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Co-Product and Degradable Intake Protein Supplementation of Beef Cattle Fed Bahiagrass Forage

Permanent Link: http://ufdc.ufl.edu/UFE0021782/00001

Material Information

Title: Co-Product and Degradable Intake Protein Supplementation of Beef Cattle Fed Bahiagrass Forage
Physical Description: 1 online resource (83 p.)
Language: english
Creator: Wahrmund, Jacqueline L
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2007

Subjects

Subjects / Keywords: acid, adg, ammonia, bahiagrass, bcs, beef, bw, cattle, cow, dip, distillers, dried, energy, fatty, forage, glucose, grains, hay, hulls, intake, low, nitrogen, ph, plasma, protein, pun, quality, rdp, soybean, steer, synchronized, synchrony, urea, urine, vfa, volatile
Animal Sciences -- Dissertations, Academic -- UF
Genre: Animal Sciences thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Beef cattle consuming subtropical grass based diets are often deficient in CP. Two experiments were conducted with the objective of evaluating the effects of feeding Optigen? II with co-product supplements on animal performance and blood metabolites in beef cows and growing calves. A third trial was conducted with the objective of evaluating two co-product supplements, either alone or in combination, on performance and blood metabolites of growing calves. All experiments were conducted as completely random designs and analyzed with the Mixed procedure of SAS; individual animal was the experimental unit. In the first experiment, 22 non-pregnant cows were individually fed bahiagrass hay and supplemented with 0.82 kg of dried citrus pulp for 56 d. Treatments included 1) Control (no supplemental N); 2) Urea, 0.11 kg Urea , 3) Optigen 0.11 kg Optigen? II. On d 0, 28, and 56 cow BW and BCS were recorded and blood samples were collected for analysis of plasma urea nitrogen (PUN) and glucose concentrations. There were no treatment differences on d 56 for cow BW, BCS, or blood glucose concentrations (P=0.78, 0.94, 0.88). Cows receiving supplemental N had greater (P < 0.001) PUN concentrations than Control on d 28 and 56. Plasma urea-N concentrations of Optigen-fed cows on d 28 tended (P=0.10) to be less than that of cows offered urea. In the other two experiments, 56 Angus steers were allowed ad libitum access to bahiagrass hay and were supplemented via a Calan gate system. Bodyweights were recorded, and blood samples were obtained for analysis of PUN and glucose concentrations on d 0, 14, 28, and 56. Steers were blocked by BW and randomly assigned to one of four treatments. In Trial One, treatments included 1) DDG, 1.19 kg dried distillers grains (DDG); 2) DDG+Opt, 1.19 kg DDG, 45.5 g Optigen; 3) SBH, 2.63 kg soybean hulls (SBH); 4) SBH+Opt, 2.63 kg SBH, 45.5 g Optigen. Amounts of DDG and SBH were formulated to supply equal amounts of CP. On d 42, there were no treatment differences for steer BW, ADG, or blood glucose concentrations (P=0.97, 0.17, 0.54, respectively). Across all days, steers offered only DDG had greater (P < 0.05) PUN concentrations than steers offered SBH. On d 14, 28, and 42, Optigen-supplemented steers had greater (P < 0.05) PUN concentrations compared to those that were not. In Trial Two, isoenergetic treatments included 1) DDG, 2.8 kg; 2) DDG/SBH, 1.93 kg DDG, 0.98 kg SBH; 3) SBH/DDG, 0.96 kg DDG, 2.05 kg SBH; 4) SBH, 3.12 kg. Supplement treatment had no effect (P=0.79) on final BW. Overall 42-d ADG of steers supplemented with SBH was less than that of DDG/SBH (P=0.06, 0.80 kg/d) or SBH/DDG (P=0.03, 0.83 kg/d), but was not different (P=0.45) than DDG-supplemented steers. Plasma glucose concentrations were not affected (P=0.85) by treatment. On d 0, PUN concentrations did not differ (P=0.65). On d 14, 28, and 42 PUN concentrations increased (P < 0.05) with the amount of DDG included in the supplement. Supplementing steers consuming low-quality forage with a combination of co-products resulted in improved BW gain and N metabolism. The SBH/DDG treatment optimized calf performance. Beef cattle consuming bahiagrass hay require additional dietary CP to maintain performance and promote ADG. Energy supplementation may compliment natural protein supplementation; however additional DIP may not be necessary. If DIP supplements are utilized, the rate of N release does not affect cattle performance.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Jacqueline L Wahrmund.
Thesis: Thesis (M.S.)--University of Florida, 2007.
Local: Adviser: Hersom, Matthew J.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2008-12-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2007
System ID: UFE0021782:00001

