Effects of Feeding Perennial Peanut Hay on Growth, Development, Attainment of Puberty, and Fertility in Beef Replacement...

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Title:
Effects of Feeding Perennial Peanut Hay on Growth, Development, Attainment of Puberty, and Fertility in Beef Replacement Heifers
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1 online resource (98 p.)
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english
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Bischoff,Kalyn M
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University of Florida
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Gainesville, Fla.
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Degree:
Master's ( M.S.)
Degree Grantor:
University of Florida
Degree Disciplines:
Animal Sciences
Committee Chair:
Lamb, Graham
Committee Members:
Dilorenzo, Nicolas
Myer, Robert O
Adesogan, Adegbola T

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Subjects / Keywords:
beef -- bermudagrass -- fertility -- growth -- hefier -- peanut -- perennial -- puberty -- replacement
Animal Sciences -- Dissertations, Academic -- UF
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Animal Sciences thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
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Abstract:
The objective of this study was to determine the influence of supplemental feeding of perennial peanut hay (Arachis glabrata Benth.) on growth performance and age at puberty in growing beef cattle heifers. Over a two year period, 120 heifers were randomly allocated into pens and assigned to one of three supplement treatments: 80% corn and 20% soybean meal supplement (CSBM), perennial peanut hay supplementation (PPH), and a control which received no supplement (CON). All heifers received ad libitum access to bermudagrass hay (Cynodon dactylon (L.) Pers.) during the 140-developmental phase. Following the developmental phase, heifers were comingled for a 77 d breeding season during the breeding phase. Period influenced ADG (P = 0.002) and treatment effected ADG, with the CON tending (P = 0.06) to be have lesser ADG than the CSBM and PPH heifers. There was a treatment ? day interaction (P = 0.06) on mean body weight (BW) with heifers in the CON treatment being lighter at the conclusion of the development phase (P = 0.02). Total DMI during the 140-d development phase was greater (P < 0.01) for PPH (5.3 ? 0.25 kg.hd-1.d-1) than for CON (3.4 ? 0.25 kg.hd-1.d-1), and CSBM heifers (4.3 ? 0.25 kg.hd-1.d-1), with CSBM being greater than CON. There was no effect of treatment on age (P = 0.32), BW (P = 0.16), and body condition score (BCS; P = 0.27) at attainment of puberty, nor days on treatment prior to attainment of puberty. In addition, no differences in fetal age (P = 0.34) and overall pregnancy rate (P = 0.50) were observed. In conclusion, there were no differences among treatments in reproductive performance despite the occurrence of differences in DMI, BW, and ADG, making PPH a viable feed option in the southeastern United States of America for replacement heifer development.
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In the series University of Florida Digital Collections.
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Includes vita.
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Statement of Responsibility:
by Kalyn M Bischoff.
Thesis:
Thesis (M.S.)--University of Florida, 2011.
Local:
Adviser: Lamb, Graham.

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1 EFFECTS OF FEEDING PERENNIAL PEANUT HAY ON GROWTH, DEVELOPMENT, ATTAINMENT OF PUBERTY, AND FERTILITY IN BEEF REPLACEMENT HEIFERS By KALYN MARIE BISCHOFF A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2011

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2 2011 Kalyn Marie Bischoff

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3 To my family

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4 ACKNOWLEDGMENTS Most importantly, I would like to thank my Lord and Sav i or for giving me the strength, wisdom and passion that allow s me to achieve the desires of my heart The opportunities He has allowed me to live out are beyond what I could have dreamed. In addition, I would like to thank my family My parents have been an unwavering source of support, and taught me at a young age that hard work and dedication will take you far in life They are my biggest fans and I know that I will always have a place to call home. Thank you to m y sister, Sammi, who drives me to be better every day and handles lifes challenges with grace, courage, a nd love in every circumstance. In addition I would like to thank my brother in law Pat, who is fighting overseas for our nation s freedom, all the while being an amazing husband and father, and Weston m y first nephew who brings so much joy to our entire family I would also like to thank two of my best friends, Tyler and Clayton, my brothers N o matter what, they have always been there for me, and thank s to my grandmother Leone for her love, support a nd Sunday chats! The friends that have supported me, and made my life the joy that it is too numerous to mention, I have been blessed immensely to have these people sharing my life with me and for that I am eternally grateful My thanks are not enough f or T era Black and Vitor Mercadante. Tera is one of my dearest friends, the hours, miles and laughs we shared are some of my best memories of graduate school Her love of life is intoxicating! Obrigado to Vi tor who was always willing to help with the wo rst job! Be it doing round bales orts at 9 P.M or feeding heifers on cold early morning s, he is a true friend I can always count on. I would also like to thank their other halves Paula and Seth, who are truly great friends, as well as Guilherme Marquezi ni I would also like to thank everyone at the NFREC Tina, Gina,

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5 Mary, David, Olivia, Mark, Pete, Harve y, Don Don, Butch, the farm shop guys, and peanut crew; everyone has been a joy to work with. I truly love coming to work every day and you hav e a bi g part to do with that Dr Cliff Lamb has become not only a mentor but also a great friend in the past two years I am thankful that he believed in me and allowed me to have the opportunity to work with him Not only is he a role model for my career b ut also in life In addition, I would like to Dr Nicolas DiLor enzo, whose door is always open; he is always willing to help. I would also like to thank their families for welcoming me into their lives, never once have I felt 2,000 miles away from home I would also like to thank the United States department of agriculture ( USDA ) for funding this study through a TSTAR C grant and ABS Global, Inc orporated for the donation of the semen each year In addition to Dr Bob Myer and Dr Gbola Adesogan for being excellent committee members, giving guidance and support throughout my masters Lastly, I would like to thank Jason Waters I never dreamt that I would meet the man of my dreams working bulls in Florida, but God has an amazing plan for each of our liv es! He knows and understands me better than anyone, and is my best friend. His willingness to help me achieve my goals and live my dream is something I am truly thankful for

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6 TABLE OF CONTENTS page ACKNOWLEDGMENTS .................................................................................................. 4 LIST OF TABLES ............................................................................................................ 8 LIST OF FIGURES .......................................................................................................... 9 LIST OF ABBREVIATIONS ........................................................................................... 10 ABSTRACT ................................................................................................................... 12 CHAPTER 1 INTRODUCTION .................................................................................................... 14 2 LITERATURE REVIEW .......................................................................................... 17 Attainment of Puberty ............................................................................................. 17 Puberty ............................................................................................................. 17 Hormonal Change ............................................................................................ 17 Hypothalamic GnRH Neurons .......................................................................... 19 Follicle Dynamics ............................................................................................. 20 Factors Affecting Puberty ........................................................................................ 21 Genetics ........................................................................................................... 21 Weight .............................................................................................................. 22 Age ................................................................................................................... 23 Body Composition ............................................................................................ 23 Metabolic Indicators ......................................................................................... 24 Time of Gain ..................................................................................................... 26 Rate of Gain ..................................................................................................... 26 Plane of Nutrition .............................................................................................. 27 Predicting Puberty ............................................................................................ 27 Concepts of Nutrition .............................................................................................. 28 Effect of Nutrition on Reproduction ................................................................... 28 Regulation of Intake ......................................................................................... 29 Energy .............................................................................................................. 31 Protein .............................................................................................................. 33 Nutrient Synchrony ........................................................................................... 34 Associative Effects ........................................................................................... 35 Nitrogen Recycling and Blood UreaNitrogen ................................................... 35

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7 3 EFFECTS OF FEEDING PERENNIAL PEAN UT HAY ON GROWTH, DEVELOPMENT, ATTAINMENT OF PUBERTY, AND FERTILITY IN BEEF REPLACEMENT HEIFERS .................................................................................... 39 Materials and Methods ............................................................................................ 40 Anim als and Treatments ................................................................................... 40 Feed Sample Collection and Analysis .............................................................. 42 Blood Collection and Analyses ......................................................................... 44 Assessment of Puberty ..................................................................................... 45 Temperament Characteristics .......................................................................... 46 Reproductive Management .............................................................................. 46 Statistical Analysis .................................................................................................. 47 Results and Discussion ........................................................................................... 50 Feed Intake ...................................................................................................... 50 Animal Growth and Performance ..................................................................... 52 Fertility .............................................................................................................. 57 Temperament ................................................................................................... 60 Conclusion .............................................................................................................. 62 LIST OF REFERENCES ............................................................................................... 79 BIOGRAPHICAL SKETCH ............................................................................................ 98

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8 LIST OF TABLES Table page 3 1 Nutritional values of feeds offered during the developmental phase. ................. 74 3 2 Ch emical composition of the mineral supplements provided to developing heifers during the development phase and breeding phase. .............................. 75 3 3 Nutritional values of feed available to heifers during the breeding phase. .......... 76 3 4 DMI parameters of heifers during the development phase and growth parameters. ........................................................................................................ 77 3 5 T emperament data (Year 2 only) during the development phase and fertility data. ................................................................................................................... 78

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9 LIST OF FIGURES Figure page 3 1 Schematic representing data collection for the develop ment and breeding phase for heifers receiving different development diets. ..................................... 63 3 2 Schematic of specific breeding events during the breeding phase for heifers receiving different developmental diets. ............................................................. 64 3 3 Mean ADG in kg by period for heifers receiving three different development diets.. .................................................................................................................. 65 3 4 Mean BW by day for heifers receiving three d ifferent developmental diets. ...... 66 3 5 Mean BCS (scale of 1 to 9, with 1 = emaciated and 9 = obese) by day for heifers during the receiving three different developmental diets. ........................ 67 3 6 Mean pen score by day for heifers receiving three different development diets.. .................................................................................................................. 68 3 7 Mean chute score (on 5 point s cale, with 1 being calm and 5 being aggressive) by day for heifers receiving three different development diets.. ..... 69 3 8 Mean exit velocity by day for heifers receiving three different develop ment diets.. .................................................................................................................. 70 3 9 Mean temperature by 28 d period during the development and breeding phase for heifers receiving three different development diets. ............................ 71 3 10 Mean relative humidity by 28 d period during the development and breeding phase for heifers receiving three different development diets. ............................ 72 3 11 Mean rainfall by 28 d period during the development and breeding phase for heifers receiving three different development diets ............................................ 73

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10 LIST OF ABBREVIATION S ACTH Adrenocorticotropic hormone ADF Acid detergent fiber ADG Average daily gain AGR P Agouti related protein AI Artificial Insemination BCS Body condition score on a 1 to 9 scale BGH B ermudagrass hay BUN Blood urea nitrogen BW Body weight CL Corpus luteum CON Control treatment : no supplement CP Crude protein CS Chute score on a 1 to 5 s cale CSBM Corn and soybean meal supplemented treatment CT Condensed tannins D Day DMI Dry matter intake EV Exit velocity FFA Free fatty acid FSH Follicle stimulating hormone GnRH Gonadotropinreleasing hormone HOT Hepatic oxidation theory Hr Hour IGF I Insulin like growth factor I

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11 Im I ntramuscular LH Luteinizing hormone Max Maximum Min Minimum NDF Neutral detergent fiber NPN Nonprotein nitrogen NPY Neuropeptide Y NSC Nonstructural carbohydrate PDV Portal drain viscera PGF2 Prostaglandin PPH Perenni al peanut hay supplemented treatment PS Pen score on a 1 to 5 scale RTS Reproductive tract score SC Structural carbohydrate TDN Total digestible nutrient TRT Treatment VFA Volatile fatty acid Vs. Versus Yr1 Year 1: October 2009 to June 2010 Yr2 Year 2: October 2010 to June 2011

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12 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science EFFECTS OF FEEDING PERENNIAL PEANUT HAY ON GROWTH, DE VELOPMENT, ATTAINMENT OF PUBERTY, AND FERTILITY IN BEEF REPLACEMENT HEIFERS By Kalyn Marie Bischoff August 2011 Chair: G.C Lamb Major: Animal Science The objective of this study was to determine the influence of supplemental feeding of perennial peanut hay ( Arachis glabrata Benth.) on growth performance and age at puberty i n growing beef cattle heifers Over a two year period, 120 heifers were randomly allocated into pens and assigned to one of three supplement treatments: 80 % corn and 20% soybean m eal supplement (CSBM), perennial peanut hay supplementation (PPH), and a control which received no supplement (CON) All heifers received ad libitum access to bermudagrass hay ( Cynodon dactylon (L.) Pers. ) during the 140d evelopmental phase. Following th e developmental phase, heifers were comingled for a 77 d breeding season during the breeding phase P eriod influenced ADG ( P = 0.002) and treatment effected ADG, with the CON tending ( P = 0.06) to be have lesser ADG than the CSBM and PPH heifers T here w as a treatment day interaction ( P = 0.06) on m ean body weight ( BW ) with heifers in the CON treatment being lighter at the conclusion of the development phase ( P = 0.02) Total DMI during the 140d development phase was greater ( P < 0.01) for PPH ( 5.3 0. 25 kg.hd1.d1) than for CON ( 3.4 0.25 kg.hd1.d1), and CSBM heifers ( 4.3 0.25 kg.hd1.d1) with CSBM being greater than CON There was no effect of treatment on age ( P = 0.32 ),

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13 BW ( P = 0.16), and body condition score ( BCS; P = 0.27 ) at attainment of puberty, nor days on treatment prior to attainment of puberty In addition, no differences in fetal age ( P = 0.34) and overall pregnancy rate ( P = 0.50 ) were observed. In conclusion, there were no differences among treatments in reproductive performance despite the occurrence of differences in DMI, BW and ADG, making PPH a viable feed option in the southeastern U nited States of America for replacement heifer development

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14 CHAPTER 1 INTRODUCTION The successful development of replacement heifers to sustain cow numbers in the United States beef industry is critical for meeting the world s growing protein requirement As of January 2011, there were 30.9 million beef cows with 5.2 million replacement heifers on inventory within the U.S. A (USDA, 201 1) With repl acement heifer numbers decreasing by 5% from 2010, the size of the U.S cow herd will likely continue to decline during the next two years, making it essential for proper development of existing heifers to ensure their successful entrance int o the cow herd. In Florida, there are more than 110,000 head of replacement heifers that may be developed to sustain the 926,000 head of beef cows (USDA, 2011) However, producers face regional challenges, making the management of replacement heifer development even more of a challenge. It is est imated that heifers must reach a target weight of approximately 65% of t heir mature body weight (BW) to attain puberty (Patterson et al., 1991) and heifers that become pregnant early in the breeding season will continue to do so as cows (Albaugh and Strong, 1972; Lesmeister et al., 1973) with increased lifetime production rates (Byerl e y et al., 1987) Therefore, ensuring proper nutritional management of heifers allowing adequate average daily gain ( ADG ) to sup port the attainment of puberty is a focus in heifer development While these managem ent goals are widely understood they present a major expense for producers; therefore, management strategies that allow attainment of these goals must be considered in order to meet the needs of the growing female, while minimizing the opportunity cost associated with that heifer becoming pregnant and reaching the production phase of her life (Clark et al., 2005) In

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15 addition, continually rising corn and co mmodity prices make concentratebased supplementation economically challenging resulting in the need for exploration of alternative nutritional methods of heifer development While bermudagrass ( Cynodon dactylon (L.) Pers.) is one of the main forages in the southeast ern U.S.A. its low dry matter ( DM ) digestibly and crude protein ( CP ) concentrations make it nutritionally inadequate as a sole source of feed for growing or lactating beef cattle (Duble et al., 1971; Johnson et al., 2001) Thus a common feeding strateg y is to supplement poor quality basal gras s diets with legume forage which results in increase d DMI and diet digestibility in ruminant livestock (Minson and Milford, 1967; Getachew et al., 1994) With production of perennial peanut forage ( Arachis glabrata Benth.) growing in popularity over the past decade in regions known for bermudagrass production (Myer et al., 2009) its use as a supplement in low quali ty forage based diets could yield favorable results in ruminant production scenarios Perennial pea nut forage is a warm season, tropical legume, native to South A merica, which is comparable to alfalfa ( Medicago sativa L.) in nutritive value and feeding quality (French et al., 2006 ; Myer et al., 2009) In Florida, it is estimated that 12,140 hectares ar e planted annually (Newman et al., 2009) In addition, it is estim ated that every 404 hectares of coastal bermudagrass that is replaced with perennial peanut production will y ield an annual savings of 196,841 liters of diesel fuel energy equivalents W it h rising fuel prices and need for quality forages implementation of perennial peanut production continues to grow in the south eastern states (French et al., 2006) These savings may be realized through the crops decreased reliance on fertilizer drought resistance, and pest

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16 tolerance, making it a viable protein and energy supplement for replacement heifer development in the southeastern U.S.A

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17 CHAPTER 2 LITERATURE REVIEW Attainment of Puberty Puberty Puberty, in beef heifers, may be defined as the first fertile ovulation, resulting in the development of a fully functional corpus luteum (CL), followed by normal estrous cycles. Beef replacement heifers should be managed so that they reach puberty early, conceive early in the first breeding season, ca lve without need of assistance, and become pregnant early with their second calf (Funston and Deutscher, 2004) Age at puberty is an economically important trait to achieve optimal lifetime productivity of a replacement heifer H eifers that become pregna nt as yearling heifers produce their first calf by 24 months of age and conceive earlier in the breeding season, continue to do so during subsequent breeding seasons, allowing for greater lifetime productivity and increased overall kilograms of calf weaned while in production (Albaugh and Strong, 1972; Lesmeister et al., 1973) In addition, prior to the breeding season, heifers that have experienced multiple estrous cycles have an increased probability for early conception (Byerl e y et al., 1987) Hormo nal Change Successful coordination of the reproductive hormones of the hypothalamic pituitary adrenal axis is critical to allow for the reproductive maturation that leads to puberty The gonadostat theory of puberty was proposed by Ramirez and McCann ( 1963), who indicated that prepubertal luteinizing hormone (LH) secretions and negative feedback from estrogen in the hypothalamic centers are critical to the onset of puberty (Day et al., 1984; 1987) As puberty approaches, the negative feedback of estrog en on

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18 the secretion of gonadotropins by the pituitary declines This coincides with an increase in LH pulse frequency (Day et al., 1984) and a decrease in amplitude (Day et al., 1987) While the mechanism for this response is not clearly understood, a reduction in the number of estrogen receptors on which estrogen exerts a negative effect on the hypothalamopituitary axis has been documented A decline in estrogen receptors has been shown in rats near puberty (Kato et al 1974), corresponding to the age in which negative feedback of estrogen declined and in heifers in the area of the medial basal hypothalamus (Day et al., 1984) Widely accepted theories support that upon estrogen binding to its receptor; it forms a receptor steroid complex This complex is then transformed and translocate into the nucleus of the target cell, causing a decline in receptor numbers (Day et al., 1987) However, this change in receptor numbers only occurs in specific tissues indicating that this maybe a result of sexual mat uration (Day et al., 1987) As early as 130 to 60 d prior to the onset of puberty the number of estrogen receptors in the hypothalamus and pitui tary remain high, but at 40 d preceding ovulation, they begin to decline and continue to do so until ovulation Concurrently, the negative feedback loop of estrogen on LH secretion begins to reduce at 40 d prior to puberty, continues to diminish at 20 d and becomes a positive feedback loop as ovulation nears (Day et al., 1987) Estrogen secretion and uterine weight also increase as puberty nears and as the negative feedback of estrogen is removed LH pulse frequency begins to increase around 40 d prior to ovulation with the LH surge resulting in ovulation. The increase in LH results from increased responsivenes s to gonadotropinreleasing hormone ( GnRH), which stimulates LH and follicle stimulating

