrations were obtained from PPB E nvironmental Laboratories for the same 12 samples as those for liver Se.

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98 The experimental design was a complete ly randomized block (2x2) design. The forage microminerals data were analyzed by SAS version 9.0 (SAS Inst, Inc. Cary, NC) PROC MIXED using a repeated measures model, where month was the repeated measure. The procedure estimated the vari ance and covariance of random effects and performed a test of hypothesis on the fixed effects of month, treatment, and month by treatment interactions for both Studies 1 and 2. For plasma and liver mineral data, the SAS procedure performed the tests of fixed e ffects on treatments only (pasture treatment) as month was not involved. Results and Discussion The cattle performance was good during the tw o studies with gain in body weight averaging between 0.8 and 1.15 kg.head-1.day-1 for the various fora ge type-pasture land cultivation/planting method combinations. An imal performance results will be published elsewhere. Forage trace minerals Study 1 Tables 5-1, 5-2, and 5-3 present the level of significance of various effects and mean forage trace mineral c oncentrations during winter-s pring grazing season for Study 1 (2001-2002 and 2002-2003). Year ha d a significant effect on forage Cu (P<0.0001), Fe (P<0.01), and Zn (P<0.05) concentrations and no effect on Mn, Co, Mo, and Se concentrations (P>0.05). Forage concentra tions of Cu, Zn, Mo (P<0.01), and Mn (P<0.05) were affected by pastureland prep aration/planting method (sod-seeding vs. clear tilled or prepared seedbed). Either pasture fo rage type or pasture land preparation method by forage type interaction di d not have any effect on th e trace minerals. Significant

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99 difference in forage concentrations of Cu (P<0.01), Fe, and Zn (P<0.0001) were observed due to month during the grazing seasons. Overall, forage samples had Cu mean c oncentrations in a ll the winter-spring grazing months below the critical level of 10 ppm for beef cattle grazing pastures (McDowell, 2003). Forage Cu concentrations started low in Nove mber and increased gradually in December and January (P<0.01) and declined slightly in February through April and ended low again in May (Table 5-2) . Merkel et al. (1990) reported low values of Cu (3.4 ppm to 5.2 ppm) in forages from th e North Central Florida. Concentrations of Cu are comparatively lower in temperate gr asses (4-7 ppm DM) than legumes (7-8 ppm DM) of the same region (Minson, 1990). Mean forage Fe concentrations were highest during the first three months of winter, November through January, decreased suddenly in February and even more in March, and then increased gradually during late spring months, April and May (P<0.0001). Mean forage Fe concentrations were highly vari able during the winter grazing months and higher initially in the first th ree months than the recommen ded critical level of 100 ppm for grazing beef cattle (NRC, 2000; Mc Dowell, 2003). The reason for the low concentration of forage Fe in March is unknown. Higher Fe concentrations may be due to the acidic pH in soil that favors incr eased availability and plant uptake of Fe (McDowell, 2003). Iron deficiency is unlikely because generally forages contain more Fe than is necessary to meet the requirement of grazing beef cattle (Underwood and Suttle, 1999). Mean forage Zn concentrations were found to be lower in early winter months than the suggested requirement of 40 ppm DM for grazing beef cattle (McDowell, 2003).

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100 Forage Zn started increasing gr adually from November to Ja nuary, decreased slightly in the months of February and March, and agai n increased in the la te spring months (P<0.0001). Minson (1981) reported that most forages are marginal to low in Zn concentration and temperate forages are lower in mean Zn contents than the tropical ones. Forage samples had high Mn concentra tions for all the winter-spring grazing months and mean Mn values were above th e critical level of 40 ppm DM (McDowell, 2003). Berger (1995) and MacPherson (2005) indicated that grasses tend to be considerably higher in Mn than legumes a nd forage Mn is generally well above the concentration suggested for the dietary requi rement of beef cattl e. Cox (1973) reported that forages growing on acid soil have hi gher Mn concentrations and soil acidity markedly increases Mn uptake by forage plants. Forage Co concentrations were variable and below the suggested minimum level of 0.1 ppm DM for grazing beef cattle (McDowe ll, 2003). Cereal forages and grasses are poor sources of Co with con centrations usually within the range of 0.01-0.06 ppm (Field et al., 1988; Singh and Aruna, 1994; Greene et al., 1998). Mi lls (1981) suggested that increasing soil pH from 5.4 to 6.4 reduces the Co content of ryegrass from 0.35 to 0.12 ppm. Mean forage Mo concentrations were f ound to be fluctuating among the months of winter-spring grazing season with high concentr ations only in March. Grasses and cereal forages rarely contain more than 1 ppm Mo DM with a marked variation in Mo levels (0.2 to 0.8 ppm) depending on soil conditions and Mo concentration in forages are elevated by increasing soil pH (Berger, 1995; Greene, 2000).