Permanent Link: http://ufdc.ufl.edu/UFE0021782/00001

Material Information

Title: Co-Product and Degradable Intake Protein Supplementation of Beef Cattle Fed Bahiagrass Forage
Physical Description: 1 online resource (83 p.)
Language: english
Creator: Wahrmund, Jacqueline L
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2007

Subjects

Subjects / Keywords: acid, adg, ammonia, bahiagrass, bcs, beef, bw, cattle, cow, dip, distillers, dried, energy, fatty, forage, glucose, grains, hay, hulls, intake, low, nitrogen, ph, plasma, protein, pun, quality, rdp, soybean, steer, synchronized, synchrony, urea, urine, vfa, volatile
Animal Sciences -- Dissertations, Academic -- UF
Genre: Animal Sciences thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Beef cattle consuming subtropical grass based diets are often deficient in CP. Two experiments were conducted with the objective of evaluating the effects of feeding Optigen? II with co-product supplements on animal performance and blood metabolites in beef cows and growing calves. A third trial was conducted with the objective of evaluating two co-product supplements, either alone or in combination, on performance and blood metabolites of growing calves. All experiments were conducted as completely random designs and analyzed with the Mixed procedure of SAS; individual animal was the experimental unit. In the first experiment, 22 non-pregnant cows were individually fed bahiagrass hay and supplemented with 0.82 kg of dried citrus pulp for 56 d. Treatments included 1) Control (no supplemental N); 2) Urea, 0.11 kg Urea , 3) Optigen 0.11 kg Optigen? II. On d 0, 28, and 56 cow BW and BCS were recorded and blood samples were collected for analysis of plasma urea nitrogen (PUN) and glucose concentrations. There were no treatment differences on d 56 for cow BW, BCS, or blood glucose concentrations (P=0.78, 0.94, 0.88). Cows receiving supplemental N had greater (P < 0.001) PUN concentrations than Control on d 28 and 56. Plasma urea-N concentrations of Optigen-fed cows on d 28 tended (P=0.10) to be less than that of cows offered urea. In the other two experiments, 56 Angus steers were allowed ad libitum access to bahiagrass hay and were supplemented via a Calan gate system. Bodyweights were recorded, and blood samples were obtained for analysis of PUN and glucose concentrations on d 0, 14, 28, and 56. Steers were blocked by BW and randomly assigned to one of four treatments. In Trial One, treatments included 1) DDG, 1.19 kg dried distillers grains (DDG); 2) DDG+Opt, 1.19 kg DDG, 45.5 g Optigen; 3) SBH, 2.63 kg soybean hulls (SBH); 4) SBH+Opt, 2.63 kg SBH, 45.5 g Optigen. Amounts of DDG and SBH were formulated to supply equal amounts of CP. On d 42, there were no treatment differences for steer BW, ADG, or blood glucose concentrations (P=0.97, 0.17, 0.54, respectively). Across all days, steers offered only DDG had greater (P < 0.05) PUN concentrations than steers offered SBH. On d 14, 28, and 42, Optigen-supplemented steers had greater (P < 0.05) PUN concentrations compared to those that were not. In Trial Two, isoenergetic treatments included 1) DDG, 2.8 kg; 2) DDG/SBH, 1.93 kg DDG, 0.98 kg SBH; 3) SBH/DDG, 0.96 kg DDG, 2.05 kg SBH; 4) SBH, 3.12 kg. Supplement treatment had no effect (P=0.79) on final BW. Overall 42-d ADG of steers supplemented with SBH was less than that of DDG/SBH (P=0.06, 0.80 kg/d) or SBH/DDG (P=0.03, 0.83 kg/d), but was not different (P=0.45) than DDG-supplemented steers. Plasma glucose concentrations were not affected (P=0.85) by treatment. On d 0, PUN concentrations did not differ (P=0.65). On d 14, 28, and 42 PUN concentrations increased (P < 0.05) with the amount of DDG included in the supplement. Supplementing steers consuming low-quality forage with a combination of co-products resulted in improved BW gain and N metabolism. The SBH/DDG treatment optimized calf performance. Beef cattle consuming bahiagrass hay require additional dietary CP to maintain performance and promote ADG. Energy supplementation may compliment natural protein supplementation; however additional DIP may not be necessary. If DIP supplements are utilized, the rate of N release does not affect cattle performance.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Jacqueline L Wahrmund.
Thesis: Thesis (M.S.)--University of Florida, 2007.
Local: Adviser: Hersom, Matthew J.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2008-12-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2007
System ID: UFE0021782:00001