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19 hormone (FSH) secretion, which results in increased follicle growth. Follicular development allows estrogen to reach threshold concentrations stimulating the preovul atory LH surge to induce ovulation (Day et al., 1987) When puberty approaches, an increase in responsiveness of the pituitary to GnRH occurs (Schams et al., 1981) without alterations in the number of GnRH receptors being observed peripubertal ly showing a concentration related response (Day et al., 1987) The secretion of GnRH is fundamental for the induction of puberty, with the appropriate pulse frequency and amplitude being required to stimulate gonadotropin release from the anterior pituitary The number of neurons that secrete GnRH, their morphology and distribution are well established prior to puberty However, the degree of functionality of the neurons increases dramatically prior to the onset of puberty (Senger, 2003) It w as postulated that a mechanism controlling the onset of puberty is the ability of presynaptic neurons to transmit information to GnRH neurons to elicit secretion (Senger, 2003) Presynaptic neuron function is influenced by nutritional plane, environmental and social cues, a nd genetics (Senger, 2003). Hypothalamic GnRH Neurons Prior to puberty the anterior pituitary lobe is capable of secreting FSH and LH after receiving an exogenous GnRH stimulus, with subsequent response by the ovaries via production of follicles and estrog en. Thus, the onset of puberty is not only limited by gonadal function but also the ability of the hypothalamus to produce sufficient quantities of GnRH (Senger, 2003) The development of the hypothalamus is a gradual process involving the tonic GnRH center and the preovulatory surge center In order to allow the preovulatory surge of LH stimulated by GnRH, full development of the surge center must occur by increased frequency and amplitude of GnRH secretion. In addition, the

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20 tonic center must develop as it is the regulatory system of the frequency of GnRH pulses A lack of gonadal estrogen characterizes the prepubertal females inability to activate the surge center (Senger, 2003) Follicle Dynamics In cattle, follicle growth is characterized by foll icle wave patterns, with two or three FSH induc ed waves commonly occurring in the 21 d estrous cycle (Evans, 2003), with heifers typically having threewave estrous cycles (Savio et al. 1988 ; Sirois and Fortune, 1988; Knopf et al., 1989) These waves of antral follicle growth occur in 7 to 10 d intervals (Evans et al., 1994; Sunderl and et al., 1994; Ireland et al., 2000) An increase in FSH initiates the recruitment of a cohort of 3 to 4 mm antral follicles, which is followed by the selection and develop ment of a single dominant follicle (12 to 20 mm), while the remaining follicles undergo atresia (Adams et al., 1992; Evans et al., 1994; Fortune 1994) Growth of the dominant follicle to ovulatory size (> 10 mm) occurs during the latter portion of the follicular wave The development of a dominant follicle ta kes place during dioestrus (d 6 to 12) and then again reoccurring during luteolysis (approximately d 18) of the follicular phase in a twowave cycle, with ovulation occurring on d 1 (Matton et al., 1 981) Intrafollicular ratios of estrogen and progesterone are critical in the selection, dominance and atresia, or ovulation of follicular waves (Ireland et al., 1987; Ireland and Roch e, 1987), with the number of LH receptors increasing while the number o f FSH receptors decrease during growth of estrogen active follicles during estrus and dieoestrus (Ireland and Roche, 1983) Endocrine mechanisms that lead to the emergence, growth, and selection of dominant follicles are similar between prepubertal and p ubertal heifers (Evans et al., 1994), with no known predictive indicators to the exact timing of the pubertal ovulation,

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21 or the number of follicular waves in the subsequent estrous cycle of normal duration in beef heifers (Evans et al., 1994) The developmental pattern, growth of follicles, and regression is similar in peripubertal heifers to older, cyclic heifers (Sirois and Fortune, 1988; Ginther et al., 1989) Factors Affecting Puberty Genetics Differences in age and weight at the onset of puberty hav e been established within and across breeds (Laster et al., 1972; Dow et al., 1982; Cundiff et al., 1986 ) These differences are attributed to diverse frequencies and additive effects of the genes present (Martin et al., 1992) Bos indicus and Bos indicusinfluenced breeds (those breeds with genetic crosses of Bos indicus such as Brangus Braford, and Santa Gertrudis etc.) tend to be older and heavier, with increased frame size at puberty, compared to Bos taurus heifers (Warnick et al., 1956; Temple et al ., 1961; Baker et al., 1989) Heifers of Brahman influence were older, taller, and heavier at the onset of puberty compared to Bos taurus counterparts (Stewart et al ., 1980) Crossbred heifers had increased weight and hip height at puberty compared to p u re bred heifers (Stewart et al., 1980) Regardless of Bos indicus or Bos taurus influence, breed groups with larger frame size and faster rate of gain reach puberty at a later age when compared to b reeds with a history of selection for maternal traits (Ma rtin et al., 1992) However, the correlation between age at attainment of puberty and mature size can be offset by association s with milk production, with those breeds that have been selected for increased milk yields being lighter and younger at puberty (i e., Gelbvieh, Brown Swiss and Simmental have been selected for milk vs Charolais and Chianina that have been selected for carcass traits Martin et al., 1992)

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22 The percentage of crossbred heifers reaching puberty by a certain age is greater than pure bred counter parts, with heterosis diminishing as age increases (Laster et al., 1976), and crossbred heifers developed in a pasture system reach puberty earlier (15 d; P < 0.05) than their purebred constituents (Stewart et al., 1980) Heterosis is not lim ited to across breed effects because line breeding may reduce age of puberty, accompanied by increased gains (Burgening et al., 1979) A study of 301 heifers result ed in significant differences in age at puberty among different breed types At 19.5 month s of age, 96% of Red Poll 68% of Herefords, 89% of Angus Charolais 81% of Angus x Herefords, 74% of the Brahman Angus, and 48% of Brahman Herefords had attained puberty, indicating that those heifers with Bos indicus influence were older when they attained puberty than those without Bos indicus influence (Dow et al., 1982) Weight It is well established that weaning weight and post weaning growth rate affect age and weight at which puberty is attained. Puberty may be expected to occur at a geneti cally predetermined weight and size for each individual heifer There was a positive correlation for weight and hip height at puberty (r2 = 0.77, P < 0.01; Nelsen et al., 1982) The general dogma associated with the onset of puberty is that at approximat ely 60 to 66% of a heifers mature body weight (BW) in dependent of frame size, puberty will be attained (Patterson et al., 1992) However, additional reports do not support this critical BW hypothesis (Brooks et al., 1985), or the 60 to 66% theory (Patte rson et al., 1992) A three year study (n = 240) of Bos taurus heifers indicated that there were no differences in reproductive or calf performance in heifers developed to reach 53% of their mature BW in comparison to those heifers that were developed to reach 58% of their mature BW (Funston and Deutscher, 2004) In addition, the

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23 increased costs of development for higher target weight heifers yielded no economic return (Funston and Deutscher, 2004) Age In evaluation of genetic linages selected for use in the beef industry, age at puberty is critical and indicates that there is a minimum age that must be achieved for puberty to occur (Laster et al 1972) Age at puberty is influenced by level of nutrition (Hansel, 1959; Wiltbank et al., 1969) and prepubertal gains (Reynolds et al., 1963; Short and Bellows, 1971; Laster et al., 1972) Age at puberty is a moderately heritable trait (h2 = 0.43) with associations to weaning weight and yearling weight (Brinks, 1994) The mean age of first CL formation in 83 Bos indicus heifers was 19.4 months, with a range of 14 to 20 months (Plasse et al., 1968) There also was a corr elation between weaning weight, age at puberty (r2 = 0.21; P < 0.01; Ari je and Wiltbank, 1971), and 205day weights (r2 = 0.41; P < 0.01; Plasse et al., 1968) In addition, heterosis was negatively correlated ( P < 0.05) with age at puberty (Nelsen et al., 1982) and the age at which estrogens negative feedback system on gonadotropin secretion begins to decline can be influenced by diet, al lowing for nutritional induced precocious puberty to occur (Kurz et al., 1990; Gasser et al., 2006) Body Composition A critical amount of body fat may be required for attainment of puberty Peripubertal increases in adipose tissue have been reported in beef heifers, in comparison heifer s prepubertal body composition (McShane et al., 1989; Buckley et al., 1990) H owever these changes could have been a result of breed and nutritional status (Brown et al., 1972; Carstens et al., 1991; Keele et al., 1992) In contrast, no

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24 abrupt changes in body compos ition have been reported 75 d prior to puberty (Hall et al., 1995) In many experimental models dietary energy and interaction of breed modify the rate of change of body composition Increased rate of gain results in a greater BCS, carcass weight, fat thickness, and total separable fat at puberty ( Brook s et al., 19 85 ; Hopper et al., 1993; Yelich et al., 1995) In addition, hormonal and metabolic changes which alter body composition may regulate LH secretion, a key component hormone responsible for the attainment of puberty (Schillo, 1992) The whole body energy balance hypothesis proposes that availability of total body energy modulates the activity of GnRH pulse generators, regulating ovulation (Bronson and Manning, 1991) Thus, body composition may not be a sole regulator of attainment of puberty but is directly associated with many hormones and metabolites (Yelich et al., 1995) Metabolic Indicators The reproductive axis is more sensitive to nutrient availability then the growth axis (Hileman et al., 1991), therefore attainment of a specific metabolic status by cattle may be critical to the onset of puberty which is characterized by several metabolites and hormones such as glucose, insulin, and insu lin like growth factor I ( IGF I ; Steiner et al., 198 7 ) Blood urea nitrogen (BUN) and insulin at puberty indicated that heifers were at differing metabolic states at the onset of puberty (McShane et al., 1989) While insulin and BUN concentrations differ ed throughout the prepubertal period, only insulin increased as puberty neared (Hall et al., 1995; McShane et al., 1989), indicating that BUN app ears to be unrelated to puberty and is more a function of diet (Kennedy, 1980) and rate of protein degradation (McShan e et al., 1989) I nsulin can be influenced by feed intake and dietary energy density (Bassett et al., 1971; Richards et al., 1989), with

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25 dry matter intake being proportional to BW (NRC, 1984), thus increases in insulin could also be linked to DMI and diet. M etabolic factors are highly dependent on diet composition and feed intake and as heifers near puberty increases in BW may lead to increased intake, resulting in differing concentrations in plasma of glucose. Alterations in rumen fermentation p atterns and volatile fatty acid profiles have been reported to alter LH secretions Increases in propionate, the key component of gluconeogenesis in the ruminant, are reported to increase LH pulse frequency and amplitude (Moseley et al., 1977; Rhodes et al., 1978; McCartor et al., 1979) Decreasing concentrations of insulin are associated with decreased LH concentrations (McCann and Hansel, 1986); however exogenous insulin does not increase LH secretion (Hileman et al., 1993) It has been reported that as puberty nears, glucose concentrations are not altered; however, hypoglycemia has been reported to decrease LH pulsatility in ovariectomized ewes (Clarke et al., 1990) and decreased LH pulse amplitude in intact cows (Rutter and Manns, 1987) In addition, greater postpubertal concentrations of glucose were noted in heifers compared to prepubertal heifers (Verde and Trenkle, 1987) When no alteration in glucose concentrations were reported, a decrease in serum concentrations of insulin from 40 to 17 d pr ior to puberty was observed, indicating possible increases in peripheral tissue sensitivity to insulin at puberty with a link to an increased LH pulse frequency in Angus heifers (Jones et al., 1991) In addition, as insulin concentrations decreased prior to puberty, an increase in free fatty acids (FFA) was reported (Jones et al., 1991) Concurrently, prepubertal increases of I G F I may reflect increased activity of the hypothalamic hypophyseal ovarian axis, with follicular

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26 fluid containing abundant quanti ties of insulin like growth factor I ( I G F I ; Hammond et al., 1988) Time of Gain When gain was delayed until the last half of development there were no negative effects of reproduction in heifers, and while heifers may weigh less throughout the development process, there was no difference in BW or age at the onset of puberty, with similar first service conception and overall pregnancy rates (Clanton et al., 1983) In addition, heifers that gained late in the development phase had significantly reduced fe ed inputs and DMI compared to heifers with a constant ADG, with no differences in body condition score (BCS) or back fat thickness determined by ultrasound. Pelvic area and frame score at the conclusion of the breeding season also were similar, indicating that no effect on skeletal development was observed (Lynch et al., 1997) However, Yelich et al (1995) reported that heifers that gained at a highsteady rate of gain had increased BCS and BW at puberty, with decreased age of puberty, which were similar to previous reports (Arije and Wiltbank, 1971; Short and Bellows, 1971) Underfeeding, resulting in low weight gains or weight loss throughout the development phase was reported to delay the onset of puberty (Wiltbank et al., 1966, 1969; Day et al., 1986) Rate of Gain Body weight and age at puberty are influenced by nutrient intake (Short and Bellows, 1971) Heifers fed to gain at a higher ADG had a significantly greater number of females cycling prior to the breeding season (85% vs 74%; P < 0.01; Funst on and Deutscher, 2004) Similarly heifers on a high weight g ain diet reached puberty 43 d younger than those on moderate or slow gain diets (Hall et al., 19 95) High gain heifers also had increased instances of calving diffi culty with reduced adjusted 2 05d weights of

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27 their calves at second calving (Funston and Deutscher, 2004) Increased ADG resulted in increased lipid depots and total percentage of carcass weight being lipids ( Waldman et al., 1971; Kempster et al., 1976), which may be linked to the onset of puberty by the critical body fat hypothesis ( McShane et al., 1989) In addition, it is hypothesized that limit feeding, compared to programmed feeding in which an energy equation is used to meet nutrient requirements plus provide for desired gains, may improve cow herd efficiency through the development of replacement heifers on an accelerated rate of gain This accelerated gain results in heavier mature cow weights, making rate of gain during development a possible tool to manipulate mature cow si ze and nutrient requirements (Galyean, 1999) Plane of Nutrition Increasing planes of nutrition resulted in decreased age of puberty, with lighter weights and smaller body frames ( Wiltbank et al., 1969; Stewart et al., 1980) In addition, interactions between breed type and plane of nutrition exist ( P < 0.05) for age, height, and weight at puberty (Nelsen et al., 1982) Low planes of nutrition or negative energy balance inhibits LH secretion through both estrogen dependent and ovarian independent mecha nisms (Kurz et al., 1990) Predicting Puberty After analysis of 353 Bos taurus heifers, prediction equations were developed for age and weight of puberty, and the regression of age and weight of puberty on birth date, actual weaning weight, and ADG (Arij e and Wiltbank, 1975) The accuracy of these equations was then validated using two sets of unrelated, known puberty data Age at puberty was similar but lower than observed data in one experiment and not different in the subsequent experiment, with the same being true for weight at puberty,

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28 revealing that mathematical and statistical equations may be useful however lack complete accuracy in the prediction of the onset of puberty (Arije and Wiltbank, 1975) Reproductive tract scoring (RTS) was developed as a means to assess age at puberty indirectly (Anderson et al, 1991) on a five point scale. A RTS of 1 is an immature, prepubertal repro ductive tract, with 5 being a reproductively mature heifer that is cycling and has a CL. With adjustments for BW and age, RTS was positively correlated with pregnancy rate ( P < 0.01), calf weaning weight (r2 = 0.22, P < 0.01) and negatively associated with days to calving (r2 = 0.28, P < 0.01) in replacement heifers The RTS of heifers was associated with age, BW and BCS, with the strongest association being to age (Holm et al., 2009) Concepts of Nutrition Effect of Nutrition on Reproduction Low energy diets are associated with reduced concentrations of pituitary hormone ( Rutter and Randel, 1984; Imakawa et al., 19 86) and poor reproductive performance (Rakestraw et al., 1986; Perry et al., 1991; Wiley et al., 1991) Heifers with an increase in ruminal propionate concentration ( P < 0.01) reached puberty at 29.5 d younger ( P = 0.009) and weighed 17.2 kg less ( P = 0.0 3) those heifers with increased acetate to propionate ratios ( McCartor et al., 1979) In addition, maternal nutrient restriction has been shown to have an impact on the reproductive performance of female offspring A 19 d increase in age at puberty was r eported in offspring of prepartum energy restricted dams (Corah et al., 1975) and altered adrenal steroid production in ewes restricted in late gestation (Bloomfield et al., 2003); however, additional research contradicts these studies stating that there w as no observed differences in age of puberty of maternally restricted heifers ( P = 0.15; Martin et al., 200 7 ) Therefore, proper understanding of

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29 intake, supplementation of replacement heifers, and synchrony of nutrients is critical in the success of repr oductive performance and development Regulation of Intake The control of feed intake is multifaceted with alternate and redundant mechanisms working through the feeding center of the brain (Allen et al., 2009), and despite decades of research there is still no unified explanation of intake regulation (Forbes, 2007) Clearance of digesta from the rumen has been indicated to be the primary factor limiting intake by ruminants (Ulyatt et al., 1986) as suggested by the physical theory (Forbes, 1996) with total DMI being highly correlated (r2 = 0.98) to rate of passage from the rumen (Guthrie and Wagner, 1988) This is thought to be regulated by the sensitivity of receptors in the rumen wall which respond to stretch and touch, where intake is suppressed when the capacity of the rumen is reached (Allen, 1996) As a result, improvements in forage intake may be noted when rate of digestion, rate of passage, or both are improved (Moseley and Jones, 1979) Rumen retention time is dependent on the extent of cell wall digestion, in conjunction with quantity and quality of fiber, as a function of the rate of passage of digesta ( Ro b ertson and Von Soest, 1975 ; Staples et al., 1984) The hepatic oxidation theory (HOT) hypothesizes that feed intake is regulated by sig nals from the liver to the brain that are stimulated by oxidation of various metabolic fuels (Allen et al., 2009) The inhibition of glycolysis and fatty acid oxidation (Friedman and Tordoff, 1986), blocking glycolysis and lipolysis (Friedman et al., 1986) increased feed intake in rats Physiologically this is supported by association of the liver with afferent and efferent hepatic vagal fibers, allowing for crosstalk with the central nervous system to convey energy status which results in feeding behavi or changes through