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101 Mean forage Se concentrations were lo wer throughout the entire winter-spring grazing season and ranged from 0.04 to 0.06 ppm (DM basis), which is less than the recommended critical level of 0.1 to 0.2 ppm for beef cat tle (McDowell, 2003). Whelan et al. (1994) reported that past ure and forage concentrations of Se can be below 0.05 ppm DM and may be as low as 0.02 ppm in areas of low Se soils. Grasses generally contain more Se than legumes at all levels of soil and fertilizer Se (Davies and Watkinson, 1966). Grant and Sheppard (1983) suggested that Se concentrations occurri ng naturally in feeds and forages vary widely, depending on the plan t species, the part of the plant sampled, the season of sampling and the Se status of the soil on which they have grown. The concentrations of Cu, Zn, Mn and Mo were comparatively higher in forages grown in prepared seedbed planting method than those grown in sod-seeding method. Study 2 The level of significance of various e ffects and mean forage trace mineral concentrations during winter-spring grazing season for Study 2 (2003-2004 and 20042005) are presented in Tables 5-1, 5-4, and 5-5. Forage trace minerals, Cu, Zn, Mn, Co, Mo, and Se were not affected by y ear except Fe (P<0.01). Pastureland preparation/planting method had significant effects on Mn (P<0.01), Mo and Se (P<0.05) only. Forage Fe, Zn (P<0.01), Cu, and Se (P< 0.01) were affected by pasture forage types grown (oats/ryegrass or ryegrass only). However pastureland preparation method by forage type interactions did not have any e ffects on forage trace mineral concentrations. Month had significant effects on forage Cu (P<0.05), Fe (P<0.01), Zn, and Mn concentrations (P<0.0001). Forage type by month interactions affected forage concentrations of Cu, Mn (P<0.0001), and Zn (P<0.05).

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102 Similar to Study 1, mean forage Cu was be low the critical level (10 ppm) suggested for grazing beef cattle (NRC, 2000; McDowe ll, 2003) for both pasture forage types evaluated. For the oats and ryegrass pastures , forage Cu levels were highest at the beginning of winter season, November, a nd decreased in the following months, December and January, slightly increased in February and declined again in March (P<0.05). Copper content of forage then incr eased again and leveled off for the rest of winter-spring season (Table 5-4). For ryegrass only pastures, forage Cu concentrations, though lower than the minimum level sugge sted, were steady th roughout the winterspring grazing season but declined in May a nd June. The ryegrass only pastures had high Cu concentrations (P<0.05), compared with the oats-ryegrass pastures. This is in agreement with Minson (1990) who stated th at the Cu declined in forages during the growing season. Increasing temperatures a nd advancing maturity may also have contributed to the low levels of forage Cu ( Underwood and Suttle, 1999). Mean forage Fe concentrations were lo wer than the recommended critical value (100 ppm DM) and fluctuated in all the mont hs of winter-spring grazing season. For oatsryegrass pastures, forage Fe concentrati ons were noticeably hi gher in December and June, when compared with other months wh erein the Fe concentrations were rather steady (Table 5-4). But for the ryegrass only pastures, forage Fe concentrations were variable and above the critical levels in most of the months during the winter-spring grazing season. Mean Fe contents started hi ghest in November, decreased in December and again increased in th e months, January through March (P<0.01). The lowest concentrations of forage Fe were observed in April and May. Forage samples showed a higher Fe concentration in the month of June. Underwood and Suttle (1990) indicated