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1 CO PRODUCT AND DEGRADABLE INTAKE PROTEIN SUPPLEMENTATION OF BEEF CATTLE FED BAHIAGRASS FORAGE By JACQUELINE LOUISE WAHRMUND A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF T HE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2007

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2 2007 Jacqueline Louise Wahrmund

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3 This thesis is dedicated to the memory of my parents, Donald C. and Janis F. Wahrmund, for giving me motivation in all my endeavors, and for being the stars that light the way.

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4 ACKNOWLEDGMENTS I would like to thank the chair of my supervisory committee, Dr. Matt Hersom, for his endless dedication, support, and patience throughout my degree program. I am also very thankful to Dr. Bill Brown and Dr. John Arthington for their kind ness and input as members of my committee. I am very thankful to the other members of my laboratory, Ashley Hughes, Dusty Holley, and Reyna Speckmann, for their assistance during my research. I also thank Davi Brito de Arajo, Reinaldo Cooke, Toni Wood, a nd the staff at the Range Cattle Research and Education Center for their assistance during my 2006 cow trial. I am also very appreciative of the assistance I received from Danny Driver and the crew at the Beef Research Unit for their dedication to my 2006 steer trials. Completion of my work in the laboratory would not have been possible without the help of the supportive lab technicians in the Animal Sciences department: Nancy Wilkinson, Jan Kivipelto, Frank Robbins, Sergei Sennikov, and Max Huisdin. I wo uld like to thank my friends, Jamie Foster, Jessica Belsito, Cristina Caldari Torres, Kelly Vineyard, Sergio Madrid, Sarah Dilling and Ashley Hughes, for making my time in Florida so memorable. This experience would not have been worth it without having e ach of you here with me, and I will miss you. Finally, I must thank my family for their endless support. I am especially thankful to my grandparents, Fred and Peggy Fischer, who are always ready to lend an ear when I need them, and have always helped me t throughout my life.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ ............... 4 LIST OF TABLES ................................ ................................ ................................ ........................... 7 ABSTRACT ................................ ................................ ................................ ................................ ..... 8 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .................. 10 2 REVIEW OF LITERATURE ................................ ................................ ................................ 12 Nutritional Requirements of Beef Cattle ................................ ................................ ................ 12 Protein Content of Tropical and Subtropical Forages ................................ ............................ 13 Protein Supplementation ................................ ................................ ................................ ......... 14 Natural Protein ................................ ................................ ................................ ................. 16 Animal performance ................................ ................................ ................................ 17 Forage intake ................................ ................................ ................................ ............ 18 Digestibility ................................ ................................ ................................ .............. 18 Physiological responses ................................ ................................ ............................ 19 Non Protein Nitrogen ................................ ................................ ................................ ...... 21 Animal performance ................................ ................................ ................................ 21 Forage intake ................................ ................................ ................................ ............ 22 Digestibility ................................ ................................ ................................ .............. 23 Physiological responses ................................ ................................ ............................ 24 Energy Supplementation ................................ ................................ ................................ ......... 25 Theory of Nutrient Synchrony ................................ ................................ ................................ 26 3 UREA AND OPTIGEN II AS SOURCES OF DEGRADABLE INTAKE PROTEIN FOR MATURE BEEF COWS ................................ ................................ ............................... 32 Introduction ................................ ................................ ................................ ............................. 32 Mat erials and Methods ................................ ................................ ................................ ........... 33 Animals and Diets ................................ ................................ ................................ ........... 33 Sampling and Analysis ................................ ................................ ................................ .... 34 Statistical Analysis ................................ ................................ ................................ .......... 35 Results and Discussion ................................ ................................ ................................ ........... 36 Cow Performance ................................ ................................ ................................ ............ 36 Physiological Response ................................ ................................ ................................ ... 39 Implications ................................ ................................ ................................ ............................ 45 4 EVALUATION OF DRIED DISTILLERS GRAINS AND SOYBEAN HULLS AS SUPPLEMENTS FOR GR OWING BEEF STEERS CONSUMING BAHIAGRASS HAY ................................ ................................ ................................ ................................ ........ 49