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30 alterations in firing rate of neurons (Berthoud and Neububer, 2000) Amalgamation of the two theories would imply that when a diet is low in caloric density it is likely that gut fill will elicit the satiety effect; however, in a high energy diet energy balance via HOT is likely the signal In addition, hormones have been noted to influence feed intake i n cattle, with the two of primary hormones being ghrelin and leptin Ghrelin, a peptide hormone synthesized by the abomasal and ruminal tissues of cattle, has been shown to stimulate feed intake through neuropeptide Y (NPY) and agouti related protein (AGRP; Inui, 2001; Nakazato et al., 2001; Shintani et al., 2001) In fasted steers, the average plasma ghrelin concentration was elevated ( P < 0.05 ) compared to steers on feed, with no differences in glucose concentrations (Wertz Lutz et al., 2006) In contrast, leptin has been shown to reduce food intake (Morrison et al., 2001) As a hormone that works to control body homeostasis and reg ulate appetite, leptin is implicated in metabolic regulation through its action on the hypothalamic pituitary adrenal axis activity and on reproductive activity (Keisler et al., 1999) Concentrations of leptin are positively correlated to adipose tissue l eptin mRNA (Amstalden et al., 2000) such that administration of leptin will reduce feed intake in ruminants (Morrison et al., 2001) Variations in leptin concentrations in ruminants of 17 and 35% were explained by adiposity and nutritional status (Delava ud et al., 2000), with 37% being accounted for by BCS in lactating cows (Ehrhardt et al., 2000). Insulin has also been shown to have an effect on feed intake, with infusion of low levels of insulin exogenously resulting in an increase in feed intake most l ikely as an effect of the increased rate of fat deposition and growth, however it is likely that insulin

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31 is not a primary regulator of intake (Forbes, 2000) but an integrate d system of several control mechanisms Energy Energy in feed is derived from the denaturation and manipulation of protein, carbohydrates, and lipids, each of which have a relative cal oric density of 5.6 kcal/g, 4.2 kcal/g, and 9.4 kcal/g, respectively Energy supplies are used first to meet the maintenance requirements of the animal, followed by partitioning for production (NRC, 2000), with maintenance being influenced by level of feeding, previous plane of nutrition and breed (Grah am and Searle, 1972; Gray and McCracken, 1979; Ferrell et al., 1986) A truncated list of reasons for differences in maintenance requirements that are seen includes: physiological status (Ferrell and Oltjen, 2008), season (Senft et al., 1987), confinement (Osuji, 1974), breed (Laurenz et al., 1991), digestive and metabolic efficiencies (Grovum, 1986), and environment (NRC, 2000). In ruminants energy is supplied primarily by the fermentation of ingested organic matter to volatile fatty acids (VFA) followed by ruminal absorption, and some post ruminal absorption. The fermentation of glucose results in pyruv ate molecules which are converted into VFA as an energy source. In the reduction of pyruvate to the primary VFA (propionate, acetate, and butyr ate) differences in efficiency exist (Stewart et al., 1997) For energy supplementation, carbohydrates are the primary energy substrate fed to cattle Carbohydrates are classified into two groups: 1) nonstructural carbohydrates (NSC), such as starches, that are highly soluble, leadi ng to rapid rates of digestion and increased rate of passage; and 2) structural c arbohydrates (SC) which are contained within the cell wall of plants These cell walls are composed of hemicellulose, cellulose, lignin, and pectin, which have slow rates of digestion and passage. The NSC are often

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32 fed to increase the energy density of a diet (Huntington, 1997), consisting primarily of grains and concentrates The NSC are highly fermentable substrates that typically cause a shift in the acetate to propionate ratio, with a greater proportion of propionate being produced, resulting in a de cline in ruminal pH Feeding NCS such as corn alters the microbial population of the rumen, shifting ruminal conditions to favor amylolytic bacteria and decreasing functionality of cellulolytic populations typically as a result of decreased ruminal pH r esulting in a reduction of fiber digestion The reduction of intake that accompanies this effect is likely due to subacute acidosis (Mould and Orskov, 1983) When pH ranges from 6.7 (Mertens, 1977) to 6.2 (Mould et al., 1983) or lower, SC digestion may d ecline. Ruminants that consume high concentrate diets (NSC 70% concentrate) typically has a ruminal pH that ranges from 5.8 to 6.6, whereas those on a foragebased diet range from 6.2 to 6.8 (Church, 1979) When heifers receiving a 75% c oncentrate diet were co mpared with those received a 75% alfalfa ( Medicago sativa L.) diet t hose consuming the concentrate diet ingested less dry matter, energy, and nitrogen, while producing less heat and retaining more tissue energy in addition to decreased portal drain viscer a blood flow and O2 uptake by the liver (Blaxter, 1980; Reynolds et al., 1991) This concurs with reports indicating that high NSC diets were utilized more efficiently by ruminants ( Blaxter and Wainman, 1964; Garrett, 1979) In addition, the increased pr opionate levels that are associated with NCS feeding (Reed et al., 1997) hav e been shown to be beneficial for reproductive hormone secretion such as LH (Bushmich et al., 1980; Randel and Rhodes, 1980; Randel et al., 1982) and reproductive performance ( McCa rtor et al., 1979; Hardin and Randel, 1983; Lalman et al., 1993) The readily available energy from

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33 starch fermentation also increases ruminal outflow of microbial protein in cattle (Spicer et al., 1986; Streeter et al., 1989; Poore et al., 1993) Prote in Supplementation of protein to cattle consuming lower quality forages comprises a substantial portion of annual feeding costs in the cow calf sector of beef production (Wickersham et al., 2008) In an effort to decrease cost and labor, alteration in protein supplementation frequency has been explored under the hypothesis that nitrogen recycling will support ruminal fermentation needs between supplementation events (Currie r et al., 2004 a ) Decreased supplementation frequency maintained desired growth per formance (Bohnert et al., 2002) with minimal impact on nutrient intake and digestibility (Beaty et al., 1994; K ster et al., 1997 ) Reductions in BCS and BW have been reported when supplements were fed less frequently but offered similar total protein (Beaty et al., 1994; Currier et al., 2004b ; Farmer et al., 2004 ) However, with decreases in frequency of supplementation, decreases in forage intake were observed (Bohnert et al., 2002; Farmer et al., 2004 ) These decreases were reported particularly on the day of supplementation ( P < 0.01; Cooke et al., 2007), and accompanied by significant alterations in microbial populations and differing lag times of fermentation, or the time from which the ingested feedstuff enters the rumen until attachment of microor ganism s and penetration to initiate digestion (Farmer et al., 2004) A positive effect of protein or nitrogen supplementation on intake or utilization with forages has been recognized (Church and Santos, 1981; Coleman and Wyatt, 1982; Hennessy et al., 1983 ) When steers received protein supplement (soybean meal) with a low qual ity prairie hay (4% CP) diet increased ( P < 0.01) digestibility of dry matter, organic matter, crude protein, cellulose, and increased concentrations of ruminal NH3

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34 were noted com p ared with those not receiving the protein supplement (Guthrie and Wagner, 1988) Nutrient Synchrony Developing an integrated system between protein and energy (carbohydrates) digestion to maximize nutrient utilization and microbial yields substantially i mproves performance of ruminants (Nocek and Russell, 198 8 ) With nutrient availability being determined by the extent and rate of digestion in the rumen, microbial populations and yields are critical Microbial yields are a function of energy (Bauchop and Elsden, 1960) and nitrogen availability in the rumen When ATP is available (primarily from carbohydrate fermentation) amino acids are incorporated into microbial protein; however, when there are insufficient carbohydrates to match protein in the rumen protein nitrogen is deaminated, increasing ruminal NH3, which may enter the urea cycle rather than being incorporated into microbial biosynthesis (Hogan, 1975) Therefore, the rate of digestion of energy carbohydrates and nitrogen must be synchronized t o optimize microbial biosynthesis The f eeding of structural and nonstructural carbohydrates, which differ s in rate of digestion, must be matched with the rate of digestion of the protein source provided to maximize the performance and microbial protein yield (Nocek and Russell, 198 8 ) The synchronization of starch and protein degradation reduced NH3 absorption and increase d nitrogen retention in steers (Taniguchi et al., 1995) and lambs (Matras et al., 1991) In addition, microbial protein flow into the duodenum increased in a linear fashion as the level of protein supplementation increased (Wickersham et al., 2008)

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35 Associative Effect s When a diet is formulated, it is assumed that each ingredient will have a positive contribution to the nutritional v alue of the diet; however, this is not always the case Associative effects describe the nonlinear response in the utilization of two nutrients when combined together (Moe, 1979), compared to when the same feedstuffs are fed individually Typically diet s are calculated with linear equations, and do not account for the associative effects that are present True associative effects on digestibility are difficult to determine due to their strong link to intake which is confounded by digestibility data (Church, 1988) Negative associative effects often occur in forageconcentrate diets (Lamb and Eadie, 1979; Vadiveloo and Holms, 1979) Depressions or reductions in digestibility of starch, protein and NDF account ed for 57, 12, and 32% of the total depress ion of digestibility, respectively, in high intake scenarios with associative effects (Church, 1979) An 8.9% deviation in the predicted net energy of gain in corn silage diets containing 30 to 70% added corn has been documented (Woody et al., 1983) In addition, a positive associative effect with high quality alfalfa and soybean stover was reported (Soofi et al., 1982) An associative effect of increased forage digestibility was reported when protein was supplemented (Gallup and Briggs, 1948), and conversely, carbohydrate supplementation decreased cellulose digestion of corncobs and timothy hay (Burroughs et al., 1949) Nitrogen Recycling and Blood Urea Nitrogen The tissues of the digestive tract account for 25 to 40% of whole body protein synthesis, accounting for a small portion of exchanges and transactions involving nitrogen metabolites (Lobley, 1993) Urea recycling has a considerable role in nitrogen

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36 supply to the rumen and the animal, especially when supplementation of high protein feedstuffs occurs infrequently (Wickersham et al., 2008) Ruminal bacteria require ATP and a nitrogen source for microbial synthesis and most bacteria species are able to use NH3N as a source of nitrogen for growth, however, specific N sources are required and can be limiting factors for specific microbial populations. In general, most microorganisms can use ammonia and a carbon source to synthesize the amino acids required for growth (Bryant and Robinson, 1962) With all the essential amino acids being synthesized by the rumen microbial populations (Loosli et al., 1949), indicating that protein in a ruminant diet could be replac ed with nonprotein nitrogen (N P N ) without affecting the animals protein supply However, lambs whose N sources was limited to only urea, had growth and efficiency that was reduced 70% (Clifford and Tillman, 1968) when compared to lambs fed i solated soy protein. I ncreases in production have been seen when perc entages of a dietary protein were replaced with NPN (Flatt et al., 1967) Thus, complete replacement of dietary protein with NPN reduces animal performance, but replacing protein nitrogen with NPN at certain levels may improve ruminal efficiency. This is likely due to the fact that some species of bacteria can use ammonia as their s ole N source while others have substantial improvement in bacterial protein yields when supplemented with preformed amino acids, showing that some bacteria have a requirement for amino acids and or peptides (Br yant and Robinson, 1962; Hume and Brid, 1970; Maeng et al., 1976) Selenomonas ruminantium, Bacteroides ruminicola, Megasph aera elsdenii Streptococcus bovis, and Butyrivibrio fibrisolvens are found in the rumen in large quantities under various feeding conditions, and differ in response to NPN and amino

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37 acid levels in the rumen. Bacteroi des ruminic ola and Megasph aera elsdenii yields were not affected by a reduction to amino acid supply in the rumen, while removal of amino acids from the diet greatly suppressed Selenomonas ruminantium and Streptococ cus bovis (Cotta and Russell, 1982) Microbial protein synthesis provides for 50 to 80% of the protein that is supplied to the small intest ine of the ruminant (Storm and rkskov, 1983) Blood urea nitrogen (BUN) is a useful indicator of the protein util ization and status of an animal There is a strong linear relationship between BUN and nitrogen excretion in several species, therefore, BUN may be used as an indicator of nitrogen utilization, fecal nitrogen, and intake nitrogen with estimates of intake, retention and digestibility of diets (Kohn et al., 2005) Transfer of endogenous BUN into the rumen supplies substantial quantities of nitrogen to ruminal microorganisms (Egan, 1980) Approximately 40 to 80% of the ureanitrogen synthesized in the liver is returned to the gut to support microbial protein synthesis (Harmeyer and Martens, 1980) The total proportion of BUN incorporation into the microbial population of the rumen is inversely linked to the level of protein intake (Bunting et al., 1989), and nitrogen intake in growing cattle is correlated with hepatic ureagenesis (r2 = 0.58) with synthesis ranging from 49 to 178% (mean of 93%) of digested nitrogen (Lapierre and Lobley, 2001) The magnitude of reuptake by the rumen of urea as a nitrogen sou rce for the synthesis of the microbial population has been suggested to be driven by BUN concentration (Harmeyer and Martens, 1980); however, contrasting data indicates that concentration dependent transfer across portal

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38 drain viscera is only applicable at a 4 m M plasma urea concentration for cattle (Lapierre and Lobley, 2001; Lobley et al., 1998) As supplementation of ruminal degradable protein increased there was a linear increase ( P < 0.006) in production and gut entry of urea, microbial flow of nitr ogen ( P < 0.001), and incorporation of recycled ureanitrogen was greater when protein was supplemented less frequently in higher quantities (Farmer et al., 2004; Wickersham et al., 2008)

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39 CHAPTER 3 EFFECTS OF FEEDING P ERENNIAL PEANUT HAY ON GROWTH, DE VELOPMENT, ATTAINMENT OF PUBERT Y, AND FERTILITY IN BEEF REPLACEMENT HEI FERS In the beef cattle industry t wo thirds of the annual cost of production is associated with the cost of feed (Arthur et al., 2001) emphasizing the importance of successful replacement deve lopment to minimize the time a heifer enters a herd until she becomes a productive cow For this to occur, replacement heifer s m ust be well managed to optimize their lifetime productivity and future profitability of all females Critical analys e s of nutritional and reproductive fac tors that influence the growth and reproductive maturation of replacement heifers have revealed benchmarks that serve as guidelines for beef heifer development that most producers adhere to Decades of research have led to the conclusion that BW (Nelsen et al., 1982), body composition (Buckley et al., 1990), age (Laster et al 1972) and genetics (Baker et al., 1989) are critical components to the attainme nt of puberty Selection by producers can control age at which a replacement heifer enters the development program, in addition to genetics, allowing the remaining factors that affect puberty to be managed nutritionally In the southeastern United States, typ ical rations that are used for heifer development scenarios are not available due to limitations of commodities and lack of availability of high quality legume forage. Thus, alternative feeds are being explored as an option for replacement heifer diets A forage source that is gaining popularity and availability is perennial peanut f orage ( Arachis glabrata Benth.) As a warm season leg ume, it is grown in the southeastern United St ates for use as hay silage, and improved pasture land Similar to alfalfa ( Medicago sativa L.) in nutritive value and a ppearance (My er et al., 2009), perennial p eanut forage has typical yields of 1, 145 to

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40 1,908 kg per hectare, with approximately 12,140 hectares being planted in N orth Florida and South Georgia (Hill, 2002 ; Newman et al., 2009) Thus, perennial peanut hay has potential for incorporation into replacement heifer feeding strategies due to its increasing availability in the southeastern United States and high nutritive values (TDN = 60%; CP = 14%; Myer et al., 2009) The objective of this study was to determine the influen ce of supplemental feeding of perennial peanut hay on growth performance and age at puberty in gr owing beef cattle heifers It was hypothesized that heifers r eceiving perennial peanut hay as their su pplementation would have similar or improved growth perf ormance and attain pubert y at a similar age compared to contemporaries supplemented with a grain based concentrate supplement Materials and Methods Animals and Treatments All a nimal handling and care was approved and performed according to Institutional Animal Care and Use Committee guidelines under protocol 200902813 and funded by the USDA TSTAR C grant (project number FLA NFC0049934) During two heifer development and breeding seasons 120 Bos indicus Bos taurus crossbred, spring born heifer calves at the North Florida Research and Education Center in Marianna, Florida (30.8406191 Lat and 85.1659651 Long .) were used for this study The climate at this location is subtropical / temperate with hot humid summers and cool winters Breeds origin of crossbred heifers were Angus, Brahman, Charolais, Beefmaster, and Romosinuano. The mean age of the heifers at the initiation of year 1 (Yr1) was 270 21. 7 d (mean SD) of age (DOA) and mean body weight (BW) was 244 23. 7 kg (mean SD), in year 2 (Yr 2) the mean DOA was 255 23.9 d (mean

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41 SD) with a m ean body weight ( BW ) 226 29.7 kg (mean SD) Heifers were weaned on August 28, 2009 for Yr1 and on July 29, 2010 for Yr2. All heifers were managed as a single herd from weaning until the initiation of the experiment (d 0) on October 20, 2009 (Yr1) and October 19, 2010 (Yr2) The experiment consisted of two separate phases: the development phase (d 0 to 140 ; phase in which treatments were applied) and the breeding phase (d 141 to 224; phase in which hei fers were comingled for breeding ). A generalized randomized complete block arrangement was used with pen serving as the experimental unit, with 5 heifers per pen for 12 pens, resulting in 4 replicates per year per treatment Within year, heifers were bloc ked by weight and pen (1.3 Ha paddock with limited to no forage availability for grazing and no shelter ), and then randomly assigned to one of three treatments: perennial peanut hay ( Arachis glabrata Benth.) supplementation (PPH), 80% Corn and 20% soybean meal (44%) supplement (CSBM), or no supplement control (CON) The CSMB was fed to average 1.23 kg.hd1* d1 and the PPH was fed at 2.74 kg.hd1* d1 ( DM basis) of each respective supplement (Table 3 1 ). All heifers received ad libitum access to water vi a automatic troughs and bermudagrass ( Cynodon dactylon (L.) Pers. ) hay (BGH) fed round bales in ring feeders A complete mineral supplement was provided for ad libitum consumption but formulated for 0.11 kg.hd1.d1 daily intakes Mineral supplement for PP H differed from that for CON and CSBM to account for differences in mineral levels supplied by the diets (Table 3 2 ). Each year, every 28 d during the developmental phase, heifers were fasted for at least 16 hr prior to measurement of BW body condition sc oring (BCS), and collection of