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103 that the variable high values of Fe in forage plants are attributable to soil contamination, which is most likely to occur on soils prone to waterlogging. For the oats-ryegrass pastures, mean forage Zn concentrations started lower than the suggested minimum level (40 ppm DM) at the beginning of the winter season, November to April and increased in May above the critical level and ended highest in June (P<0.01). But from the ryegrass only pa stures, mean Zn concentrations were above the level required in all the months, being highest in November, decreased slightly in December, increased in the following two months, again declined gradually in April through May, and ended very high in June (P <0.0001). Hambidge et al. (1986) reported that pasture fertilization of cereal species with Zn markedly increases the concentration of this element in forages. High concentrations of Mn were found in th e forages from both treatments in all months with the mean Mn concentrations a bove the critical leve l of 40 ppm DM (NRC, 2000; McDowell, 2003). There were no differe nces in concentra tions between two pasture forage types (P>0.05). Cox (1973) repor ted that higher Mn concentrations are found in forages growing on acid soil. Higher Mn levels in plants may also be contributed by poor drainage (Mitchell, 1963). Analyses of Co, Mo and Se were done from forage samples collected during three months of the winter-spring grazing s eason, March through May. Mean forage Co concentrations were below the critical leve l of 0.1 ppm suggested by NRC (2000) in oatsryegrass pastures only. Acid soil pH and waterlogging favor maintaining the high Co concentrations in pasture grasses ( Berger, 1995; MacPherson, 2000). Molybdenum contents in forages of both pasture forage types were low, perhaps due to soil pH

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104 (Greene, 2000). Forage Se concentrations we re lower than the suggested minimum of 0.1 to 0.2 ppm (McDowell, 2003) and mean leve ls ranged from 0.03 to 0.07 ppm from the oats-ryegrass pastures and 0.05 to 0.08 ppm from the ryegrass only pastures. Low and variable Se concentrations in these forage tr eatments may be due to the changes in mean temperatures that can affect Se conten t of forages (Lindberg and Lannek, 1970). Liver trace minerals The level of significance of va rious treatment effects and mean liver concentrations of trace minerals during winter grazing seas on are presented in Tables 5-6 and 5-7. Pasture land preparation/planting method, pa sture forage type a nd land preparation by forage type did not have any effects on liver trace mineral concentrations (P>0.05). Mean liver Cu concentrations were higher than th e critical level reco mmended (25 ppm) for grazing beef cattle under both treatments. Sim ilarly, mean Fe concentrations in liver samples were found to be above the minimum level of 150 ppm. But, mean liver Mn concentrations were below the suggested cr itical level of 6 ppm (McDowell, 2003) for both pasture forage types, showing that animals had deficient levels of Mn in their livers, which may predispose a deficiency disease. Liver Co concentrations of beef animals that grazed both pasture forage types were higher than the level suggested (0.2 ppm DM ) by Cunha et al. (1964). Salih (1984) found high liver Co values of 0.63 ppm for the wet season in central Flor ida. Mean liver Mo concentrations were lower from animals from both forage types against the critical excess level of 4 ppm. Similar low liver Mo con centration of 3.0 ppm dur ing the winter-spring season was reported by Salih (1984) in central Fl orida. Mean Se concentrations in liver were well above the listed critical level of 0.25 ppm (McDowell, 2003) and were almost

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105 the same for animals from both forage types. McDowell et al. (1989) in a Florida study, found liver Se contents of 0.34 ppm in the winter season. Blood plasma trace minerals Tables 5-8 and 5-9 present the level of significance of various effects and mean plasma trace minerals concen trations during winter-spring grazing season. Plasma Fe and Se concentrations were affected by past ureland preparation/planting method (P<0.05). But forage type and land preparation by fo rage type had no effect on plasma trace minerals (P>0.05). Beef animals within either forage type had higher plasma Cu than the critical level of 0.65 ppm (McDowell, 2003) . Plasma Fe was slightly higher in concentration when compared with the critic al level recommended at 1 ppm (McDowell, 2003). Mean Zn concentrations of plasma were well above the minimum level set for plasma (0.8 ppm). Plasma Zn levels respond very rapidly to diet ary Zn (NCMN, 1973). Mean plasma Se concentrations from both forage types were found to be within the normal range of 0.03 to 0.1 ppm (McDowell, 2003) and were indicative of a good overall status of Se in grazing beef cattle. Ullrey (1987) suggested th at plasma Se concentrations are well correlated with and re flected by dietary Se supply. Pasture forages were deficient in Cu and Se concentrations in both studies. Forage Cu, Zn, Mo and Mn concentrations in Study 1 and Mn, Mo and Se concentrations in Study 2 were significantly affected by pa sture land preparation/planting methods (prepared seedbed). Pasture fora ge type (ryegrass) had an eff ect in concentrations of Cu, Fe, Zn and Se in Study 2 only. Liver and pl asma trace mineral concentrations were normal except slightly low Mn and Mo. S upplementation of Cu and Se would be warranted to maintain beef cattle performance and productivity.