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6 Introduction ................................ ................................ ................................ ............................. 49 Materials and Methods ................................ ................................ ................................ ........... 50 Animals and Diets ................................ ................................ ................................ ........... 50 Trial one ................................ ................................ ................................ ................... 50 Trial two ................................ ................................ ................................ ................... 51 Sampling and Analysis ................................ ................................ ................................ .... 51 Statistical Analysis ................................ ................................ ................................ .......... 53 Results and Discussion ................................ ................................ ................................ ........... 54 Trial One ................................ ................................ ................................ .......................... 54 Steer performance ................................ ................................ ................................ .... 54 Physiological response ................................ ................................ ............................. 57 Trial Two ................................ ................................ ................................ ......................... 62 Steer performance ................................ ................................ ................................ .... 62 Physiological response ................................ ................................ ............................. 63 Economic analysis ................................ ................................ ................................ .... 66 Implications ................................ ................................ ................................ ............................ 66 LIST OF REFERENCES ................................ ................................ ................................ ............... 73 BIOGRAPHICAL SKETCH ................................ ................................ ................................ ......... 83

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7 LIST OF TABLES Table page 3 1. Composition of feedstuffs fed to mature cows. ................................ ................................ ..... 46 3 2. Effect of supplemental NPN sourc e on cow bodyweight (BW) and body condition score (BCS). ................................ ................................ ................................ ....................... 46 3 3. Effect of supplemental NPN source on hay dry matter intake (DMI) of mature cows. ........ 47 3 4. Effect of supplemental NPN source on plasma concentrations of glucose and urea nitrogen of mature cows. ................................ ................................ ................................ .... 47 3 5. Effect of supplemental NPN source on ruminal fluid pH, ammonia N, and total VFA concentration. ................................ ................................ ................................ ..................... 48 4 1. Composition of feedstuffs fed to growing beef steers. ................................ .......................... 68 4 2. Effect of co product source and Optigen II supplementation on steer bodyweight (BW), BW gain and intake (Trial One). ................................ ................................ ............ 69 4 3. Effect of co product source and Optigen II supplementation on steer plasma g lucose and urea nitrogen concentration (Trial One). ................................ ................................ ..... 70 4 4. Effect of co product source and Optigen II supplementation on daily urinary nitrogen excretion (Trial One). ................................ ................................ ................................ ......... 70 4 5. Effect of dried distillers grains (DDG) and/or soybean hulls (SBH) supplementation on steer bodyweight (BW), BW gain and intake (Trial Two). ................................ ............... 71 4 6. Effect of dried distillers grains (DDG) and/or soybean hulls (SBH) supplementation on steer plasma glucose and urea nitrogen concentration. ................................ ...................... 72 4 7. Economics of supplementing dried d istillers grains (DDG) or soybean hulls (SBH). .......... 72

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8 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 CO PRODUCT AND DEGRADABLE INTAKE PROTEIN SUPPLEMENTATION OF BEEF CATTLE FED BAH IAGRASS FORAGE By Jacqueline Louise Wahrmund December 2007 Chair: Matt Hersom Major: Animal Sciences Beef cattle consuming subtropical grass based diets are often deficient in CP. Two experiments were conducted with the objective of evaluating the effec ts of feeding Optigen II with co product supplements on animal performance and blood metabolites in beef cows and growing calves. A third trial was conducted with the objective of evaluating two co product supplements, either alone or in combination, on p erformance and blood metabolites of growing calves. All experiments were conducted as completely random designs and analyzed with the Mixed procedure of SAS; individual animal was the experimental unit. In the first experiment, 22 non pregnant cows were individually fed bahiagrass hay and supplemented with 0.82 kg of dried citrus pulp for 56 d. Treatments included 1) Control (no supplemental N) ; 2) Urea 0.11 kg Urea 3) Optigen 0.11 kg Optigen II On d 0, 28, and 56 cow BW and BCS were recorded and bl ood samples were collected for analysis of plasma urea nitrogen ( PUN ) and glucose concentrations. There were no treatment differences on d 56 for cow BW, BCS, or blood glucose concentrations ( P =0.78, 0.94, 0.88). Cows receiving supplemental N had greater ( P <0. 001) PUN concentrations than Control on d 28 and 56. Plasma urea N concentrations of Optigen fed cows on d 28 tended ( P =0.10 ) to be less than that of cows offered u rea. In the other two experiments, 56 Angus steers were allowed ad libitum access to bahiagrass hay and were