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42 blood samples (Figure 3 1) The BCS was assigned by the same trained individual for both years of the experiment, and was based on a 1 to 9 point scale (1 = emaciated to 9 = obese; Wagner et al., 1988) All heifers received dietary supplement treatments for a 140d developmental phase, prior to the initiation of the breeding phase In Yr2, on d 28 a heifer from the control treatment was removed from the study because of an injury She was replaced with a heifer of similar BW and age. Data from the replacement heifer was not included in statistical analyses In addition, in Yr2 a second heifer from the control treatment died during the breeding season phase; therefore, data associated with the development phase was included for statistical analyses, in addition to puberty data, as she reached puberty before death. All other fertility data was excluded from the analyses All weather data was reported as means of the 28 d periods as indicated by the Florida automated weather network for the Marianna, Florida location. Feed Sample Collection and Analysis Near infrared reflectance s pectroscopy (NIR) was used for analyses of dry matter (DM), crude protein (CP), total digestible nutrient (TDN), acid detergent fiber (ADF), neutral detergent fiber (NDF), c alcium (Ca), and phosphorous (P ) on all representative samples of supplements and BGH prior to the initiation of the experiment each year (Dairy One Forage Laboratory, Ithaca, NY) Rations were formulated to be offered on an isocaloric bas is assuming constant daily DMI and assuming that differences in BGH intake, accounting for differences in supplement TDN intake to meet the requirements of a 230 kg beef heifer growing at 0.5 to 0.7 kg per day (NRC 2000) Heifers in the CSB M and PPH treatments received supplements in each pen 3 per week (Monday, Wednesday, and Friday) Ad libitum access to BGH was allowed for all treatments

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43 throughout the development phase After completion of the development phase all heifers received 1.81 kg.hd1.d1 of 50% corn gluten and 50% soybean meal supplement (Table 3 3), wi th ad libitum access to BGH and water for 13 d (Yr1) or 21 d (Yr2) until annual r yegrass ( Lolium perenne L.) pastures had sufficient growth to support all heifers grazing together until completion of the breeding season Weekly samples of the PPH were taken from each pen to determine average weekly DM of the PPH supplement and a monthly composite sample of the CSBM was taken to determine monthly DM percentage of CSBM deliver ed. All samples were bagged and frozen immediately after collection until drying Bermudagrass hay round bales were individually weighed, with four core samples taken on the same day the weight was recorded and composited. Samples were stored for futur e analysis following grinding and composition Orts where collected for each individual round bale and subsampled for DM analysis to determine DM disappearance in each pen. All feed s amples analyzed for nutritive values were dried at 55C for 48 hr in a f orced air oven. Or ts were dried at 100C for 72 hr because of their high er moisture content At the conclusion of the drying period all samples were ground in a Wiley mill (Arthur H Thomas Company, Philadelphia, PA, USA) using a 1.0 mm screen. After grinding, samples were composited for analysi s on an equal weight basis Core samples from bermudagrass bales fed within a 28d period were composited within each pen and then composited among pens within each 28d period. These samples were combined int o a yearly sample of round bale cores to be analyzed for the

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44 developmental phase. In Yr1 116 round bales were fed with a mean DM weight of 344 41.6 kg and in Yr2 79 round bales with DM weight of 421 65.2 kg were delivered. Similarly, DM was analyzed f or the weekly PPH samples that were taken from each pen Samples were ground and composited into a weekly sample which was composited by 28d period, with each 28d period sample combined into a single PPH sample to determine the nutritive value of PPH supplement for each year Representative samples of CSBM were taken every 28d of the feeding phase of each year and were analyzed for DM and composited to generate a single CSBM supplement sample for nutritive analysis across all experimental units for thi s treatment All nutritive value samples (round bale cores, CSBM, PPH and ryegrass ) were analyzed for D M, CP, TDN, ADF, NDF, Ca, and P in duplicate by a commercial laboratory using N I R procedures (Dairy One Forage Laboratory, Ithaca, NY) Blood Collect ion and Analyses Blood samples were collected weekly for analysi s of progesterone concentrations In addition, blood samples were collected every 28d for analysi s of blood urea nitrogen (BUN) concentrations Blood was collected via jugular or coccygeal venipuncture using 10 mL glass vials containing 143 IU units of Na heparin (BD Diagnostics, Franklin Lakes, NJ) All blood samples were placed on ice following collection, and then centrifuged for 18 min at 4 000 g at 4 C After centrifugation a pipet te was used to siphon plasma into polypropylene vials (12mm 75mm; Fisherbrand; Thermo Fisher Scientific Inc., Waltham, MA) which were stored at 20 C until analyses. Concentrations of plasma progesterone were determined by competitive binding enzyme lin ked immunosorbant assay (ELISA) to determine pubertal status The ELISA procedure was ado pted from that previously described by Rasmussen et al (1996)

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45 Quality controls were established using 100 l plasma with a known progesterone concentration of 2.5 ng/mL Standards were determined with 0.1, 0.2, 0.5, 1.0, 2.0, 5.0, 10.0, and 20.0 ng/mL concentrations with a duplicate of each respective standard Assay sensitivity for a 100 L sample was 0.1 ng/mL. Pooled samples revealed that the intra and inter assay coefficient of variation were 7.0 % and 19.0% for 29 assays, respectively Analysis of BUN was determined via a QuantiChromTM Urea Assay Kit (DIUR500; BioAssay Systems,Hayward, CA) No dilution was used during the analysis and samples were not de emed to be low value samples Standard samples revealed that the intra and inter assay coefficient of variation was 2.0 % and 5. 4 % for 22 assays, respectively for BUN analysis Assessment of Puberty To determine puberty, the first increase in progesterone (evidence of first pubertal ovulation) that exceeded 0.5 ng/mL followed by a progesterone pattern consistent with normal estrous cycles was the criteria used for assessing age at attainment of puberty (Perry et al., 1991) Age of puberty (AOP) was defi ned as the age of the heifer at the first rise in progesterone. Weigh t at puberty was the BW associated with the onset of puberty and was calculated using average daily gain (ADG) during the 28d period associated with the onset of puberty The equat ion for weight at puberty was: l ast 28d weight before onset of puberty + (average daily gain during the 28d period associated with onset of puberty days from last 28d weight to onset of puberty) For both Yr1 and Yr2, weight data collection ceased on d 2 24 after initiation of heifer development and coincided with the last week of the breeding phase Blood collection ceased 21 d following All heifers that had not attained puberty were assigned an onset of puberty

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46 age to coincide with the last day of the data collection period (d 245) In Yr1 4 heifers had not attained puberty and in Yr2 7 heif ers had not attained puberty prior to the conclusion of the study Temperament Characteristics In Yr2, chute score (CS), exit velocity (EV), and pen score (PS) w ere temperament traits that were evaluated using procedures previously described by Arthington et al (2008) Chute score and EV were assessed every 28 d and PS was assessed on d 84 and 140 of the development phase The subjective measurement of the behavioral response to restraint within the squeeze chute (CS) was assigned on a 1 to 5 scale (1 = calm, docile, and quiet; 2 = restless; 3 = nervous; 4 = excited and flighty; 5 = aggressive) by a trained evaluator Exit velocity was the speed (m/s) at which each heifer exited the squeeze chute and passed by LED optical sensors placed at a distance of 1.83 m apart Pen Score was a subjective measurement of the animals behavioral response to isolation in the pen with a handler present Three trained evaluat ors assigned scores on a 1 to 5 scale (1 = calm, docile, a nd quiet; 5 = aggressive) that were used to compute a mean score for each animal Reproductive M anagement During Yr1 and Yr2, on d 140 (the conclusion of the development phase) the breeding phase was i nitiated (Figure 3 2) by comingling all heifers and managing them as a single herd. On that day, each heifer received a 25 mg i ntramuscular (i .m.) injection of prostaglandin (PGF) and an EstrotectTM heat detection aid (Rockway Inc, Spring Valley, WI) was placed on the tailhead of each heifer to assist with detection of estrus Estrus detection was preformed 2 per day at 0700 and 1600 hr for 45 min during each session Each heifer detected in estrus was inseminated artificially by an

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47 experienced technician using the AM/PM rule (Larson et al., 2009) Heifers that were not detected in estrus within 11 d of the initial injection of PGF received a second 25 mg injection of PGF i.m followed by detection of estrus for a further 6 d. Natural service sires were introduced into the herd 17 d after initiation of the breeding phase and remained in the herd for 60 d. In Yr1 two mature si res were used and in Yr2 three yearling sires were used, all sires passed a breeding soundness exam before introduction into the herd. Pregnancy was diagnosed using transrectal ultrasonography (5.0MHz linear array transducer, Aloka 500V, Corimetrics Medical Systems, Inc., Wallingford, CT) on d 47 of the breeding phase to confirm pregnancy to AI Final pregnancy rates were reported based on a 77d breeding phase for Yr1 and Yr2 (17d of AI and 60d of natural service), with final pregnancy diagnosis being performed on d 107, 30 d following the conclusion of breeding season Statistical Analysis A verage daily gain was calculated using two ADG calculation methods: 1) as the mean of the ADG of each period (or total ADG from d 0 to 140) divided by d on feed ( OADG); and 2) by regressing the BW against period and calculating the slope of the regression line (RADG) The resulting ADG values were compared using the PROC CORR procedure of SAS (SAS Inst Inc., Cary, NC.) to determine the correlation coefficients b etween the two calculations Developmental phase data including: ADG, BW, BCS, and BUN, in addition to temperament data were analyzed by analysis of variance for repeated measures using the PROC MIXED procedure of SAS (SAS Inst Inc., Cary, NC.) The f inal statistical model was:

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48 Yijkm = i + m + k + ik )mi + ()ikm + eijkm where: Yijkm = Animal performance characteristic (ADG, BW, BCS, or BUN) from ith treatment, of the jth pen, on the kth day (or period) from the mth year = overall mean i = fixed effect of ith treatment k = fixed effect of kth day (or period) m = random effect of year ik = treatment day (or period) interaction )mi = treatment year interaction ()ikm = treatment day (or period) year interaction eijkm = random error associated with measurement of the kth day (or period) on the jth pen, assigned to the ith treatment of the mth year The repeated measures statement included pen within year as the subject and were analyzed for d 0, 28, 56, 84, 112, and 140. Year was considered a rand om effect. All total DMI (total, supplement, and BGH) and nutrient intake (TDN and CP), percent of DMI of total BW and cost of gain, were analyzed using the PROC MIXED procedures of SAS (SAS Inst Inc., Cary, NC.) In addition, initial and final BW and BCS, and fertility data including age at puberty, weight at puberty, BCS at puberty, and days on treatment to puberty Fetal age and pregnancy rates within pen w ere analyzed using the same model Year and pen were considered random effects, with treatmen t and day being the main effect The statistical model was:

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49 Yij i k + eij where: Yij = Performance characteristic (intake, BW, BCS, fertility, or t emperament) from ith pen, assigned to the jth treatment = overall mean i = fixed effect of jth treatment k = random effect of year eij = random error associ ated with measurement of the ith pen, assigned to the jth treatment In all cases in which covariance analyses were utilized, autoregressive, toeplitz, unstructured, and compound symmetry covariance structures were assessed for best fit The autoregressive structure was revealed to be the best fit The procedure LIFETEST was used for s urvival analys e s on the age at puberty, days on t reatment to puberty, and fetal age with the resulting statistical model: S (t)= Pr(Tij>t) Where: S = the survival function T = random response variable of the ith heifer from the jth pen t = Time (d) until T is achieved Pr= probability that time of T is later then time t For all analysis, statistical differences were reported at P < 0.05, tendencies were identified at P = 0 .06 to P = 0.1 and interactions were reported to be statistically different at P < 0 1 with means being reported as LS means SE.

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50 Results and Discussion Feed Intake I ntake of BGH differed ( P < 0.01) among treatments with heifers in the CON treatment ( 3.5 0.37 kg.hd1.d1) consuming greater ( P < 0.05) quantities of BGH than CSBM ( 3.0 0.37 kg.hd 1.d 1 ) and PPH ( 2.6 0.37 kg.hd1.d1) treatments Similarly t otal TDN and CP intake from BGH differed ( P < 0.05) by treatment ; intake of TDN and CP for h eifers in the CON treatment (0.40 0.038 kg.hd1.d1; 0.09 0.016 kg.hd1.d1; fo r TDN and CP, respectively) was greater ( P < 0.05) than CSBM ( 0.35 0.038 kg.hd1.d1; 0.08 0.016 kg.hd1.d1), and PPH ( 0.30 0.038 kg.hd1.d1; 0.07 0.016 kg.hd1.d1) treatments The TDN and CP intake were also greater ( P < 0.05) for CSBM than PPH (Table 3 4). Within the two treatments receiving supplementation (CSBM and PPH), DMI of supplement during the development phase was greater ( P < 0.001) for heifers in the PPH treatment ( 2.8 0.18 kg.hd1.d1) than the CSBM treatment ( 1.2 0.18 kg.hd1.d1) Similarly, TDN ( 0.33 0.021 kg.hd1.d1 and 0.21 0.021 kg.hd1.d1for PPH and CSBM, respectively) and CP ( 0.08 0.008 kg.hd1.d1 and 0.05 0.008 kg.hd1.d1for PPH and CSBM, respectively) intake was greater ( P < 0.01) for heifers fed PPH than those fed CSBM Average t otal DMI during the development phase, including DMI from supplement and BGH was a ffected by treatment ( P < 0.0001; Table 3 4) Heifers in the C ON treatment, consuming only BGH, had the least total DMI ( 3.4 0.25 kg.hd1.d1), and consequently the least total TDN ( P < 0. 00 01; 0.39 0.024 kg.hd1.d1) and CP ( P < 0.0001; 0.09 0.017 kg.hd1.d1) intake This r educed DMI was likely associated wi th physical fill effect (Forbes, 1996), because diets exceeding an NDF content of 25%,

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51 such as the BGH, have been shown to decrease DMI (Allen, 2000) due to physical fill effect Since BGH was the sole source of nutrient intake for CON pens, its high NDF concentration possibly limited the rate of passage of feed from the rumen, causing a lengthened satiety signal and thereby limiting intake, a factor likely affecting not only the CON heifers, but all heifers because of their ad libitum access to BGH The N DF, ADF, TDN, and CP concentrations of the PPH used as supplement for t he PPH treatment (Table 3 2) were similar to previously reported values (Foster et al., 2009; Myer et al., 2009 ) Heifers in the PPH treatment pens consumed a total forage diet of BGH and PPH resulting in the greatest total DMI ( 5.3 0.25 kg.hd1.d1), total TDN ( P < 0.01; 0.63 0.024 kg.hd1.d1), and CP ( P < 0.0001; 0.14 0.017 kg.hd1.d1) intake. In addition, PPH heifers consumed the greatest daily DMI as a percentage of their B W ( P = 0.001; 2.0 0.07%) compared to CON (1.4 0.07%), and CSBM (1.6 0.0 7 % ) heifers Dry matter digestibility has an influence on ruminal physical fill by the physical presences of feedstuffs within the rumen and thus can regulate DMI Previous res earch showed a significant int eraction between forage type and DMI such that DMI was greater in legumes than grasses d ue to fragility of plant matter reducing retention time in the rumen (Waghorn et al., 1989; Oba and Allen, 1999) This decreased retenti on time is due to relative differences in digestibility with the legumes hay supplement having the structural fiber concentrations and morphological characteristic that that result in decreased NDF and ADF, consequently being more digestible (Foster et al ., 2009) The greater DMI of heifers supplemented with a legume (PPH) is supported by reports indicating increased DMI and organic matter digestibility when poor quality forages were supplemented with legumes in feeding scenarios ( Minson and

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52 Milford, 1967; Getachew et al., 1994; Foster et al., 2009) creating a synergistic associative effect This associative effect of feeding a 100% forage diet possibly modified the metabolic pr ocesses in the digestive tract, and created positive digestive interactions ( N iderkorn and Baumont, 2009; Niderkorn et al., 2011) such that the response of the heifer to a combination of forages differed from the response to the i ndividual forages. Heifers receiving the CSBM treatment had intermediate total DMI intake ( P < 0.01; 4. 3 0.25 kg.hd1.d1) resulting in intermediate total TDN ( 0.56 0.024 kg.hd1.d1) and CP intake ( 0.13 0.017 kg.hd1.d1) This could be explained through the hepatic oxidation theory, in which total body energetics work as an intake regulator Vola tile fatty acid profiles are strongly correlated to the type of feed being consumed (Allen, 2000) such that animals consuming a diet which will shift the acetate to propionate ratio in favor of propionate, typically a diet including nonstructural carbohy drates, tend to have reduced DMI (Illius and Jessop, 1996; Allen, 2000) Thus, with propionate being the primary precursor to gluconeogenesis in the liver, increased propionate absorp tion in the rumen likely increases insulin secretion ( Grovum, 1995), tri ggering satiety Another proposed explanation of HOT suggests receptors in the liver exist that are sensitive to propionate and have afferent fibers in the hepatic plexus (Anil and Forbes, 1980) Animal Growth and Performance For the two methods used t o calculate ADG Pearson correlation coefficient analyses revealed that both methods of ADG were highly correlated (r2=0.99; P < 0.0001) For all subsequent analyses the OADG calculation for ADG was used as the

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53 preferred method. No treatment period int eractions were detected for ADG, but treatment (Table 3 4) and period influenced ADG (Figure 3 3). T here was a tendency ( P = 0.06) for the CON treated heifers (0.18 0.11 kg.hd1.d1) to have lesser ADG than the PPH and CSBM which was likely a direct res ult of the reduced total DMI, TDN and CP intake during the dev elopmental phase. While the PPH treated heifers (0.46 0.11 kg.hd1.d1) had significantly greater total DMI, TDN, and CP intake, their ADG did not differ from the CSBM treated heifers (0.48 0.11 kg.hd1.d1), suggesting improved efficiency of nutrient utilization the CSBM heifers Typically the passage rate from the rumen increases in conjunction with increasing DMI, resulting in a decrease in ruminal propionate proportions ( Harrison et al ., 1975, 1976) Therefore, the greater DMI of the PPH pens, without resulting in greater ADG differing energy density of feeds In addition, this may be resulted in decreased ruminal propionate proportions and increased acetate: propionate ratios This d ecrease in propionate could result in a decrease in availability of gluconeogenic precursors within the liver (Allen, 2000) Ruminal fermentations ar e less efficient in most legumesupplemented diets compared to concentratesupplemented diets because gr eater dilution rates reduce total metabolic hydrogen recovery into VFA Thus, having the greater rat e of passage from the rumen of forage diet s can reduce the amount of ruminal digestion taking place and nutrient capture (Chalupa, 1977) The effect of per iod was noted when ADG declined from d 0 to 84 (d 0 to 28 = 0.43 0.11 kg.hd1.d1; d 28 to 56 = 0.20 0.11 kg.hd1.d1; d 56 to 84 = 0.17 0.11 kg.hd1.d1), peaking from d 84 to 112 (0.67 0.11 kg.hd1.d1) and being intermediate from d 112 to 140 ( 0 .38 0.11 kg.hd1.d1; Figure 3 3) The decline noted in the first 84