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106 Summary Trace mineral concentrations of annual cool season pasture forages grazed by growing beef cattle during winter-spring grazing season were evaluated during two experimental cool season grazing studies, ea ch lasting two years at the North Florida Research and Education Center (NFREC), Marianna, Florida. Eight 1.32 ha fenced pastures or paddocks were di vided into two groups of past ure land preparation/planting methodsfour pastures for the sod seeding treatments (SS) and four for the prepared seedbed treatments (PS). Two different pastur e forages-small grains, (rye/oats mix) with or without ryegrass for the first two years (St udy 1); and oats with ryegrass or ryegrass only for the last two years (St udy 2) were planted in these pa sture lands. Each of the fourforage type and cultivation combination treat ments was assigned to two pastures each year, thereby giving two replicates per pastur e treatment per year. Forage samples were collected at the start of pasture grazing a nd every two weeks thereafter until the end of grazing season, pooled by month and analyzed for Cu, Fe, Zn, Mn, Co, Mo, and Se. Liver biopsies and blood plasma samples were collected from the tester cattle only at the spring of year two of Study 2 and were analyzed for Cu, Fe, Mn, Zn, Co, Mo, and Se. Forage trace mineral concen trations were found to differ by month in Cu (P<0.01), Fe, and Zn (P<0.0001) in both studies and w ith Mn (P<0.0001) in Study 2 only. Pasture forage type effects on Cu (P <0.05), Fe and Zn (P<0.01) and Se (P<0.05) and forage type by month interactions on Cu and Mn (P< 0.0001) and Zn (P<0.05) were observed in Study 2. Forage concentrations of Cu, Zn, Mn, and Mo in study 1 and Mn, Mo, and Se in Study 2 were affected by pasture land prepara tion/planting methods in that these minerals were found to be lower from forages of sod-seeded treatments than from those of prepared seedbed treatments. Forage Cu c oncentrations were lower than the minimum

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107 requirements among months in both studies. Oats-ryegrass pastures of Study 2 had surprisingly low Fe concentrations in all months of the winter-spring grazing season. Results indicated that Co, Mn, Mo, and Se di d not vary much month to month during the winter-spring grazing months. All mean fo rage Se values were lower than the requirements for grazing beef cattle. There were no differences (P>0.05) in mean Se values between the two studies . Liver Cu, Fe, Co, and Se concentrations were adequate and high enough to indicate adequate status of th ese minerals in tester animals from both forage types. But, liver concentrations of Mn and Mo were slightly low, in relation to beef cattle requirements. Plasma concentrations of Cu, Fe, Se and Zn were all above the required values suggested for beef cattle. In conclusion, the trace mi nerals deficient in North Florida during the cool s eason are Cu and Se, and a speci al consideration should be given to include adequate amounts while s upplementing the mineral mixtures to the growing beef cattle, since forage samples reflected deficient concentrations of these minerals. Implications Feeding the growing beef cattle with cool season annual forages during the winterspring grazing season is of utmost importanc e to beef cattle. A thorough knowledge of essential nutrients available in feeds of a particular area is necessary in designing feeding programs for beef animals. During the wint er-spring grazing seas on, supplementation of trace minerals is of importance for increasing beef cattle productivity.

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108Table 5-1. Forage trace mineral concentrations in studies 1 and 2a; level of significanceb Effect Study Cu Fe Zn Mn Co Mo Se Year 1 <0.0001*** 0.0009** 0.0287* 0.2130 0.9731 0.3348 0.1843 2 0.2380 0.0084** 0.4185 0.5900 0.8394 0.1844 0.4700 LPc 1 0.0092** 0.1494 0.0022** 0.0467* 0.6626 0.0003** 0.3331 2 0.8671 0.9925 0.1138 0.0072** 0.2613 0.0126* 0.0212* Ford 1 0.1133 0.9778 0.1040 0.5278 0.9965 0.2418 0.5889 2 0.0455* 0.0013** 0.0055** 0.4044 0.1859 0.9172 0.0389* LP*For 1 0.9711 0.1881 0.3792 0.7218 0.6736 0.4263 0.5785 2 0.8058 0.3662 0.9346 0.3699 0.3425 0.7990 1.0000 Month 1 0.0003** <0.0001*** <0.0001*** 0.0820 2 0.0353* 0.0020** <0.0001*** <0.0001*** For*month 1 -e 2 <0.0001*** 0.1877 0.0299* <0.0001*** a Study 1; year 2001-2002 and 2002-2003 and Study 2: year 2003-2004 and 2004-2005. Winter-spr ing grazing season from November to June b Level of significance: (*) P<0.05, (**) P<0.01, (***) P<0.0001. c LP: pasture land preparation/ planting methods (sod-seeded or prepared seedbed). d For: pasture forage type (rye/oats or rye/oats/ryegrass for Study 1, and oats /ryegrass or ryegrass only for Study 2). e For*month: no significant effects for study 1.