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9 supplemented via a Calan gate system. Bodyweights were recorded, and blood samples were obtained for analysis of PUN and glucose concentrations on d 0, 14, 28, and 56. Steers were blocked by BW and randomly assigned to one of fou r treatments. In Trial One, treatments included 1) DDG 1.19 kg dried distillers grains (DDG); 2) DDG+Opt 1.19 kg DDG, 45.5 g Optigen; 3) SBH 2.63 kg soybean hulls (SBH); 4) SBH+Opt 2.63 kg SBH, 45.5 g Optigen. Amounts of DDG and SBH were formulated t o supply equal amounts of CP. On d 42, there were no treatment differences for steer BW, ADG, or blood glucose concentrations ( P =0.97, 0.17, 0.54 respectively ). Across all days, steers offered only DDG had greater ( P <0.05) PUN concentrations than steer s offered SBH. On d 14, 28, and 42, Optigen supplemented steers had greater ( P <0.05) PUN concentrations compared to those that were not In Trial Two, isoenergetic t reatments included 1) DDG 2.8 kg; 2) DDG/SBH 1.93 kg DDG, 0.98 kg SBH; 3) SBH/DDG 0.96 kg DDG, 2.05 kg SBH ; 4) SBH 3.12 kg. Supplement treatment had no effect ( P =0.79 ) on final BW. Overall 42 d ADG of steers supplemented with SBH was less than that of DDG/SBH ( P =0.06, 0.80 kg/d) or SBH/DDG ( P =0.03, 0.83 kg/d), but was not different ( P =0. 45) than DDG supplemented steers. Plasma glucose concentrations were not affected ( P =0.85 ) by treatment. On d 0, PUN concentrations did not differ ( P =0.65 ). O n d 14, 28, and 42 PUN concentrations increased ( P <0.05) with the amount of DDG included in the supplement Supplementing steers consuming low quality forage with a combination of co products resulted in improved BW gain and N metabolism. The SBH/DDG treatment optimized calf performance. Beef cattle consuming bahiagrass hay require additional die tary CP to maintain performance and promote ADG. Energy supplementation may compliment natural protein supplementation; however additional DIP may not be necessary. If DIP supplements are utilized, the rate of N release does not affect cattle performance

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10 CHAPTER 1 INTRODUCTION Cow/calf operations are the most common type of beef cattle production system in Florida. Forage constitutes a majority of the diet for these cattle, and nutritional programs are centered around the nutrient availability of the fora ge. Bahiagrass is the most common type of forage utilized in Florida (Chambliss and Sollenberger, 1991); however, at certain points of the production cycle, cattle are not able to consume enough bahiagrass to meet their nutrient requirements. Therefore, supplementation programs must be developed to optimize beef cattle performance. Bahiagrass in Florida generally does not contain enough protein to meet cattle requirements. Growing calves, that require high levels of protein to support tissue growth, are particularly susceptible to protein deficiencies on low quality forage based diets. There are a variety of protein supplements available to cattle producers, including plant and animal protein by products, as well as NPN supplements, such as urea. The pr ice of the feedstuffs, as well as the nutrient needs of the animal, will generally dictate the most economically desirable supplementation program to optimize herd performance. Intake of low quality forages can be limited by gut fill (Allen, 1996); there fore, cattle may also benefit from additional supplementation to meet their energy requirements. Supplement feeds that are high in fermentable fiber and low in starch provide the most effective sources of energy for cattle on high forage diets, as starch may interfere with fiber digestion within the rumen (Richards et al., 2006). When selecting protein or energy feeds, factors of consideration include the effects on animal performance, forage intake, and physiological effects, such as blood metabolites an d rumen metabolism.