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54 d of the development phase could be attributed to decreased temperatures, causing increased maintenance requirements of the heifers due to cooler weather ( Baile and Della Fera, 1981; Y oung, 1983; Birkelo et al., 1991; Figure 3 9 ) In addition, supplementation amounts were not adjusted during the developmental phase. Thus, as heifers increased in BW, a greater proportion of their nutrient requirements were being met through the intake of BGH in the supplemented heifers Diets that are low in nutrient density and with reduced rate of digestion may result in decreased DMI, which could account for the decrease i n ADG for the final 28d period in all treatments There was no difference i n initial BW (d 0; P = 0.98) among treatments Mean BW throughout the development phase was not a ffected by treatment, however there was a treatment day interaction ( P = 0.06) for BW T he rate of increase of BW for the CON was at a lesser rate then the supplemented heifers T h e BW of CON from d 0 was 234 16.9 kg and on d 140 was 260 16.9 kg and when compared to the PPH (d 0 = 236 16.9 kg; d 140 = 300 16.9 kg), and the C SBM heifers (d 0 = 237 16.9 kg; d 140 = 303 16.9 kg; Figure 3 4) the CO N heifers gained at a slower rate. Final BW on d 140 was a ffected by treatment ( P = 0.05), with CON being lightest on d 140 (260 24.2 kg), and no differences observed between CSBM (303 24.2 kg) and PPH heifers (300 24.2 kg ; Table 3 4 ) Initial BCS (d 0) did not differ across treatments ( P = 0.85) Throughout the development phase there was no effect of treatment, day, or treatment day interaction on me a n BCS However, mean BCS on d 0 (5.2 0.13) tended ( P = 0.64) to be greater than BCS on d 56 (4.9 0.13), d 84 (5.0 0.13), d 112 (4.9 0.13), and d 140 (4.9 0.13; Figure 3 5) Final BCS (d 140) differed ( P = 0.003) with CON having the lesser

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55 BCS ( 4.6 0.15) than the supplement treatments, which did not differ (CSBM = 5.1 0.15; PPH = 5.2 0.15) The decrease in BCS i n the CON heifers is attributable to the differences in caloric intake and treatment day interaction in BW Concentrations of BUN were similar to those reported by Cooke et al (2008) for animals of a similar physiologic al status, and were w ithin the normal physiological range (Kaneko, 1989) The mean concentrations o f BUN for CON, CSBM and PPH were 21.02 mg/ d L, 21.68 mg/ d L, and 22.08 mg/ d L, respectively with no treatment day ( P = 0.966) treatment ( P = 0.669) or day ( P = 0.231) differences detected (Table 3 4) Optimal concentrations of BUN have been reported to be 11 to 15 mg/ d L in growing heifers (Byers and Moxon, 1980) indicating that these heifers consumed a diet exceeding CP requirements Strong linear rela tionships between BUN concentrations and rate of nitrogen excretion were reported in animals of several species (Kohn et al., 2005) The concentration of BUN was positively correlated between rumen degradable protein, level of ruminal ammonia and ruminal protein:energy ratio (Hammond, 1997) Typically feeding of forages, such as BGH, decreases the digestibility of t he protein, with reduced protein degradation in the rumen resulting in the absorption of nitrogen across the ruminal wall and into the blood stream (Kohn et al., 2005) However, w ith CSBM and PPH pens h aving increased CP intake and no difference in BUN concentrations, the effect of nutrient synchrony may have resulted in similar concentrations of BUN with N being incorporated into microbial protein, in contrast to being absorbed into the blood stream.

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56 Typically legumesupplemented cattle have increased ruminal NH3N concentrations because with most of the protein in legumes is in the form of soluble protein or rumendegradable protein (Broderi ck, 1995) However, because treatment and total CP intake did not alter concentrations of BUN all diet s may have supplied adequate energy and NH3N, resulting in improved microbial efficiency and protein syn thesis (Clark et al., 1992; Macr ae et al., 2006) In addition, increased N intake and improved digestion and retention were observed when perennial peanut hay was supplemented to lambs (Foster et al., 2009) This is in contrast to when grass hay diets that were supplemented with legumes, and did not meet the ruminant energy and N needs to optimize microbial synthesis (Mosi and Butterworth, 1985; Matizha et al., 1997) While the PPH heifers had the greatest total CP intake, with similar concentrations of BUN in this study could possibly be explained by the presence of condensed tannins (CT) in the PPH supplemented heifers Condensed tannins have the ability to react with supplemented plant proteins to form stable complexes and reduce their degradation in the rumen Condensed tannins have been shown to eliminate NH3N production at 3.5 h r of incubation during an in vitro study when legumes were fermented with grasses (Niderkorn et al., 2011) Thus, with a 3.82% concentration of CT on a DM basis previously reported in perennial peanut hay (Foste r et a l., 2009) While current samples of PPH were not analyzed for CT concentrations, their presences could have resulted in an increase in the N flowing from the rumen ( a result of decreased ruminal digestion; Aufrere et al., 2008) due to the associative effect of CT concentrations in the PPH treatment may have reduced the NH3N production in t he rumen. In addition, with the

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57 BUN concentration of the CSBM not differing from the CON heifers could be a result of a decrease in ruminal digestions in the CSBM heifers, due to increased rate of passage (Chalupa, 1977) Total cost of feed for the entire trial was $ 2 653.38 for CON, $4, 648.30 for CSBM, and $6, 605.75 for the PPH heifers To calculate cost of gain, the mean of the actual purchase price of feed and supplements for each year was used for each pen every year Purchase prices were as follows (all on an as fed basis) : PPH hay was valued at $242.61/tonne for Yr1 and Yr2, CSBM supplement was valued at $299.83/tonne for Yr1 and $390.21/tonne for Yr2, and BGH w as valued at $99.02/ tonne for Yr1 and Yr2, all on an as fed basis The cost of feed per head per day was different ( P < 0.001) for treatments with CON being the least ($0.48 0.021), CSBM being intermediate ($0.83 0.021), and PPH being greatest ($1.17 0.021) C ost of weight gain was $2.67 per kg gain for CON, $ 2.54 per kg gain for PPH, and $ 1.73 per kg gain for CSBM (Table 3 4) It can be noted that high quality square bales which had been housed under a barn were used for the perennial peanut hay In a practical beef cattle production scenario feeding of large round bales would reduce costs The reduced cost of weight gain for the CSBM heifers, with similar labor in this feeding scenario make it the most economically sound choice for beef cattle producers Fertility The mean age at puberty for CON ( 446 11.1 d), CSBM (423 11.1 d), and PPH (439 11.1 d; Table 3 5) was not a ffect ed by treatment ( P = 0.3 22 ) This agreed with survival analysis which indicated no differences in age of puberty ( P = 0. 167 ) Nutrition al management has an impact on the attainment of puberty, with heifers on a low plane of nutrition having delayed puberty (Day et al., 1986), particularly in breeds

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58 known to be later maturing (Berg and Walters, 1983) such as Bos indicu s crosses of cattle However, in this experiment, with no delay in puberty in the CON treatment compared to the supplemente d treatments (PPH and CSB M ), the plane of nutrition provided to the heifers may have been sufficient to prevent delaying the attainm ent of puberty In addition, feed efficiency may influence the attainment of puberty since heifers that ha d greater (less efficient) RFI values had decreased age at puberty (Shaffer et al., 2010) However, in the current study no differences between CSBM and PPH heifer ADG was detected, whereas heifers in the CSBM had lower total DMI, indicating that they may have been more efficient without altering age at puberty The days on treatment, or days f rom the initiation of the development phase, when supple mentation began, until heifers reached puberty, was no effect of treatment ( P = 0.4 24 ) on the mean age at attainment of puberty In addit ion, analysis of the distribution through survival analysis reported no difference ( P = 0. 140) among treatments The average interval to attainment of puberty was similar for CON ( 183 8.5 d ), CSBM ( 163 8.5 d ) and PPH ( 175 8.5 d ) heifers I t appears that heifers i n the CON treatment were receiving adequate energy to support the energy triggers on LH release requir ed for the attainment off puberty at a similar age as CSBM and PPH heifers (Rhodes et al., 1978; McCartor et al., 1979; Day et al., 1986) Weight is a primary factor a ffecting age of puberty (Joubert, 1963) The CON ( 292 12.2 kg), PPH ( 324 12.2 kg ), and CSBM ( 316 12.2 kg ) heifers did not differ in weight at puberty ( P = 0.164) despite the occurrence of differences in their ADG and DMI Mean BW of lactating, nonpregnant cows from within the herd is 585 kg (not including cows over 10 years of age or first calf heifers) It was suggested that heifers

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59 will reach puberty at 60% to 66% of their mature BW (Patterson et al., 1992) However, CON heifers reached puberty at 5 0% of their mature BW, CSBM at 54% and PPH at 55%, a possible result of time and rate of gain (Lynch et al., 1997) When heifers were fed to gain most of their weight in the final 90 d of the development phase, compared to heifers gaining at a steady rate, there was no effect of delayed ADG on age and weight at attainment of puberty (Clanton et al., 1983) This allows for heifers to be managed such that minimum feed inputs are used through the development phase, taking advantage of compensatory gains (Lalman et al., 1993) Th erefore with the tendency for differences in AD G that wer e noted during the development phase not existing during the breeding phase (Table 3 4) compensatory gain may have influenced CON heifers during the breeding phase. In addition, it has been reported that the preweaning growth phase exerts a larger effect on puberty in beef heifers than does the postweaning or developmental phase (Little et al., 1981; Clanton et al., 1983) This supports our current findings as all heifers, regardless of treatment, were managed together prior to weaning, with similar wean ing weights while differences in post weaning gains existed. In this study, there were no differences in BCS at puberty (Table 3 5) but previous reports indicate that there wa s a degree of fatness, or a b ody composition that must be achieved before pube rty may be attained in replacement heifers ( Grass et al., 1982; Nelson et al., 1982) however conflicting results exist as well ( Brooks et al., 1985) T hus, BCS may be correlated with puberty but may not be a primary factor causing the onset of puberty Yelich et al (1995) reported that the percentage of BW that was lipids at puberty was in dependent of ADG Thus with heifers in the CON having lesser

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60 ADG, they may have reached puberty at a different percentage of body fat than CSBM and PPH heifers. Ove rall pregnancy rate was derived from the pregnancy diagnosis 30 d following conclusion of the breeding phase. Overall pregnancy rates were no different ( P = 0.50) among treatments with 65 12.4% for CON, 77.5 12.4% for CSBM, and 87.5 12.4% for the PP H F etal age s was determined by ultrasonography and which were similar ( P = 0. 434 ) for CON ( 38 10.2 d ) CSBM ( 51.1 10.2 d ) and PPH ( 5 8 10.2 d ) treatments (Table 3 5) In addition, survival analysis indicated no differences in fetal age ( P = 0. 378 ) among treatments Thus, s ince heifers that become pregnant earlier in the breeding seaso n calve earlier, and tend to continue doing so throughout their production life, having increased kilograms of calves weaned throughout their lives (Lesmeister et al. 1973), treatment should not affect lifetime productivity of the heifers Results indicated no differences in production after first calf with no differences a mong treatment s from Yr1 for BW of cow ( P = 0.30), BCS of cow ( P = 0.49), and BW of calves ( P = 0.66) 95 d after initiation of the ir first calving se ason Combined production data from first calf heifers and fertility data from the study, suggests that there was no effect of treatment on the current reproductive performance of the heifers Temper ament In Yr2 when PS was assessed on d 84 and 140 with d ay tending ( P = 0.06) to influence PS (Figure 3 6) From mid point (d 84; 2.9 0.09) to the end of the development phase (d 140; 2.7 0.09), PS tended ( P = 0.06) to decline, indicating an improvem ent in temperament and reduced stress caused by cattle handling T reatment influenced PS ( P < 0.05) Heifers in the CSBM treatment (3.1 0.13) were more aggressive than CON (2.8 0.13) and PPH (2.5 0.13) heifers (Table 3 5 ) This can

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61 likely be attri buted to the random assignment of aggressive animals to the same pen within CSBM treatment, causing a high mean PS throughout the development phase Decreased growth rates ( Burrow and Dillon, 1997 ) and reduced feed conversion efficiency (Petherick et al., 2002) has previously established to be associated with more temperamental animals However, the CSBM heifers had the greatest PS, but their ADG did not differ from the PPH heifers, which had more docile PS. In assessment of EV and CS on d 0, 28, 56, 84, 112, and 140 there was no treatment day interaction or treatment effect for either variable; however EV ( P < 0.05; Figure 3 8) and CS ( P < 0.001; Figure 3 7) was influenced by day Heifers were handled in the same manor each time they were processed t hrough the cattle working facility Strong correlations to EV for feedlot behavior, barometric pressure, and ambient air temperatures changes from moderate to either high or low have been reported (Rittenhouse and Senft 1982; Hahn 1995), thus weather patt erns could be an explanation for the effect s of day on EV (Figure 3 9; 3 10; 3 11) From d 0 to d 140, CS decreased significantly (Figure 3 7) indicating acclimation to human handling and improved temperament over time. R esults reported in Braham crossb red cows indicated that exposure to human handling over time did not improve temperament (Cooke et al., 2009); however this is likely because the acclimation was less intense in the latter study, with only twice weekly visits to cows on pasture This is i n contrast to the current study when heifers were exposed to human interaction three mornings per week, and processed weekly through the cattle working facility Similarly, the acclimation of cattle to human interaction and handling reduced PS and CS, in dicating improvements in temperament ( Krohn et al., 2001) It is possible that age

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62 and physiological status a ffect the animals adaptations to human interaction. However, improvement in temperament could improve the reproductive performance of replacemen t heifers, as ill tempered animals have heightened secretion and circulating concentrations of ACTH and cortisol (Curley et al., 2008) Conclusion Successful development of replacement heifers is critical in the beef industry; however the opportunity cost of developing a heifer calf into a bred heifer can be substantial Thus, continuous research on new replacement heifer development strategies is essential This study revealed that temperament of heifers improved with handl ing and human interaction Body weight (BW) age, and body composition have all be en identified as benchmarks in the attainment of puberty However in this study there was no difference in the age, BW, and BCS at puberty existed despite differences in ADG, DMI, nutrition al intakes, and mean BW despite differing In addition, reproductive performance of the heifers was not affected by treatment T he supplementation of PPH provided gains similar to CSBM supplemented heifers, with no difference in reproductive performance, BW, ADG, and BCS indicating that PPH is an adequate feed option for replacement heifer development in the southeastern U.S.A However, CSBM supplementation appeared to be the most economically efficient supplement with lesser DMI, TDN, and CP intake s resulting in apparent lesser cost of weight gain wit h similar BW, ADG, and BCS, and no effect on fert ility While these cost analys e s may change over time with rising corn prices and in differ ing supplementation scenarios; this experiment reveals that PPH supplemented heifers had similar growth and reproductive performance when compared to CSBM supplemented heifers

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63 Figure 3 1 Schematic representing data collection for the development and breeding phase for heifers receiving different development diets 1 Devel opment phase development phase was initiated 140d prior to initiation of the breeding season (supplemental treatments were being applied). 2 Breeding phase 77 d breeding season following development phase (heifers were comingles with no treatments being applied) 3 Samples collected each d; BS blood sample, CS chute score, EV exit velocity, WT fasted body weight, BCS body condition score, and PS pen score; CS, PS, EV were only collect during Y r 2 (Year 2)

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64 Figure 3 2 Schematic of sp ecific breeding events during the breeding phase for heifers receiving different developmental diets 1 Injection of 25 mg of Prostaglandin 2 Non responders heifers that were not detected in estrus between d 0 to d 11 3 US transrectal ultras onography

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65 Figure 3 3 Mean ADG in kg by period for heifers receiving three different development diets a,b,c Means differ ( P < 0.05) .

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66 Fi gure 3 4 Mean BW by day for heif ers receiving three different developmental diets CON Control, CSBM 80% c orn 20% soybean meal supplement treatment, PPH perennial peanut hay supplement CSBM and PPH differ from CON on d 112 ( P < 0.05)

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67 Figure 3 5 Mean BCS (scale of 1 to 9, with 1 = em aciated and 9 = obese) by day for heif ers during the receiving three different developmental diets

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68 Figure 3 6 Mean pen score (average of 3 pen scores on a given date, on a 5 points scale with 1 being calm and 5 being aggressive) by day for heifers receiving three different development diets . a,b Means tend to dif fer (P = 0.06) Data collected in Year 2 only

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69 Figure 3 7 Mean chute score (on 5 point scale, with 1 being calm and 5 being aggressive) by day for heifers receiving three different development diets . Data collected in Year 2 only a,b,c,d,e Mea ns differ ( P < 0.05).

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70 Figure 3 8 Mean exit velocity (seconds for a heifer to travel 1.83 m after being releas ed from a squeeze chute) by day for heifers receiving three different development diets Data collected in Year 2 only a,b,c Means differ ( P < 0.05).