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109Table 5-2. Forage trace mineral (Cu, Fe, Zn, Mn) concentrati ons (ppm of DM) during winter -spring grazing season; Study 1a Cu Fe Zn Mn Month Meanb SEMc Mean SEM Mean SEM Mean SEM Nov 5.8 0.71 190 25.3 30 5.4 82 14.9 Dec 7.7 0.36 126 12.8 33 2.9 95 9.1 Jan 8.2 0.51 178 18.0 41 4.0 111 11.4 Feb 6.1 0.24 98 8.4 37 2.2 106 7.6 Mar 6.0 0.24 75 8.4 36 2.2 105 7.6 Apr 6.4 0.24 92 8.4 41 2.2 105 7.6 May 5.5 0.41 105 14.7 60 3.3 125 9.9 a Study 1 (2001-2002 and 2002-2003); year highly significant for Cu (P<0.0001) and significa nt for Fe (P<0.01) and Zn (P<0.05) a nd not significant (NS) for Mn (P>0.05). Past ure land preparation/planting method (LP): significant for Cu and Zn (P<0.01) and Mn (P<0.05) and NS for Fe (P>0.05). Pasture forage type (For): NS for all. LP*For: NS fo r all. Month; highly significant for Fe an d Zn (P<0.0001) and significant for Cu (P<0.01) and NS for Mn (P>0.05). b Mean= least square means. c SEM= standard error of mean; n= 2, 8, 4, 16, 16, 16, and 6 for Nov, Dec, Jan, Feb, Mar, Apr, and May, respectively.

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110Table 5-3. Forage trace mineral (Co, M o, Se) concentrations (ppm of DM) dur ing winter-spring grazing season; Study 1a Co Mo Se Month Meanb SEMc Mean SEM Mean SEM Dec 0.05 0.04 0.43 0.26 0.05 0.02 Feb 0.03 0.02 0.72 0.16 0.05 0.01 Mar 0.02 0.02 1.08 0.13 0.04 0.01 Apr 0.08 0.01 0.78 0.09 0.06 0.01 May 0.09 0.04 0.82 0.26 0.06 0.02 a Study 1 (2001-2002 and 2002-2003); year not signi ficant (NS) for all the three minerals , Co, Mo, and Se (P>0.05). Pasture land preparation/planting method (LP): significant for Mo (P<0.01) and NS for Co and Se (P>0.05). Pastur e forage type (For): NS for all (P>0.05). LP*For: NS for all (P>0.05) . Month; no significant effects. b Mean= least square means. c SEM= standard error of mean; n= 1, 3, 4, 7, and 1 for Dec, Feb, Mar, Apr, and May, respectively.

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111Table 5-4. Forage trace mineral (Cu, Fe, & Zn) concentrations (ppm of DM) during winter-spring grazi ng season; Study 2a Cu Fe Zn Month For 1b SEMd For 2c SEM For 1 SEM For 2 SEM For 1 SEM For 2 SEM Nov 5.0 0.67 6.4 0.67 63 17.1 107 17.1 31 6.5 51 6.5 Dec 3.9 0.67 5.9 0.67 81 17.1 85 17.1 34 6.5 44 6.5 Jan 3.9 0.53 6.1 0.53 58 12.2 108 12.2 31 4.7 52 4.7 Feb 4.8 0.53 5.3 0.53 67 11.6 114 11.6 39 4.6 56 4.6 Mar 3.9 0.44 7.1 0.44 62 8.3 102 8.3 31 3.4 48 3.4 Apr 4.7 0.44 5.9 0.44 56 8.3 71 8.3 38 3.4 46 3.4 May 4.9 0.44 4.7 0.44 57 8.3 63 8.3 46 3.4 47 3.4 Jun 4.8 0.53 4.3 0.53 89 11.9 115 11.9 82 4.7 80 4.7 a Study 2 (2003-2004 and 2004-2005): yearhighly si gnificant for Cu, Fe and Zn. Treatment values: least squares means. Pasture forage type (For): significant for Cu (P<0.05) and highly signi ficant for Fe and Zn (P<0.01). Pa sture land preparation/planting method (LP): not significant (NS) for all the th ree minerals (P>0.05). LP*For: NS for all (P.0.05). For*month: highly significant for Cu (P<0.0001), Zn (P<0.05), and NS for Fe (P>0.05). Month: Significant for Cu (P<0.05), Fe (P<0.01) and highly significant for Zn (P<0.0001). b Pasture forage type 1 (For 1): oats/ryegrass. c Pasture forage type 2 (For 2): ryegrass. d SEM: standard error of mean ; n= 4, 4, 8, 8, 16, 16, 16, and 8 for Nov, Dec, Jan, Feb, Mar, Apr, May, and June, respectively.