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11 The rumen microbes require energy and N to synthesize microbial protein, which is an the rumen has been hypothesized to have an impact on the efficiency of microbial protein synthesis. Diets which provide both energy and N at a similar rate should theoretically enhance microbial protein synthesis, and in turn, promote improved animal performance. The following discussion will outline the princi ples of protein and energy supplementation for beef cattle consuming low quality forages. Sources of natural protein and NPN have been used successfully to enhance beef cattle performance and intake, as well as diet digestibility. Three trials were condu cted to observe the effects of various protein sources with a range of rates and extents of rumen degradabilities. The relationships between these protein sources and energy consumption will also be discussed.

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12 CHAPTER 2 REVIEW OF LITERATURE Nutritional Requirements of Beef Cattle There are six classes of nutrients required by beef cattle: carbohydrates, protein, lipids, vitamins, minerals, and water. This review will focus on the protein requirements of beef ca ttle, and the relationship of protein and energy in the diets of forage fed cattle. Most energy is obtained through consumption of carbohydrates, with protein and lipid sources also supplying energy (Russell et al., 1992). The net energy required for mai ntenance (NE m ) is equal to the amount of energy intake that does not cause a gain or loss of BW by the animal (NRC, 2000). In growing cattle, the amount of energy that is consumed above NE m and is converted into new tissue growth, is considered net energ y for growth. The nutritional and energy requirements of beef cattle are dependent on many factors, including, but not limited to, age, physiological state, breed, temperature, and season. The amount of energy required for maintenance decreases with age ( Corbett et al., 1985; Carstens et al, 1989 ). Bos indicus cattle have lower maintenance energy requirements than Bos taurus cattle, which in turn, have lower maintenance requirements than dairy type cattle. Breed effects also interact with season and tem perature effects. Maintenance energy requirements have been shown to be less for Angus cattle in the winter, while Simmental cattle have lowest maintenance requirements during the summer ( Laurenz et al., 1991 ). There is a mutual relationship between the r uminant animal and the microbes that live within the rumen. The ruminant animal provides the microbes with sources of energy and N, and the microbes in turn provide the animal with volatile fatty acids (VFA) for energy metabolism and microbial protein. R uminants not only require dietary protein to support the physiological and metabolic functions of the animal, but sources of ruminally available N are also needed to

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13 support microbial production. The maintenance protein requirements of cattle are generall y low, as protein is only required to sustain the rumen microbial population and to replace tissue turnover (rskov, 1982). Cattle are able to survive on very low levels of dietary protein. It has been suggested that the rumen microbes are able to surviv e with ammonia N concentrations as low as 0.3 mg/dL (Owens and Zinn, 1993). However, while cattle may survive at these low levels of dietary CP, much greater levels are needed to support requirements for gestation, lactation, and growth. Protein Content o f Tropical and Subtropical Forages Cow calf operations are the principal beef production systems found throug hout the state of Florida. Cow calf production systems are heavily dependent on grazed and conserved forages. However, both the quantity and qual ity of the forage may limit cattle production during certain times of the year. Producers may potentially improve cattle production through either forage quality improvements or through supplementation. Bahiagrass ( Paspalum notatum ) is the most common su btropical forage utilized by beef producers in Florida The growing season of bahiagrass is from early March through mid December in South Florida, and from April through November in North Florida (Chambliss and Sollenberger, 1991). Bah iagrass generally contains approximately 8% CP on a dry matter basis (NRC, 2000). Performan ce of beef cattle consuming sub tropical forages has been improved through both protein supplementation (Brown and Adjei, 2001) and ammoniation of hay (Brown, 1988 ) These results wo uld imply that subtropical forages are often low quality and that protein concentration limits animal performance. The seasonal trends of forage nutrient composition must be considered when developing supplementation programs for cattle consuming sub t ropic al forage based diets. Gener ally peak forage mass occurs mid summer; however, peak forage mass is also associated with depressed forage quality (Sollenberger et al., 1989). In a study by Arthington and Brown (2005) CP