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71 Figure 3 9 Mean temperature from year 1 ( Yr1 ) and year 2 ( Yr2 ) by 28 d period during the development and breeding phase for heifers receiving three different development diets

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72 Figure 3 10. Mean relative humidity from year 1 ( Yr1 ) and ye ar 2 ( Yr2 ) by 28 d period during the development and breeding phase for heifers receiving three different development diets

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73 Figure 3 11. Mean r ainfall from year 1 ( Yr1 ) and year 2 ( Yr2 ) by 28 d period during the development and breeding phase for heifers receiving three different development diets

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74 Table 3 1 Nutritional values1 of feeds offered during the developmental phase2. Treatments 3 CSBM 3 PPH 3 BGH 4 Ingredient, DM Basis Yr15 Yr26 Yr1 Yr2 Yr1 Yr2 DM, % 92.7 93.6 90.7 91.3 91.1 92.1 TDN, % 83.5 84.0 61.0 60.0 56.5 58.0 CP, % 20.1 20.4 13.2 15.3 14.5 10.0 ADF, % 5.7 5.2 35.1 33.7 38.6 40.9 NDF, % 10.8 9.8 40.4 38.9 73.7 74.8 NEm (Mcal/kg) 1.52 1.53 1.28 1.27 1.06 1.09 NEg (Mcal/kg) 1.04 1.05 0.71 0.7 0. 50 0.54 1 Mean of two samples analyzed via Near Infrared Reflectance Analysis (NIR) 2 Development phase was initiated 140 d prior to initiation of the breeding season. 3 Heifers were assigned to one of three supplementation treatments: 1) heifers rec eived no supplementation with ad libitum access to bermudagrass hay (CON); 2) heifers received a corn/soybean supplement at 1.23 kg.hd-1.d-1 with ad libitum access to bermudagrass hay (CSBM); and 3) heifers received perennial peanut hay supplement at 2.74 kg.hd-1.d1with with ad libitum access to bermudagrass hay (PPH) 4 BGH bermudagrass hay nutritive values offered to all treatments during the development phase. 5 Yr1 Year 1 from Oct 2009 to March 2010 6 Yr2 Year 2 from Oct 2010 to March 2011

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75 Table 3 2 Chemical composition of the mineral supplements provided to developing heifers during the development phase1 and breeding phase2. CON & CSBM PPH Breeding Phase Component Min Max Min Max Min Max Calcium,% 14.00 16.80 12.00 14.40 16.0 19.0 Phosphorus, % 7.00 12.00 3.0 Salt, % 17.00 20.00 3.00 4.00 15.0 18.0 Magnesium, % 3.50 1.00 10.0 Potassium, % 1.00 1.00 Sulfur % 1.50 Zinc, PPM 2,500 6,600 2,800 Manganese, % 3,500 Copper, % 2 ,200 1,200 Cobalt, % 19.0 Iodine, PPM 4 60.0 90.0 68.0 Selenium, PPM 52.0 54.0 30.0 Vitamin A, IU 5 225,000 150,000 140,000 Vitamin D3, IU 25,000 15,500 45,000 Vitamin E, IU 200 150 1 Development phase was init iated 140 d prior to initiation of the breeding season. 2 Breeding phase all heifers were comingled, on grazing, receiving no dietary treatment. 3 Heifers were assigned to one of three supplementation treatments: 1) heifers received no supplementation w ith ad libitum access to bermudagrass hay (CON); 2) heifers received a corn/soybean supplement with ad libitum access to bermudagrass hay (CSBM); and 3) heifers received perennial peanut hay supplement with ad libitum access to bermudagrass hay (PPH)

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76 Table 3 3 Nutritional values of feed available to heifers during the breeding phase1. Ryegrass2 50/503 Ingredient, DM Basis Yr1 4 Yr2 5 DM, % 89.6 92.1 90.5 TDN, % 67.0 65.5 80.0 NEm Mcal/kg of DM 1.48 1.44 1.3 NEg, Mcal/kg of DM 0.89 0.86 1.94 Crude protein, % 20.2 24.8 18.0 ADF, % 30.4 27.7 25.35 NDF, % 50.7 44.7 51.45 1 Breeding phase was initiated after a 140 d development phase for 77 d. 2 Ryegrass pasture ( Lolium perenne L.) grazing 3 Mixture of 50% corn gluten feed and 50% soybean hul ls, values based on of NRC (2000) fed at 1.81 kg.hd-1.d-1 4 Yr1 Year 1 from Oct 2009 to March 2010 5 Yr2 Year 2 from Oct 2010 to March 2011

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77 Table 3 4 DMI parameters of heifers during the development phase1 and growth parameters. Treatments 2 Item CON CSBM PPH SE P value Intake Total DMI, % BW 1.4 a 1.6 b 2.0 c 0.07 0.0003 Total DMI, kg.hd 1 .d 1 3.4 4.3 b 5.3 c 0.25 <0.0001 Total TDN intake 3 kg.hd 1 .d 1 0.39 a 0.56 b 0.63 c 0.024 <0.0001 Total CP intake, kg.hd 1 .d 1 0.09 a 0.13 b 0.14 c 0. 017 <0.0001 Total supplementation DM intake, kg.hd -1 .d -1 1.2a 2.8b 0.183 0.0001 Total supplementation TDN intake, kg.hd -1 .d -1 0.21a 0.33b 0.021 0.0004 Total supplementation CP intake, kg.hd -1 .d -1 0.05a 0.08b 0.008 0.0023 Total bermuda grass hay D MI, kg.hd -1 .d -1 3.5c 3.0b 2.6a 0.372 0.0014 Total bermuda grass hay TDN intake, kg.hd -1 .d -1 0.40c 0.35b 0.30a 0.038 0.0014 Total bermuda grass hay CP intake, kg.hd -1 .d -1 0.09c 0.08b 0.07a 0.016 0.0025 Animal performance ADG during development phas e, kg 0.18a 0.48b 0.46b 0.109 0.069 ADG during breeding phase 4 kg 0.72 0.64 0.85 0.084 0.209 Initial BW 5 kg 234 237 236 11.4 0.975 Final BW 5 kg 260 a 303 b 300 b 24.21 0.024 Mean BW 6 245 268 266 16.34 0.370 Initial BCS 7 5.2 5.3 5.3 0.285 0.850 Final BCS 7 4.6 a 5.1 b 5.2 b 0.145 0.003 Mean BCS 8 4.8 5.2 5.2 0.13 0.126 BUN 9 mg/dL 21.0 21.7 22.1 0.89 0.669 Feed cost of weight gain 1 0 $/kg gain 2.67 1.73 2.54 1 Development phase 140 d supplementation period 2 Heifers were assigned to one of three supplementation treatments: 1) heifers received no supplementation with ad libitum access to b ermudagrass hay (CON); 2) heifers received a corn/soybean supplement at 1.23 kg.hd-1.d-1 with ad libitum access to b ermudagrass hay (CSBM); and 3) heifers receiv ed perennial peanut hay supplement at 2.74 kg.hd-1.d1with with ad libitum access to b ermudagrass hay (PPH) 3 Intake is defined as the total disappearance of feed (offered feedorts) 4 ADG during breeding season ADG of the 84 d breeding phase followi ng the development phase. 5 Initial and Final BW Mean body weight of heifers on d 0 and d 140 of development phase. 6 Mean BW Mean body weight as determined by repeated measures 7 Initial and Final BCS body condition score on d 0 and d 140 of development phase. 8 Mean BCS Mean body condition score as determined by repeated measures 9 BUN Blood Urea Nitrogen as an average of all 28 d values 10 Feed cost of weight gain calculated based off feed cost of individual treatment on a hd/d basis as a function of ADG a,b,c Means differ ( P < 0.05)

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78 Table 3 5 Tem perament data (Year 2 only) during the development phase1 and fertility data Treatments 2 CON CSBM PPH SE P value Temperament Pen Score3 2.8ab 3.1b 2.5a 0.13 0.026 Chute Score4 2.4 2.4 2.4 0.06 0.982 Exit Velocity5 0.67 0.67 0.77 0.038 0.117 Fertility Age at attainment of puberty, d6 446 423 439 11.1 0.322 WT at attainment of puberty, kg 7 291 316 324 12.2 0.164 BCS at attainment of puberty8 5.0 5.2 5.2 0.15 0 .265 D on treatment to until attainment of puberty, d 9 183 163 175 8.5 0.424 Fetal age, d10 38 51 58 10.2 0.434 Overall pregnancy rate, %11 65 78 88 12.4 0.500 1 Development phase 140 d supplementation period for both year 1 and year 2 2 Heifers were assigned to one of three supplementation treatments: 1) heifers received no supplementation with ad libitum access to bermudagrass hay (CON); 2) heifers received a corn/soybean supplement at 1.23 kg.hd-1.d-1 with ad libitum access to b ermudagrass hay (C SBM); and 3) heifers received perennial peanut hay supplement at 2.74 kg.hd-1.d1with with ad libitum access to bermudagrass hay (PPH) 3 Pen Score based on a 1 to 5 scale, with 1 being docile and 5 being aggressive (only year 2). 4 Chute Score based on a 1 to 5 scale, with 1 being docile and 5 being aggressive (only year 2). 5 Exit velocity measure of seconds taken for animal to travel 1.83 m from squeeze chute (only year 2) 6 Age at attainment of puberty the age of the week in which the first ri se of P4 was detected. 7 BW at attainment of puberty BW prior to P4 Rise + [ADG of Period of Rise (Date of P4 Rise Date of Prior 28 d BW day)]. 8 BCS at attainment of puberty body condition score from the period the rise of P4 was detected. 9 Days on treatment until attainment of puberty days from the start of the 140 d development phase until puberty. 10 Fetal age estimated age of fetus at pregnancy diagnosis 30 following sire removal. 11 Overall pregnancy rate total heifers pregnant 30d followi ng bull removal. a,b,c Means differ ( P < 0.05).

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79 LIST OF REFERENCES Adams, G P ., R L Matteri, J P Kastelic, J C Ko, and O J Ginther 1992. Association between surges of follicle stimulating hormone and the emergence of follicular waves in heifer s. J. Reprod. Fertil 94:177 188. Albaugh, R a nd H. T Strong 1972 Breeding yearling beef heifers California Agr Exp Sta Circ 433. Allen, M 2000. Effects of d iet on short t erm r egulatin of f eed i ntake by l actating d airy cattle J Dairy Sci. 83( S uppl. 7):1598 624 Allen, M S 1996 Physical constraints on voluntary intake of forages by ruminants J. Anim Sci 74:3063 3075 Allen, M S., andB. J. Bradford, and M. Oba. 2009. BOARD INVITED REVIEW: The hepatic oxidation theory of the control of feed intake and its application to ruminants J. Anim. Sci. 87: 3317 3334. Amstalden, M., M R Garcia, S W Williams, R. L Stanko, S E Nizielski, C. D Morrison, D H Keisler, and G L Williams 2000. Leptin gene expression, circulating leptin, and lut einizing hormone pulsatility are acutely responsive to short term fasting in prebubertal heifers: Relationships to circulating insulin and insulin like growth factor I Biol. Reprod. 63:127 133. Anderson, K J., D G LeFever, J S Brinks, and K G Odde 1991. The use of reproductive tract scoring in beef heifers Agri Practice 12:19 26. Anil, M H., and J M Forbes 1980. Feeding in sheep during intraportal infusions of short chain fatty acids and the effect of liver denervation. J Physiol 298:407 414. Arije, G F. and J N Wiltbank 1971 Age and weight at puberty in Hereford heifers. J. Anim. Sci.33:401 406. Arije, G F., and J N Wiltbank 1975 Prediction of Age and Weight at Puberty in Beef Heifer s. J. Anim. Sci. 38: 803 810. Arthington, J D., X Qiu, R F Cooke, J M B Vendramini, D B Araujo, C C Chase Jr., and S W Coleman. 2008 Effects of preshipping management on measures of stress and performance of beef steers during feedlot receiving J. Anim Sci 86:2016 2023. Arthur, P F., J A Archer, R M Herd, and G J. Melville 2001 Response to selection for net feed intake in beef cattle. Proc Of Assoc Advmt Anim Breed Genet 14:135 138.

PAGE 80

80 Aufrere, J., M Dudilieu, and C. Poncet 2008 In vivo and in situ measurements of the digest ive characteristics of sainfoin in comparison with lucerne fed to sheep as fresh forages at two growth stages and as hay Animal 2:1331 1339. Baile, C. A., and M A Della Fera 1981. Nature of hunger and satiety control system in ruminants J Dairy Sci. 64:1140 1152. Baker, J F., C R Long, G A Posada, W H McElhenney, and T C Cartwright 1989. Comparison of cattle of a fivebreed diallel: Size, growth, condition and pubertal characters of second generation heifers J Anim Sci 67:1218 1229 Bassett, J M., R H Weston, and J P Hogan. 1971. Dietary regulation of plasma insulin and growth hormone concentration in sheep. Aust J. Biol. Sci 24:321 330. Bauchop, T., and S R Elsden 1960 The growth of microorganisms in relation to their energy s upply J. Gen Microbiol 23:457 469. Beaty, J L., R C Cochran, B A Lintzenich, E S Vanzant, J L Morrill, R T Brandt Jr, and D E Johnson. 1994. Effect of frequency of supplementation and protein concentration in supplements on performance and digestion characteristics of beef cattle consuming low quality forages J. Anim Sci 72:2475 2486 Berg, R T., and L E Walters 1983. The meat animal: Changes and chal lenges. J. Anim. Sci. 57( Suppl. 21):133 146 Berthoud, H R., and W L Neuhuber 2 000 Functional and chemical anatomy of the afferent vagal system Auton Neurosci 85:1 17. Birkelo, C. P., D E Johnson, and H P Phetteplace 1991. Maintenance requirements of beef cattle as affected by season on different planes of nutrition. J. Anim Sci 69:1214 1222. Blaxter, K. 1980. Discussion paper: use of energy for maintenance and growth. In: Energy Metabolism, Proceedings of the 8th Symposium on En ergy Metabolism. Mount, L. E. Pages 183 188. Butterworths, London, UK. Blaxter, K L., and F W Wainman 1964 Utilization of energy of different rations by sheep and cattle for maintenance and for fattening J. Agric Sci 63:113 128. Bloomfield, F H., M H Oliver, C. D Giannoulias, P D Gluckman, J E Harding, and J R Challis 2003. Brief u ndernutrition in lategestation sheep programs the hypothalamic pituitary adrenal axis in adult offspring Endocrinology 144:2933 2940.

PAGE 81

81 Bohnert, D W., C S Schauer, and T DelCurto 2002. Influence of rumen protein degradability and supplementation frequency on performance and nitrogen use in ruminants consuming low quality forage: Cow performance and efficiency of nitrogen use in wethers J. Anim Sci 80:1629 1637. Bohnert, D W., C S Schauer, M L Bauer, and T DelCurto 2002. Influence of rumen p rotein degradability and supplementation frequency on steers consuming low quality fo rage: Site of digestion and microbial efficiency J. Anim Sci 80:2967 2977. Brinks, J. S. 1994. Genetic influences on reproductive performance of twoyear old beef femal es. Factors Affecting Calf Crop. Pages 45 53. M. J. Fields and R. J. Sand, ed. CRC Press, Boca Raton, FL. Broderick, G A 1995. Desirable characteristics of forage legumes for improving protein utilization in ruminants J. Anim Sci 73:2760 2773. Bronson, F H. and J M Manning 1991 The energetic regulation of ovulation: A realistic role for body fat Biol. of Reprod 44 : 945 950. Brooks, A L., R E Morrow, and R S Youngquist 1985. Body composition of beef heifers at puberty Theriogenology 24:235 250. Brown, J E., C J. Brown, and W T Butts 1972. Relationships among weights, gains and earliness of maturing in Hereford and Angus females J. Anim. Sci. 35:507 517. Bryant, M P. and L. M Robinson. 1962. Some nutritional characteristics of predo minant culturable ruminal bacteria. J. Bact 84:605 614. Buckley, B A., J F Baker, G E Dickerson, and T G Jenkins. 1990 Body composition and tissue distribution from birth to 14 months for three biological types of beef heifers J. Anim Sci 68:31 09 3123. Bunting, L.D., J.A. Boling, and C T MacKown. 1989. Effect of d ietary p ro tein l evel on n itrogen m etabolism in the g rowing bovine: N itrogen r ecycling and i ntestinal p rotein s upply in calves J. Anim. Sci. 67:810 819 Burroughs, W., P Gerlaugh, B H Edgington, and R M Bethke. 1949 The influence of corn starch upon roughage digestion in cattle J. Anim. Sci 8:271 278. Burrow, H M., and R D Dillon 1997. Relationships between temperament and growth in a feedlot and commercial carcass traits o f Bos indicus crossbreds. Aust J. Exp Agric 37:407 411. Bushmich, S L., R D Randel, M M McCartor, and L. H Carroll 1980. Effect of dietary monensin on ovarian response following gonadotropin treatment in prepuberal heifers. J. Anim. Sci. 51: 692 6 97.

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82 Byerley, D J., J G Berardinelli, R. B Staigmiller, and R E Short 1987. Progesterone concentrations in beef heifers bred at puberty or third estrus J. Anim Sci 65:1571 1575 Byers, F M., and A L Moxon. 1980. Protein and selenium levels for growing and finishing bee f cattle. J. Anim. Sci. 50:1136 1144. Carstens, G E., D E Johnson, M A Ellenberger, and J D Tatum 1991. Physical and chemical components of the empty body during compensatory growth in beef steers J. Anim Sci 69:3251 3264 Caton, J S., and D V Dhuyvetter 1997 Influence of energy supplementation on grazing ruminants: requirements and responses J. Anim Sci 75:533 542. Chalupa, W 1977 Manipulating rumen fer mentation. J. Anim. Sci. 45:585 599. Church, D. C. 1979. Di gestive physiology and nutrition of ruminants. Vol. 1. Digestive Physiology 2nd Ed O&B Books, Corvallis, OR. Church, D. C. 1988. The Ruminant Animal: Digestive Physiology and Nutrition. Pages 77 85. 1st Ed D. C. Church, ed. Prentice Hall, Englewood Clif fs, NJ. Church, D C. and A Santo, 1981. Effect of graded levels of soybean meal and of nonprotein nitrogenmolasses supplement on consumption and digestibility of wheat straw J. Anita Sci 53:1609 1615. Clanton, D C., L E Jones, and M E England 1983 Effect of rate and time of gain after weaning on the development of replacement beef heifers J. Anim Sci 56:280 285. Clark, J H., T H Klusmeyer, and M R Cameron 1992. Microbial protein synthesis and flows of nitrogen fractions to the duodenu m of da iry cows. J. Dairy Sci. 75:2304 2323. Clark, R. T., K W Creighton, H H Patt erson, and T. N. Barrett. 2005. Economic and tax implications for managing beef r eplacement h eifers Prf Anim Sci 21:164 173. Clarke, I J., R J. E Horton, and B W Doughton 1990 Investigation of the mechanism by which insulininduced hypoglycemia decreases luteinizing hormone secretion in ovariectomized ewes Endocrinology 127:1470 1476. Clifford, A J. and A D Tillman 1968. Urea and isolated soy protein in s heep purified diets J. Anim Sci 27:485 489 Coleman, S W. and R D Wyatt 1982. Cottonseed meal or small grains forage as protein supplements fed at different intervals J. Anita Sci 55:11 17

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83 Cooke R F., J D Arthington, D B Araujo, G C Lamb, and A D Ealy 2008. Effects of supplementation frequency on performance, reproductive, and metabolic responses of Brahmancrossbred females. J. Anim. Sci. 86:2296 2307. Cooke, R F., J D Arthington, C R Staples, and X Qiu 2007 Effects of supplem ent type and feeding frequency on performance and physiological responses of yearling Brahmancrossbred steers. Prof. Anim. Sci. 23:476 481. Cooke, R F., J D Arthington, D B Araujo, and G C Lamb 2009. Effects of acclimation to human interaction on performance, temperament, physiological responses, and pregnancy rates of Brahmancrossb red cows. J. Anim. Sci. 87:4125 4132. Corah, L R., T G Dunn, and C C Kalthenbach. 1975. Influence of prepartum nutrition on the reproductive performance of beef fe males and the performance of their progeny. J. Anim. Sci. 41:819 824. Cotta, M A. and J B Russell. 1982. Effect of peptides and amino acids on efficiency of rumen bacterial protein synthesis in continuous culture. J Dairy Sci. 65:226 234 Cundiff, L. V K E Gregory, R M Koch, and G E Dickerson 1986 Genetic diversity among cattle breeds and use to increase beef production efficiency in a temperate environment Proc 3rd World Congr on Genet Appl to Livest Prod IX Pages 271 282 Lincoln, NE. Curley, K O Jr., D A Neuendorff, A W Lewis, J J. Cleere, T H Welsh Jr., and R D Randel 2008. Functional characteristics of the bovine hypothalamic pituitary adrenal axis vary with temperament. Horm. Behav. 53:20 27. Currier, T A., D W Bo hnert, S J. Falck, and S J Bartle 2004 a. Daily and alternate day supplementation of urea or biuret to ruminants consuming low quality forage: I Effects on cow performance and the efficiency of nitrogen use in wethers. J. Anim. Sci. 82:1508 1517. Curri e r, T. A., D. W. Bohnert, S. J. Falck, C S Schauer, and S J. Bartle 2004b. Daily and alternateday supplementation of urea or biuret to ruminants consuming low quality forage: III Effects on ruminal fermentation characteristics in steers J. Anim. S ci. 82: 1528 1535 Day, M L., K Imakawa, D D Zalesky, R J. Kittok, and J E Kinder 1986. Effects of restriction of dietary energy intake during the prepubertal period on secretion of luteinizing hormone and responsiveness of the pituitary to luteini zing hormonereleasing hormone in heifers J. Anim Sci 62:1641 1648 Day, M L., K Imakawa, M Garcia Winder, D D Zalesky, B D Schanbacher, R J. Kittok, and J E Kinder 1984. Endocrine mechanisms of puberty in heifers: estradiol negative feedback regulation of luteinizing hormone secretion. Biol. of Reprod. 31( Suppl. 2):332 341.