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112Table 5-5. Forage trace minera l (Mn, Co, Mo, & Se) concentra tions (ppm of DM) during wint er-spring grazing study; Study 2a Mn Co Mo Se Month For 1b SEMd For 2c SEMFor 1 SEMFor 2 SEM For 1 SEMFor 2 SEMFor 1SEMFor 2 SEM Nov 95 12.9 70 12.9 Dec 134 12.9 80 12.9 Jan 85 9.7 106 9.7 Feb 78 9.6 104 9.6 Mar 80 7.5 137 7.5 0.03 0.03 0.10 0.02 0.70 0.30 0.56 0.23 0.07 0.01 0.07 0.01 Apr 103 7.5 120 7.5 0.04 0.03 0.11 0.05 0.67 0.33 0.98 0.45 0.05 0.01 0.05 0.01 May 123 7.5 124 7.5 0.09 0.05 0.14 0.05 0.35 0.47 0.11 0.45 0.03 0.01 0.08 0.01 Jun 136 9.7 152 9.7 a Study 2 (2003-2004 and 2004-2005): year not signi ficant (NS) for Mn, Co, Mo, and Se. Tr eatment values: least squares means. Pasture forage type (For): sign ificant for Se (P<0.05) and not significant (NS) for the other minerals, Mn, Co, and Mo. Pasture land preparation/planting method (LP): highly signi ficant for Mn (P<0.01) and Mo, Se (P<0.05) and NS for Co (P>0.05). LP*For: NS for all (P>0.05). For*month: highly significant for Mn (P<0.0001) and no effects for Co, Mo, and Se. Month: highly significant for Mn (P<0.0001) and no significant effects for Co, Mo, and Se. b Pasture forage type 1 (For 1): oats/ryegrass. c Pasture forage type 2 (For 2): ryegrass. d SEM= standard error of mean; n= 4, 4, 8, 8, 16, 16, 16, and 8 for Mn for Nov, Dec, Jan, Feb, Mar, Apr, May, and June, respectiv ely and n= 9, 5, and 2 for Co, Mo, and Se for Mar, Apr, and May, respectively.

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113Table 5-6. Liver trace mineral concentrations in beef cattl e during winter-spring grazing season of the second year of Study 2a; level of significance Effect Cu Fe Mn LPb 0.2651 0.4783 0.9728 Forc 0.4555 0.0601 0.9782 LP * For 0.4155 0.7250 0.6388 a Samples collected; March of 2005. LP, For, and LP*For; not significant (P>0.05) for all th e above trace minerals. b LP: pasture land preparatio n/planting method (sod seeded or prepared seedbed). c For: pasture forage type (oats/ryegrass or ryegrass).

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114Table 5-7. Liver trace mineral concentrations (ppm of DM) in beef cattle during winter -spring grazing season of the second yea r of Study 2a Cu Fe Mn Co Mo Se Pasture forage type Meand SEMe Mean SEM Mean SEM Mean SEM Mean SEM Mean SEM For 1b 169 17.7 240 18.4 4.5 0.5 0.36 0.04 3.43 0.32 0.76 0.03 For 2c 190 17.7 164 18.4 4.5 0.5 0.29 0.04 2.73 0.32 0.72 0.03 a Samples collected; March of 2005. Pasture la nd preparation/planting method (sod seeded vs prepared seedbed) and pasture forage type: no significance (P>0.05). LP *For: no significance (P>0.05). b Pasture forage type 1 (F or 1): oats/ryegrass. c Pasture forage type 2 (For 2): ryegrass. d Mean= least square means. e SEM= standard error of mean; n= 16 for Cu, Fe, and Mn and n=6 for Co, Mo, and Se.