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14 concentrations of subtropical fora ges decreased by 38% when allowed 10 wk compared to 4 wk of regrowth Protein Supplementation Protein is an essential nutrient in the d iets of ruminant animals. Ruminants obtain protein substrates through dietary sources and through microbes which live an d reproduce within the rumen of the animal. Sources of dietary CP from feedstuff s may contain either natural p rotein or NPN. Natural proteins are characterized as sources of N that contain naturally occurring amino acid polymers, and may include a variet y of feeds of both plant and animal origin, such as soybean meal ( SBM ) cottonseed meal, feather meal, and fish meal. Sources of NPN are classified as N containing compounds which are not composed of amino acid chains, such as urea and biuret. Dietary CP is further classified as either degradable intake protein ( DIP ) or undegradable intake protein ( UIP ). The protein portion that undergoes degradation by the rumen microbes is considered DIP, while the remaining UIP portion bypasses the rumen and enters the small intestine undegraded. During rumen degradation, the protein is broken down into peptides and amino acids, which are either utilized by the rumen microbes, or broken down further, removing the N group (deamination) for use as ammonia by the rumen mi crobes. Sources of NPN, such as urea and biuret, are 100% DIP, as a percentage of CP. Undegradable intake protein does not undergo rumen degradation. Therefore, it is also obes, and instead passes to the small intestine. Here, the protein is digested by intestinal peptidases into amino acids, which are absorbed across the small intestine as either free amino acids or peptides (Webb and Matthews, 1994).

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15 Ruminants require DIP in order to maintain a healthy, functioning rumen environment. Rumen microbes depend on N containing compounds, such as amino acids and ammonia, to support their growth and reproduction. These requirements for DIP are often met with dietary sources. Ho wever, when protein intake is low cattle depend on N recycling to provide essential N supplies to the rumen (Russell et al., 1992). One method of N recycling involves transporting N through the saliva. High forage diets require more rumination, which inc reases saliva production by the animal. Therefore, saliva may supply more N to the rumen in grazing animals than cattle consuming high concentrate diets (Owens and Zinn, 1993). Nitrogen may also be delivered to the rumen through the blood. Nitrogen is c onverted to urea in the liver, and is then circulated through the blood as plasma urea nitrogen ( PUN ) or ammonia. Rumen microbes convert urea to ammonia N for use in the synthesis of microbial protein (Krehbiel et al., 1998). Nitrogen recycling via the b lood is greatest when rumen ammonia concentrations are low. The amount of N that appears at the duodenum may be greater than N intake as a result of N recycling when dietary protein intake is low (Owens and Zinn, 1993). Kster et al. (1996 ) determined tha t mature cows require 11% DIP as a percentage of digestible OM. While microbial efficiency and true organic matter digestibility increased linearly with increasing levels of DIP supplementation, a quadratic effect was observed with respect to forage DMI, as forage DMI decreased at the greatest level of DIP supplementation. While DIP is a necessary dietary constituent, UIP may improve cattle performance by supplying amino acids directly to the animal. Kalmbacher et al. (1995) concluded that compared to ur ea, SBM improved OM digestibility of low quality bluestem hay fed to Brahman crossbred steers. Additionally, the inclusion of cottonseed meal or feather meal to molasses and urea supplements improved ADG and feed efficiency of steers allowed ad libitum ac cess to ammoniated stargrass

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16 hay (Kalmbacher et al., 1995). However, increasing levels of UIP supplementation do not necessarily result in linear responses in animal performance. A trial conducted by Sletmoen Olson et al. (2000 ) observed the effects of i ncreasing levels of UIP in supplements containing equal amounts of energy and DIP when fed to gestating and lactating cows consuming ad libitum low quality cool season prairie grass hay. Supplementation of UIP improved cow BW, BCS, and OM intake compared to a negative control; however, low levels of UIP supplementation were as effective as high levels of UIP at improving animal performance when DIP were met with lo w levels of UIP, and additional protein was not necessary. Natural Protein Natural proteins are distinct from NPN sources in that they contain essential amino acids, and usually a portion of the protein bypasses rumen degradation, making the amino acids po tentially available to the animal in the small intestine. The degree to which the protein is degraded depends on the source from which it came, as well as any processing the feed may have undergone. Animal proteins typically have much greater concentrati ons of UIP compared to most plant proteins. Also, feeds that have undergone heat treatment typically contain a greater portion of UIP compared to most other protein sources as heat treated protein is not as available to rumen microbes for degradation A dditionally, heat treatment may damage the UIP portion of the feed protein so that it is also unavailable for digestion by the animal in the small intestine. Many animal by product meals, such as feather, fish, blood, and bone meals, undergo extensive hea t treatment to destroy harmful bacteria, and as a result contain more UIP than DIP (NRC, 2000). Feather meal contains approximately 30% DIP whereas more than half the protein in cottonseed meal is ruminally degradable (NRC, 2000). While most plant prote ins, such as SBM, cottonseed meal, and corn gluten feed contain mostly DIP, dried distillers grains ( DDG ) are a