PAGE 84

84 Day, M L., K Imakawa, P L Wolfe, R J Kittok, and J E Kinder 1987. Endocrine mechanisms of puberty in heifers Role of hypothalamopituitary estradiol receptors in the negative feedback of estradiol on luteinizing hormone secretion. Biol. of Reprod 37( Suppl. 5) : 1054 1065. Delavaud, C., F Bocquier, Y Chilliard, D. H Keisler, A Gertler, and G Kann 2000. Plasma leptin determination in ruminants: Effect of nutri tional status and body fatness on plasma leptin concentration assessed by a specific RIA i n sheep. J. Endocrinol. 165:519 526. Dow, J. S., J. D. Moore Jr C.M. Bailey, and W.D. Foote. 1982. Onset of p ubert y in h eife rs of diverse beef breeds and c rosses J Anim Sci. 55: 1041 1047. Duble, R L., J A Lancaster, and E C Holt 1971. Forage characteristics limiting animal performance on warm season perennial grasses. Agron. J. 63:795 798. Egan, A R 1980 Host animal rumen relationships Proc Nutr Soc 39:79 87 Ehrhardt, R A., R M Slepetis, J Siegal Willott, M E Van Amburgh, A W Bell, and Y R Boisclair 2000. Development of a specific radioimmunoassay to measure physiological changes of circulating leptin in cattle and sheep. J. Endo. 166:519 528. Evans A C O G. P Adams, and N C Rawlings 1994. Endocrine and ovarian fo llicular changes leading up to the first ovulation in prepubertal heif ers. J. Reprod. Fertil. 100:187 194. Evans, A C O 2003 Characteristics of ovarian follicle develop ment in domestic ani mals. Reprod. Domest. Anim. 38: 1 7. Farmer, C G., R C Cochran, T G Nagaraja, E C Titgemeyer, D E Johnson, and T A Wickersham 2004 Ruminal and host adaptations to changes in frequency of protein supplementation. J. Anim. Sci 82:895 903. Ferrell, C L., and J W Oltjen 2008. ASAS CENTENNIAL PAPER : Net energy systems for beef cattle Concepts, application, and future models J Anim Sci 86: 2779 2794. Ferrell, C L., J L Koong, and J A Nienaber 1986. Effect of previous nutrition on body composition and maintenance energy cost of gro wing lambs. Br. J. Nutr. 56:595 605. Flatt, W. P., P. W. Moe, R. R. Oltjen, P. A. Putnam and N. W. Hooven. 1967. Fourth Symposium on Energy Metabolism. Jablonna, Poland. Forbes, J M 1996. Integration of regulatory signals controlling forage intake in ruminants J Anim Sci 74: 3029 3035.

PAGE 85

85 Forbes, J M 2000. Physiological and metabolic aspects of feed intake control. Farm Animal Metabolism and Nutrition. Pages 319 332 J. P F DMello, ed CAB Intl Publ., Wallingford, UK. Forbes, J M 2007. A personal view of how ruminate animals control their intake and choice of food: minimal total discomfort Nutr ition Research Reviews. 20:132 146. Fortune, J E 1994 Ovarian follicular growth and development in mammals Biol. Reprod. 50:225 232. Foster, J. L., A. T. Adesogan, J. N. Carter, A. R. Blount, R. O. Myer, and S. C. Phatak. Intake, digestibility, and nitrogen retention by sheep supplemented with warm season legume hays or soybean meal. J. A nim Sci. 87:2891 2898. French, E. C., G. M. Prine and A. R. Blount. 2006. Perennial Peanut: An Alternative Forage of Growing Importance. University of Florida, Gainesville, FL. IFAS Extension SS AGR 39. Friedman, M I., and M G Tordoff 1986. Fatty aci d oxidation and glucose utilization interact to control food intake i n rats. Am. J. Physiol. 51:R840 R845. Friedman, M I., M G Tordoff, and I Ramirez 1986. Integrated metabolic control of food intake. Brain Res. Bull. 17:855 859. Funston, R N and G H Deutscher 2004 Comparison of target breeding weight and breeding date for replacement beef heifers and effects on subsequent reproduction and calf performance. J. Anim Sci. 82: 3094 3099 Gallup, W D. and H M Briggs 1948. The apparent digestibility of prairie hay of variable protein content with some observation of fecal nitrogen excretion by steers in relation to their dry matter intake. J Anim Sci 7:110 116. Galyean, M L 1999 Review: Restricted and programmed feeding of beef cattle Defi nitions, application, and research results. Prof. Anim. Sci. 15:1 6. Garrett, W N 1979. Relationships among diet, metabolizable energy utilization and net energy values of feedstuffs. J. Anim. Sci. 49:1402 1409. Gasser, C L., D E Grum, M L Mussard, F.L Fluharty, J E Kinder, and M L Day 2006. Induction of precocious puberty in heifers I: Enhanced secretion of luteinizing hormone. J. Anim. Sci. 84: 2035 2041. Getachew, G., A N Said, and F Sundstol 1994. The effect of forage legume supplementa tion on digestibility and body weight gain by sheep fed a basal diet of maize stover Anim. Feed Sci. Technol. 46:97 108.

PAGE 86

86 Ginther O J., J P Kastelic and L Knopf 1989. Composition and characteristics of follicular waves during the bovine estro us cycle. Anim. Reprod. Sci. 20: 187 200. Graham, N., and T W Searle. 1972. Balances of energy and matter in growing sheep at several ages, body weights, and planes of nutrit ion. Aust. J. Agric. Res. 23:97 108. Grass, J. A., P J. Hansen, J J. Rutledge, and E R Hauser 1982. Genotype x environmental interactions on reproductive traits of bovine females I Age at puberty as influenced by breed, breed of sire, dietary regimen and season. J. Anim Sci 55:1441 1457. Gray, R., and K. J. McCracken. 1979. Plane of nutrition and the maintenance requirement. Pages 163 165. Energy Metabolism of Farm Animals. EAAP Publ. No. 26, Cambridge, England. Grovum, W L 1986. A new look at whats controlling food intake. In: F N Owens (Ed.) Feed Intake by Beef Cattle. Pages 1 121 Okla Agric Exp Sta MP Stillwater OK Grovum, W L 1995. Mechanisms explaining the effects of short chain fatty acids on feed intake in ruminants osmotic pressure, insulin and glucagon. Ruminant Physiology: Digestion, Metabolism, Growth and Reproduction. Pages 173 197 W V Englehardt, S LeonhardMarek, G Breves, D.Geisecke, ed. Ferdinand Enke Verlag, Stuttgart, Germany. Guthrie, M J. and D G Wagner 1988 I nfluence of protein or grain supplementation and increasing levels of soybean meal on intake, utilization and passage rate of prairie hay in beef steers and heifers J. Anim. Sci. 66: 1529 1537. Hahn, G L 1995 Environmental influences on feed intake and perf ormance of feedlot cattle. Pages 207 225 Intake by feedlot cattle: Proceedings of the Symposium Oklahoma State University, Stillwater, OK. Hall, J B., R B Staigmiller, R. A Bellows, R. E Short, W M Moseley, and S E Bellows 1995 Body composition and metabolic profiles associated with puberty in beef heifers J. Anim. S ci. 73: 3409 3420. Hammond, A C 1997 Update on BUN and MUN as a guide for protein supplementation in cattle. Pages 43 52. Proc Florida Ruminant Nutr Symp., Univ ersity of Florida, Gainesville FL Hammond. J. M., C J. Hsu, I S Mondeschein, and S F Caurung 1988. Paracrine and autocrine functions of growth factors in the ovarian follicle. J Anim Sci 66( Suppl. 2):21 31 Hansel, W 1959. The estrous cycle of the cow H H Cole and P T Cupps (Ed.) Reproduction. Vol I Acad Press, New York and London.

PAGE 87

87 Hardin, D R., and R D Randel 1983. Effect of monensin on postpartum interval to first estrus and serum LH response to 0, 1, 2, or 4 mg estradiol 17b at 21 days postpartum Theriogenology 19:343 354 Harmeyer, J., and H Martens 1980. Aspects of urea metabolism in ruminants with reference to the goat J. Dairy Sci. 63:1707 1728. Harrison, D G., D E Beever, D J. Thomson, and D F Osbourn. 1975. Manipulation of rumen fermentation in sheep by increasing the rate of flow of water from the ru men. J. Agric. Sci. Camb. 85:93 101. Harrison, D G., D E Beever, D J. Thomson, and D F Osbourn. 1976. Manipulation of fermentation in the ru men. J. Sci. Food Agric. 27:617 620. Hennessy, D W., P J. Willlamson, J V Nolan, T J. Kempton, and R A Leng 1983 The roles of energy or proteinrich supplements in the subtropics of young cattle consuming basal diets that are low in digestible energy and protein. J Agric Sci Camb 100:657 666 Hileman, S M., K K Schillo, and J B Hall. 1993. Effects o f acute, intra cerebroventricular administration of insulin on serum concentrations of luteinizing hormone, insulin and glucose in ovariectomized lambs during restricted and ad libitum feed intake. Biol Reprod. 48:117 124. Hileman, S M., K K Schillo, J M Kearnan, J B Hall, and S Mohapatra. 1991. Effects of metabolic fuel restriction on patterns of LH and GH in ovariectomized lambs Annu Mtg of the Society for the Study of Reproduction. ( Abstr. ) 138. Hill, G M. 2002. Peanut by products fed to catt le Vet Clin Food Anim 18:1355 1360. Hogan, J P 1975 Symposium: Protein and amino acid nutrition in the high producing cow Quantitative aspects of nitrogen utilization in ruminants J Dairy Sci. 58:1164 1177. Holm, D. E., P N Thompson, and P C I rons 2009. The value of reproductive tract scoring as a predictor of fertility and production outcomes in beef heifers J. Anim. Sci. 87: 1934 1940 Hopper, H W., S E Williams, D. J Byerley, M M Rollosson, P O Ahmed, and T E Kiser 1993. Effect of prepubertal body weight gain and breed on carcass composition at puberty in beef heifers J Anim Sci 71: 1104 1111. Hume, I D. and P R Bird 1970. Synthesis of microbial protein in the rumen. IV The influence of the level and form of dietary sul phur Australian J Agr Res 21:315 322. Huntington, G B 1997. St arch utilization by ruminants: F rom basics to the bunk J. Anim. Sci. 75: 852 867.

PAGE 88

88 Illius, A W., and N S Jessop 1996. Metabolic constraints on voluntary intake in ruminants J Anim S ci 74:3052 3062. Imakawa, K M., M L Day, M Garcia Winder, D D Zalesky, R J. Kittok, B D Schanbacher, and J E Kinder 1986 Endocrine changes during restoration of estrous cycles following induction of anestrus by restricted nutrient intake in b eef heifers J. Anim Sci 63:565 571 Inui, A 2001 Ghrelin: An orexigenic and somatotrophic signal from the stomach. Nature Rev. Neurosci. 2:551 560. Ireland, J J. 1987. Control of follicular growth and development. J. of Repro. and Fertility Suppl. 3 4: 39 54. Ireland, J J. and J F Roche. 1983. Growth and differentiation of large antral follicles after spontaneous luteolysis in heifers: changes in concentration of hormones in follicular fluid and specific binding of gonadotropins to follicles J of Anim Sci 57:157 167 Ireland, J J. and J F Roche. 1987. Hypotheses regarding development of dominant follicles during a bovine estrous cycle. In Follicular Growth and .Ovulation Rate in Farm Animals Pages 1 18 Eds JF Roche and D O'Callaghan. Martin us Nijhoff Publishers, Dordrecht Netherlands. Ireland, J J., M Mihm, E Austin, M G Diskin, and J F Roche 2000. Historical perspective of turnover of dominant follicles during the bovine estrous cycle: key concepts, studies, advancements, and term s. J. Dairy Sci. 83:1648 1658. Johnson, C R., B A Reiling, P Mislevy, and M B Hall 2001. Effects of nitrogen fertilization and harvest date on yield, digestibility, fiber, and protein fractions of tropical grasses J. Anim Sci. 79:2439 2448. Jones, E J., J D Armstrong, and R W Harvey 1991 Changes in metabolites, metabolic hormones, and luteinizing hormone before puberty in Angus, Braford, Charolais, and Simmental heifers J. Anim Sci 69:1607 1615 Joubert, D M 1963. Puberty in fem ale fa rm animals. Anim. Breed. 31:295 (Abstr.). Kaneko, J J. 1989 Clinical Biochemistry of Domestic Animals (4th Ed.) Pages 886 891. Academic Press, San Diego, CA. Kato J., Y Atsumi, M Inaba, 1974 Estradiol receptors in female rat hypothalamus in the devel opmental stages and during pubescence. Endocrinology 94:309 317. Keele, J W., C B Williams, and G L Bennett 1992. A computer model to predict the effects of level of nutrition on composition of empty body gain in beef cattle: I Theory and development J. Anim Sci 70:841 857

PAGE 89

89 Keisler, D. H., J A Daniel, and C D Morrison 1999 The role of leptin in nutritional status and reproductive function J. Reprod. Fertil. Suppl. 54:425 435. Kempster, A J., A Cuthbertson, and G Harrington. 1976. Fat dis tribution in steer carcasses of different breeds and crosses distribution between depots Anim Prod 23:223 232 Kennedy, P M 1980. The effects of dietary sucrose and the concentration of plasma urea and rumen ammonia on the degradation of urea in the g astrointestinal tract of cattle Br J. Nutr 43:125 140 Knopf, L., J P Kastelic, E Schallenberger and O. J. Ginther 1989. Ovarian follicular dynamics in heifers: test of twowave hypothesis by ultrasonically monitoring individual follicles Domestic Anim Endo 6:111 119. Kohn, R A, M M Dinneen, and E RussekCohen. 2005 Ruminant Nutrition: Using blood urea nitrogen to predict nitrogen excretion and efficiency of nitrogen utilization in cattle, sheep, goats, horses, pigs, and rats. J. Anim. Sci. 8 3:879 889. Kster, H H., R C Cochran, E C Titgemeyer, E S Vanzant, T G Nagaraja, K K Kreikemeier, and G St Jean. 1997. Effect of increasing proportion of supplemental nitrogen from urea on intake and utilization of low quality, tallgrass prair ie forage by bee f steers. J. Anim. Sci. 75:1393 1399. Krohn, C C., J G Jago, and X Boivin 2001 The effect of early handling on the socialisation of young calves to humans Appl. Anim. Behav. Sci. 74:121 133. Kurz, S G., R M Dyer, Y Hu, M D Wri ght, and M L Day 1990 Regulation of luteinizing hormone secretion in prepubertal heifers fed an energy deficient diet Biol. Reprod. 43( Suppl. 3): 450 456 Lalman, D L., M K Petersen, R P Ansotegui, M W Tess, C K Clark, and J S Wiley 1993 The effects of ruminally undegradable protein, propionic acid, and monensin on puberty and pregnancy in beef heifers J. Anim Sci 71:2843 2852. Lamb, C S. and J Eadie 1979 The effect of barley supplements on the voluntary intake and digestion of low quality roughages by sheep. J. of Agri Sci 92: 235 241. Lapierre, H. and G E Lobley 2001 Nitrogen Recycling in the Ruminant: A Review J. of Dairy Sci. Suppl. 84 : E223 E236. Larson, J E., K N Thielen, B J. Funnell, J S Stevenson, D. J. Kesler and G. C. Lamb. 2009. Influence of a controlled internal drug release after fixed time artificial insemination on pregnancy rates and returns to estrus of nonpregnant cows J. A nim. Sci. 87:914 921.

PAGE 90

90 Laster, D B., G. M. Smith, and K E Gregory 1976. Ch aracterization of biological types of cattle IV Post weaning growth and puberty of heifers J. Anim Sci 43:63 70 Laster, D B., H A Glimp and K E Gregory 1972. Age and weight at puberty and conception in different breeds and breedcrosses of beef heifers J. Anim Sci 34:1031 1036 Laurenz, J C., F M Byers, G T Schelling, and L W Greene. 1991 Effects of season on the maintenance requirements of mature beef cows J. Anim Sci 69:2168 2176. Lesmeister, J L., P J. Burfening, and R L Bla ckwell 1973. Date of first calving in beef cows and subsequent calf production. J. Anim Sci 36:1 6. Little, W., C B Mallinson, D N Gibbons, and G J. Rowlands 1981. Effects of plane of nutrition and season of birth on the age and body weight at puberty of British Friesian heifers Anim Prod 33:273 279 Lobley, G E 1993 Species comparisons of tissue protein metabolism: E ffects of age and hormonal action. J Nutr 123:337 343. Lobley, G E., D Bremner, R Nieto, T Obitsu, A Hotston Moore, and D.S Brown 1998. Transfers of N metabolites across the ovine liver in response to short term infusion of an amino acid mixture into the mesenteric vein. Br J Nutr 80:371 379. Loosli, J K., H H Williams, W E Tho mas, F H Ferris, and L. A Maynard. 1949. Synthesis of amino acids in the rumen. Science. 130: 144 145. Lynch, J M., G. C Lamb, B L Miller, R. T Brandt Jr., R.C Cochran, and J.E Minton. 1997. Influence of timing of gain on growth and reproductive performance of beef replacement heifer s. J. Anim. Sci. 75: 1715 1722. Macrae, A I., D A Whitaker, E Burrough, A Dowell, and J M Kelly 2006. Use of metabolic profiles for the assessment of dietary adequacy in UK dairy herds Vet Rec. 159:655 661. Maeng, W J., C J. Van Nevel, R L Ba ldwin and J G Morris 1976 Rumen microbial growth rates and yields: Effect of amino acids and protein. J. Dairy Sci. 59:64 8 655. Martin, J L., K A Vonnahme, D.C Adams, G P Lardy, and R N Funston. 2007 Effects of dam nutrition on growth and reproductive performance of heifer calves J. Anim. Sci. 85: 841 847 Martin, L C., J S Brinks, R.M Bourdon, and L.V Cundiff 1992 Genetic effects on beef heifer puberty and subsequent reproduction. J. Anim Sci 70: 4006 4017.