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115Table 5-8. Plasma trace mineral concentr ations in beef cattle during winter-spri ng grazing season of the second year of Study 2a; level of significance Effect Cu Fe Zn Se LPb 0.0580 0.0294* 0.8696 0.0318* Forc 0.5818 0.9866 0.5780 0.2054 LP*For 0.4483 0.1565 0.2565 0.2054 a Samples collected; March of 2005. LP: significant for Fe and Se (P<0.05). For, and LP*For: not si gnificant for all the above t race minerals (P>0.05). b LP: pasture land preparation/ planting method (sod-seeded or prepared seedbed). c For: pasture forage types (oats/ryegrass or ryegrass). Table 5-9. Plasma trace mineral concentra tions (ppm) in beef cattle during winter-s pring grazing season of the second year of Study 2a Cu Fe Zn Se Pasture forage type Meanb SEMc Mean SEM Mean SEM Mean SEM For 1d 0.90 0.04 1.06 0.15 1.30 0.07 0.09 0.003 For 2e 0.86 0.04 1.07 0.16 1.24 0.07 0.08 0.003 a Samples collected; March of 2005. Pasture la nd preparation/planting method (LP): signi ficant for Fe and Se only. Pasture forage type (For) and LP*For: not significant for all the above microminerals. b Mean: least square means c SEM: standard erro r of means; n=16. d Pasture forage type 1 (F or 1): oats/ryegrass. e Pasture forage type 2 (For 2): ryegrass. .

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116 CHAPTER 6 SUMMARY AND CONCLUSION Two studies on winter-spri ng grazing seasons, each lasting two years, were conducted at the North Florida Research a nd Education Center (NFREC), Marianna, Florida to evaluate the organic constituents and mineral concentra tions of annual cool season pasture forages grazed by growing beef cattle. Eight 1.32 ha fenced pastures or paddocks were utilized for these studies. Two different forage combinations, small grains, rye/oats mix with or without ryegrass for the first two years (Study 1) and oats with ryegrass or ryegrass only for the last two years (Study 2), were planted in two groups of land preparation/pl anting methods-sod seeding trea tment and prepared seedbed treatment. Each of the four-forage/cu ltivation combination treatments was assigned to two pastures each year, thereby giving two repli cates per pasture per year. Forage samples were collected at the start of grazing of th e pastures and every two weeks thereafter until the end of grazing season for all the four years, and were analyzed for macrominerals (Ca, P, Na, K, and Mg), DM yield, orga nic constituents (CP and IVOMD) and trace minerals (Cu, Fe, Zn, Mn, Co, Mo, and Se). Liver biopsies and blood plasma samples were also collected from the tester cattle only during March of year 2 of Study 2 and were analyzed for both macro and trace minerals for the mineral status in the animal body. Forage macrominerals were found to have month differences in concentrations of Ca (P<0.01), P, and K (P<0.0001), and Mg (P< 0.05) in both studies and Na (P<0.05), and

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117 Ca (P>0.05) in Study 2 only. Year eff ected P (P<0.01), K, and Mg (P<0.05) concentrations in Study 1 and Ca (P<0.05), P, and Na (P<0.01) concentr ations in Study 2. Forage Ca concentrations in Study 2 only show ed difference due to forage type (P<0.05). In Study 2, forage type by month interacti ons on Ca, K, and Mg concentrations were noticed (P<0.01). Forage Ca, P, K, and Mg concentrations were high and adequate for grazing beef cattle throughout the winter -spring season in Study 1. But in Study 2, forage Ca concentrations were slightly lower than the required levels for all months from the oatsryegrass pastures, and for early winter months and late spring mont h from the ryegrass pastures only. Phosphorus and K concentra tions were found to be higher from both forage types of Study 2 (P<0.0001) than th e suggested critical levels. Forage concentrations of Na were consistently lo w throughout the winter -spring grazing season and unaffected by forage type or land cultiv ation/planting methods used in both studies. Low Mg concentrations in forages from bot h forage types in St udy 2 along with high K levels were indicative of a potential risk of grass tetany or hypomagnesemia in grazing ruminants. Forage DM yields were hi ghly variable with fluctuat ions among the experimental months and found to be higher in spring months and decreased toward the end of grazing season in both studies (P<0.0001). Both CP and IVOMD concentra tions were observed above the recommended levels and found declin ing gradually at the end of the grazing seasons in both studies (P<0.0001). Normal pl asma concentrations of Ca and P were indicative of a good overall status of these mi nerals in animalÂ’s body. Plasma Mg levels were slightly high in animals from both fo rage types. In summary, the macrominerals

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118 more likely to be deficient in north Flor ida areas are Ca, Na, and Mg and a special attention should be given to supplementation of Mg, since forage samples reflected a deficiency of this mineral. Month differences in forage trace mineral concentrations were found in Cu, Fe, and Zn in both studies and also Mn in study 2. Pa sture forage type effects on Cu (P<0.05), Fe, Zn (P<0.01) and Se (P<0.05) and forage type by month interactions on Cu, Mn (P<0.0001) and Zn (P<0.05) were observed in Study 2. Forage Cu concentrations were low with variations among months in both st udies. Differences in Cu concentrations between forage types of Study 2 were observed indicating that forage type varied in Cu concentrations. Iron concentrations in forage s were greater at early period to middle of winter grazing season, then decreased below the critical limit, and were higher at the end of spring season in Study 1, and ryegrass onl y of Study 2. Forage Fe was consistently lower in concentrations than the dietary requirements for grazing beef cattle in oatsryegrass forage types of Study 2. Forage Zn concentrations were lower in most of the months during winter-spring season and highest toward the end of winter -spring season in Study 1 and oats-ryegrass pastures of study 2, and were higher than th e critical level for all the winter-spring months in ryegrass only past ure of Study 2. Mean forage Mn contents were generally above the requirements of 40 ppm for both st udies, showing an upward increase among months in Study 1, and ryegrass only of St udy 2 and variable levels in oats-ryegrass pasture of Study 2 (P<0.0001). Forage Co concentrations were all below the critical level in Study 1, and for oatsryegrass of study 2. Forages of ryegrass only had adequate levels of Co in all the

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119 sampling months. Mean forage Mo concentrations were within the normal range of 0.2 to 0.8 ppm for all months in both studies excep t a high value in the month of March in Study 1 and a very low value in the month of May from ryegrass only of Study 2. All mean forage Se values were lower than the requirements and varied among months. There were no differences (P>0.05) in mean Se values between the two studies. Liver Cu, Fe, Co, and Se concentrations were adequate and high enough to meet the requirement, suggesting an overall good stat us of these minerals in tester animals grazing both forage types. However, low c oncentrations of Mn and Mo were found in liver and were indicative of a necessity for extra supplementation of these minerals for growing beef animals. Plasma concentrations of Cu, Fe, Se and Zn were all above the required levels suggested for beef cattle, indi cative of sufficient levels of these minerals in animalÂ’s body.

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144 BIOGRAPHICAL SKETCH Gunasegaran Chelliah was born on September 24, 1963, in Pulau Pinang, Penang, Malaysia. When he was seven years old, his father took him to India for his education. He attended high school and passed higher secondary courses at Ramanathapuram, Tamilnadu State, South India. He ranked fi rst in all his academic years of schooling. After higher secondary school, he was admitte d to the school of Veterinary Medical Sciences at Madras Veterinary College, Ma dras, India. He obtained his Bachelor of Veterinary Science (B.V.Sc) de gree with distinction in 1988. He started his career as a Veterinary A ssistant Surgeon at Sri Ram Veterinary Clinic, Butterworth, Malaysia. In 1990, he join ed Teck Huat Farming Pvt. Ltd (Charoen Pokphand Group of Companies), Ulu Tiram, J ohor State as a farm veterinarian and assistant manager and he was in charge of poultry health and management, biosecurity and biocontainment, broiler-breeder operations . He was then transferred to the poultry processing plant and worked as a quality control veterinarian and technical coordinator for contract broiler farming operations under the same group of companies at Seremban, Negeri Sembilan State. He later joined T hurgas Industries Pvt. Ltd, Bukit Mertajam, Penang in 1995 and was appointed as an executi ve director for human resources, office management, finance, accounts and exports. He was married in 1991, and has now two ch ildren, aged thirteen and nine. After sixteen years of working in different positions , he decided to pursue his higher education in USA. In January of 2004, he was admitted as a graduate student at the Department of

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145 Animal Sciences, University of Florida. Sin ce then, he has been working on his MasterÂ’s degree.