PAGE 91

91 Matizha, W., N T Ngongo ni, and J H Topps 1997. Effect of supplementing veld hay with tropical legumes Desmodium uncinatum, Stylosanthes guianensis and Macroptilium atropurpureum on intake, digestibility, outflow rates, nitrogen retention and live weight gain in lambs Anim. F eed Sci. Technol. 69:187 193. Matras, J., S. J. Bartle, and R L Preston. 1991. Nitrogen utilization in growing lambs: Effects of grain (starch) and protein sources with various rates of ruminal degradation. J. Anim Sci 69:339 347 Matton, P. V., V. Ade lakoun, Y Coutur and J.J Dufour 1981. Growth and replacement of the bovine ovarian follicles during the estrous cycle J. Anim. Sci. 52: 813 820. McCann, J. P., and W Hansel 1986. Relationships between insulin and glucose metabolism and pituitary ovari an functions in fasted heifers Biol. Reprod. 34:630 641 McCartor, M. M., R D Randel and L H Carroll. 1979. Effect of dietary alteration of ruminal fermentation on efficiency of growth and onset of puberty in Brangus heifers J. Anim Sci 48:488 494 McShane, T. M., K. K. Schillo, M. J. Estienne, J. A. Boling, N. W. Bradley, and J. B. Hall. 1989. Effects of recombinant DNA derived somatotropin and dietary energy intake on development of beef heifers: Concentrations of hormones and metabolites in blood sera. J. Anim. Sci. 67:2237 2244. Mertens, D R 1977. Dietary fiber components: Relationship to the rate and extent of ruminal digestion. Fed Proc 36:187 192 Minson, D J., and R Milford 1967. The voluntary intake and digestibility of diets containing different proportions of legume and mature pangola grass ( Digitaria decumbens ). Aust. J. Exp. Agric. 7:546 551. Moe, P W 1979. Associated effects of feedstuffs. Pages 177 198 .Pacific Northwest Anita Nutr Conf Morrison, C D., J A Daniel, B J. Holmberg, J Djiane, N. Raver, A Gertler, and D H Keisler 2001. Central infusion of leptin into wellfed and undernourished ewe lambs: Effects on feed intake and serum concentrations of growth hormone and luteinizing hormone. J. Endocrinol 168:31 7 324. Moseley, G. and I R Jones 1979. Some factors associated with the difference in nutritive value of artificially dried red clover and perennial ryegrass for sheep Br J. Nutr 42:139 145. Moseley, W M., M M McCartor, and R D Randel 1977. Effects of monensin on growth and reproductive performance of beef heifers J. Anim Sci 45:961 968

PAGE 92

92 Mosi, A K., and M H Butterworth 1985 The voluntary intake and digestibility of combinations of cereal crop residues and legume hay for sheep. Anim Feed Sci Technol. 12:241 251. Mould, F L., and E R rskov 1983 Manipulation of rumen fluid pH and its influence on cellulosis in sacco, dry matter degradation and the rumen microflora of sheep offered either hay or concentrate Anim Feed Sci Technol 10:1 14. Mould, F., E R rskov, and S O Mann 1983. Associative effects of mixed feeds 2 The effect of dietary additions of bicarbonate salts on the voluntary intake and digestibility of diets containing various proportions of hay and barley Anim Feed Sci. Technol. 10:15 30. Myer, B., L. Warren, J. Eckert, D. Hancock, A. Blount, and C. Olson. 2009. Perennial peanut: Forage nutritional composition and feeding value. University of Florida, Gainesville, FL: IFAS Extension AN 234. Nakazato, M., N. Murakam i, Y. Date, M. Kojima, H. Matsuo, K. Kangawa, and S. Matsukura. 2001. A role for ghrelin in the central regulation of feeding. Nature 409:194 198. Nelsen, T. C., C. R. Long, and T. C. Cartwright. 1982. Postinflection growth in straightbred and crossbred c attle, II, relationships among weight, height, and pubertal characters. J. Anim. Sci. 55:293 304. Newman, Y. C., C. L. Mackowiak, A. R. Blount, and J. Ferrell. 2009. Perennial peanut: A quick reference. University of Florida, Gainesville, FL. IFAS Extension SS AGR 319. Niderkorn V., R. Baumont, A. LeMorvan, and D Macheboeuf 2011. Occurrence of associative effects between grasses and legumes in binary mixtures on in vitro rumen fermentation characteristics J. Anim Sci 89:1138 114 Niderkorn, V., and R Baumont 2009. Associative effects between forages on feed intake and diges tion in ruminants. Animal 3:951 960. Nocek, J. E and J B Russell. 1988. P rotein and energy as an integrated system relationship of ruminal protein and carbohydrate availabilit y to microbial synthesis and milk production. J. of Dairy Sci. 71( Suppl. 8 ) :2070 2107. NRC, 1984 Nutrient Requirements of Beef Cattle. 6th E d Natl Acad Press, Washington, DC. NRC. 2000. Nutrient Requirements of Beef Cattle. 8th E d Natl Acad Press, Wa shington, DC.

PAGE 93

93 Oba, M., and M S Allen 1999. Evaluation of the importance of the digestibility of neutral detergent fiber from forage: Effects on dry matter intake and milk yield of dairy cows. J. Dairy Sci.82:589 596. Osuji, P O 1974 The physiology of eating and the energy expenditure of the ruminant at pasture. J. Range Manage. 27:437 443 Patterson, D J., L R Corah, J R Brethour, M F Spire, J J. Higgins, G H Kiracofe, J S Stevenson, and D D Simms 1991 Evaluation of reproductive traits in Bos taurus and Bos indicus crossbred heifers: effects of postweaning energy manipulation. J. Anim. Sci. 69: 2349 2361. Patterson, D J., R.C. Perry, G.H Kiracofe, R A Bellows, R. B Staigmiller, and L. R Corah. 1992 Management considerations in heifer development and puberty J. Anim Sci. 70: 4018 4035 Perry, R C., L R Corah, R C Cochran, W E Beal, J S Stevenson, J E Minton, D D Simms, and J R Brethour 1991 Influence of dietary energy on follicular development, serum gonadotropi ns, and first postpartum ovulation in suckled beef cows J. Anim Sci 69:3762 3773 Petherick, J. C., R G Holroyd, V J. Doogan, and B K Venus 2002 Productivity, carcass and meat quality of lot fed Bos indicus cross steers grouped according to temperament Aust J. Exp. Agric. 42:389 398. Plasse, D., A C Warnick, and M Koger 1968. Reproductive behavior of Bos Indicus females i n a subtropical environment: Puberty and ovulation frequency in Brahman and Brahman British heifers J. Anim Sci 27:94 100. Poore, M H., J A Moore, T P Eck, R S Swingle, and C B Theurer 1993. Effect of fiber source and ruminal starch degradability on site and extent of digestion in dairy cows J. Dairy Sci. 76:2244 2253 Rakestraw, J., K S Lusby, R P Wettema nn, and J J. Wagner 1986 Postpartum weight and body condition loss and performance of fall calving cows Theriogenology 26:461 473 Ramirez, V D, and S M McCann.1963 Comparison of the regulation of luteinizing hormone secretion in immature an d adult rats. Endocrinology 72: 452 464. Randel, R D., and R C Rhodes, III 1980 The effect of dietary monensin on the luteinizing hormone response of prepubertal heifers given a multiple gonadotropinreleasing hormone challenge. J. Anim Sci 51:925 931 Randel, R D., L M Rutter, and R C Rhodes, III. 1982. Effect of monensin on the estrogeninduced LH surge in prepubertal heifers J. Anim Sci 54:806 810.

PAGE 94

94 Rasmussen, F E., M C Wiltbank, J O Christensen, and R R Grummer. 1996 Effects of fenprostalen e and estradiol 17 benzoate on parturition and retained placenta in dairy cows and heifers J. Dairy Sci. 79:227 234 Reed, B K., Hunt, C W., Sasser, R G., Momont, P A., Rode, L M., Kastelic, J P 1997. Effect of forage: concentrate ratio on digestion and reproduction in primiparous beef heifers J. Anim S ci. 75: 1708 1714. Reynolds, C K., H F Tyrrell, and P J. Reynolds 1991 Effects of diet forage to concentrate ratio and intake on energy metabolism in growing beef heifers: Net nutrient metabolism by visceral tis sues J. Nutr 121:1004 1015. Reynolds, W L., T M De Rouen and J W High 1963. The age and weight at puberty of Angus, Brahman and Zebu cross heifers J Anim Sci 22: 243 (Abstr.). Rhodes III, R. C., M M McCartor, and R D Randel 1978. Effect of feeding protein protected lipids upon growth and reproductive development of yearling heifers J. Anim Sci 46:769 777. Richards, M W., R P Wettemann, and H M Schoenemann. 1989. Nutritional anestrus in beef cows: Body weight change, body condition, l uteinizing hormone in serum and ovarian activity J. Anim Sci 67:1520 1526 Rittenhouse, L. R. and R L Senft 1982. Effects of daily weather fluctuations on the grazing behavior of cattle. Proc Annu Meet West Sect Am Soc Anim Sci 33: 305 307. Robertson, J B., and P J. Van Soest 1975 A note on digestibility in sheep as influenced by lev el of intake. Anim. Prod. 21:89 92. Rutter, L M., and J G Manns 1987. Hypoglycemia alters pulsatile luteinizing hormone secretion in the postpartum beef c ow J. Anim Sci 64:479 488 Rutter, L M., and R D Randel 1984 Postpartum nutrient intake and body condition: Effect on pituitary function and onset of estrus in beef cattle. J. Anim Sci 58:265 274 Savio, J.D., L Keenan, M P Boland, and J F R oche 1988 Pattern of growth of dominant follicles during the oestrous cycle of heifers. J. of Reprod. Fertil. 83: 663 671. Schams, D E Schallenberger, S Gombe, and H Karg 1981 Endocrine patterns associated with puberty in male and female cattle. J Repod. Fertil 30 :103 110. Schillo, K K 1992. Effects of dietary energy on control of luteinizing hormone secretion in cattle and sheep J. Anim Sci 70:1271 1282

PAGE 95

95 Senft, R L., M A Stillwell, and L R Rittenhouse. 1987. Nitrogen and energy budgets o f free roaming cattle J. Range Manage. 40:421 224 Senger, P.L. 2003. Pathways of Pregnancy and Parturition. 2nd ed Cadmus Professional Communications Bellevue, WA Shaffer, K S., P Turk, W R Wagner, and E E D Felton. 2010. Residual feed intake, body composition, and fertility in yearling beef heifers J. Anim. Sci. 89 : 1028 1034. Shintani, M., Y Ogawa, K. Ebihara, M. AizawaAbe, F Miyanaga, T T Hayashi, G Inoue, K Hosoda, M Kojima, K Kangawa, and K Nakao 2001 Ghrelin, an endogenous growth hormone secretagogue, is a novel orexigenic peptide that antagonizes leptin action through the activation of hypothalamic neuropeptide Y/Y1 re ceptor pathway. Diabetes 50:227 232. Short, R E., and R A Bellows 1971 Relationship among weight gains, age at puberty and reproductive performance in heifers J Anim Sci 32:127 131 S irois J., and J E Fortune. 1988. Ovarian follicular dynamics during the estrous cycle in heifers monitored by real time ultrasonography Biol. of Reprod. 39:308 317. Soofi, R., G C. Fahey Jr. and L. L Berger 1982. I n situ and in vivo digestibility and nutrient intakes by sheep of alkali treated soybean stover J. Anim Sci 55:1206 1213. Spicer, L A., C B Theurer, J Sowe, and T H Noon. 1986. Ruminal and post rum inal utilization of nitrogen and starch from sorghum grain, corn and barley based die ts by steers. J. Anim. Sci. 62: 521 530 Staples, C R., R L Fernando, G C Fahey, Jr., L L Berger, and E H Jaster 1984. Effects of intake of a mixed diet by dairy steers on digesti on events. J. Dairy Sci. 67:995 1006. Steiner, R A 1987. Nutritional and metabolic factors in the regulation of reproductive hormone secretion in the primate. Proc Nutr Soc 46:159 175 Stewart, C S., H J. Flint, and M P Bryant 19 97. The rumen bacteria. The Rumen Microbial Ecosystem Pages 113 175. P N Hobson and C S Stewart, ed Chapman and Hall, London, UK. Stewart, T S., C R Long, and T C Cartwright 1980. Characterization of a fivebreed diallel. III Puberty in bulls and heifers J. Anim Sci 50:808 820. Storm, E., and E R rskov 1983. The nutritive value of rumen microorganisms in ruminant 1 Largescale isolation and chemical composition of rumen micr oorganisms. Br. J. Nutr. 50:463 470.

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96 Streeter, M N., D G Wa gner, F N Owens, and C A Hibberd 1989 Combinations of high moisture harvested sorghum grain and dry rolled corn: Effects on site and extent of digestion in beef heifers J Anim Sci 67:1623 1633. Sunderland, S J., M A Crowe, M P Boland, J F Roche, and J J. Ireland. 1994 Selection, dominance and atresia of follicles during the estrous cycle of heifers J Reprod. Fertil 101:547 555. Taniguchi, K., G B Huntington, and B P Glenn 1995. Net nutrient flux by visceral tissues of beef steers g iven abomasal and ruminal infusion of casein and starch. J. Anim Sci 73:236 349 Temple, R S., S H Fowler and J S Evans 1961. Age of puberty in straightbred and crossbred heifers A I Mimeo Cir Pages 61 6 5 Anita Ind Dept., Louisiana State Un iv., Baton Rouge LA Ulyatt, M J., D W Dellow, A John, C S W Reid, and G C Waghorn. 1986 Contribution of chewing during eating and rumination to the clearance of digesta from the ruminoreticulum Control of Digestion and Metabolism in Ruminants Pages 498 515. L.P Milligan, W L Grovum, and A Dobson, ed. PrenticeHall, Englewood Cliffs, NJ. United States Department of Agriculture. 2011 2011 Cattle Inventory Estimates ISSN: 1948 9099 Vadiveloo, J., and W Holmes 1979. The effects of forag e digestibility and concentrate supplementation on the nutritive value of the diet and performance of finishing cattle Anim Prod 29:121 139 Verde, L S., and A Trenkle. 1987. Concentrations of hormones in plasma from cattle with different growth poten tials J. Anim Sci 64: 426 432. Waghorn, G C., I D Shelton, and V J Thomas 1989. Particle breakdown and rumen digestion of fresh ryegrass ( Lolium perenne L.) and lucerne ( Medicago sativa L.) fed to cows during a restricted feeding period. Br J. Nutr 61:409 423. Wagner, J J., K.S Lusby, J W Oltjen, J Rakestraw, R P Wettemann, and L. E Walters 1988. Carcass composition in mature hereford cows: estimation and effect on daily metabolizable energy requirement during winter J. Anim Sci 66: 603 612. Waldman, R C., W J. Tyler, and V H Brungardt 1971 Changes in the carcass composition of Holstein steers associated with ration energy levels and growth. J. Anim Sci 32:611 619. Warnick, A C., W C Burns, M Koger, and M W Hazen. 1956. Puberty in English, Brahman and crossbred breeds of beef heifers Pages 95 101 Proc.of Southern Agric Workers

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97 Wertz Lutz A E., T J. Knight, R H Pritchard, J A Daniel, J A Clapper, A J. Smart, A Trenkle, and D C Beitz 2006. P hysiology, endocrinology, and reproduction: circulating ghrelin concentrations fluctuate relative to nutritional status and influence feeding behavior in cattle. J. Anim Sci 84:3285 3300. Wickersham, T A., E C Titgemeyer, R C Cochran, E E Wickersham, and E S M oore. 2008 Effect of frequency and amount of rumendegradable intake protein supplementation on urea kinetics and microbial use of recycled urea in steers consuming low quality forage J Anim. Sci. 86: 3089 3099 Wiley, J S., M K Petersen, R P Ansotegui, and R A Bellows 1991. Production from first calf beef heifers fed a maintenance or low level of prepartum nutrition and ruminally undegradable or degradable protein postpartum J. Anim Sci 69:4279 4293 Wiltbank, J M., K E Gregory, L A Swige r, J E Ingalls, J A Rothlisberger and R M Koch 1966. Effects of heterosis on age and weight at puberty in beef heifers J. Anim Sci 25:744 751. Wiltbank, J N., C W Kasson and J E Ingalls 1969. Puberty in crossbred and straight bred beef heifers on two levels of feed J. Anim Sci 29:602 605. Woody, H, D., D G Fox and J R Black 1983. Predicting net energy value of corn silage varying in grain content J Anim Sci 57:710 716 Yelich, J V., R. P. Wettemann, H. G. Dolezal, K. S. Lusby D. K. Bishop, D K., and L. J. Spi cer. 1995 Effects of growth rate on carcass composition and lipid partitioning at puberty and growth hormone, insulinlike growth factor I, insulin, and metabolites before puberty in beef heifers J. Anim Sci 73: 2390 2405. Young, B A 1983. Ruminant cold stress: Effect on product ion. Can. J. Anim. Sci. 57:1601 1607.

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98 BIOGRAPHICAL SKETCH Kalyn M Bischoff was born in Spearfish, S outh D akota, to Gary and Paula Bischoff She grew up on her familys cow calf operation in southeastern Montana where she was actively involved in 4H and FFA Kalyn graduated from Hulett High School, H ulett, Wyoming in 2004 and began her educational career at Northwest Junior College where she received her associates in agricultural communicat ions After graduat ions she moved to Stillwater, Oklahoma where she completed her Bachelor of Science degree in the field of Animal Science at Oklahoma State University Upon graduation, she moved to Florida to work in Dr Cliff Lambs research program, w here she has focused her studies on replacement heifer development and applied reproductive strategies in beef cattle. She was also a teaching assistant for various animal science reproduction courses She will begin her PhD in Augus t of 2011 in Dr Lamb s program at the University of Florida.