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17 source of plant protein which is predominantly UIP. Distillers grains, a co product of ethanol production, typically contain about 11% fat and high amounts of fermentable fiber, and therefore, may also be utilized as a source of supplemental energy (Loy et al., 2007). The supply of DDG as a feed resource is increasing each year as the amount of ethanol production continues to rise. The role of DDG in the diets of beef cattle consuming low quality forages must be further explored to determine the most effective method of supplementation. Animal performance Supplementation of low quality forage with natural protein typically results in improved co w performance (Pate et al., 1990; Hussein and Jordan, 1991; Bohnert et al., 2002b) and greater ADG in growing calves ( Poppi and McLennan, 1995 ; Poore et al., 2006; MacDonald et al., 2007) Pate et al. (1990) observed greater pregnancy rates in cows and fi rst calf heifers grazing bahiagrass pasture and offered supplements of molasses with urea and cottonseed meal compared to molasses alone. DelCurto et al. (1990a) reported the effects of increasing levels of CP supplementation (13%, 25%, 39% CP) when SBM w as used as the source of natural protein on the performance of pregnant cows grazing dormant tallgrass prairie. Bodyweight and BCS loss decreased linearly as supplement CP increased post calving (120 d). Likewise, greater supplement CP concentrations res ulted in greater BW and BCS gain prior to the breeding season (55 d). Average daily gain of heifers grazing bromegrass pasture has been shown to increase with the amount of supplemental DDG (MacDonald et al., 2007). Brown and Pate (1997) reported that AD G and gain efficiency of steers consuming ammoniated stargrass hay increased with the amount of cottonseed meal or feather meal included in molasses supplements with urea. When dietary protein from forage is not adequate, supplementation with natural prot ein sources is effective at improving animal performance.

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18 Forage intake The supplementation of low quality forage diets with natural protein has been shown to result in decreased voluntary forage DMI (Moore et al., 1999); however, varying results have been reported. F orage DMI of steers grazing dormant tallgrass prairie was maximized in steers receiving moderate levels of protein (79% of CP requirement) compared to steers receiving either low or high SBM based protein supplements ( 40 or 120% of CP requirem ents; DelCurto et al., 1990a ). A similar quadratic response was observed by Huntington et al. (2001) when SBM supplements were included in a corn silage diet for beef steers. No differences in hay intake were observed when beef steers consuming bermudagr ass hay received ruminal infusions of sodium caseinate (Mathis et al., 2000). Other studies have also shown no differences in intake once protein requirements have been met or exceeded (Church and Santos, 1981; Hennessy et al., 1983). Supplementation of protein will generally decrease hay DMI when the ratio of TDN:CP is less than 7, while ratios above 12 may indicate a potential for supplementation to increase forage intake (Moore et al., 1999). Ratios below 7 indicate that forage protein is adequate rel ative to available energy. Protein supplements may substitute for voluntary forage intake. Therefore, protein supplements should be offered at levels which stimulate intake; however, levels that exceed animal requirements will not be economical or benefi cial to animal performance and intake. Digestibility The digestibility of low quality forage diets may be improved by providing supplements containing sources of natural protein (Kster et al., 1996) DelCurto et al. ( 1990b ) observed the effects of increa sing levels of protein supplementation on digestibility of dormant tallgrass prairie forage in steers. Compared to steers receiving no supplemental protein, total dry matter digestibility was greater when steers were offered SBM based supplements containi ng 12, 28, or

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19 41% CP. Kalmbacher et al. (1995) also reported greater OM digestibility when SBM was used as a supplement to bluestem hay for mature beef cows. Hannah et al. (1991) offered two levels of SBM based protein supplements or a supplement of alfa lfa pellets to steers consuming bluestem range forage. True diet OM digestibility increased when supplements contained alfalfa pellets (18% CP), or 27% CP from SBM; however, diet OM digestibility did not increase when supplements contained 13% CP from SBM When forages are very low in CP, the ability of rumen microbes to digest fiber will likely be limited by the amount of N substrates needed to support microbial growth (Kster et al., 1996). Supplementing protein to low quality forages enhances the nutr ient supply to the microbes, which will typically increase fiber digestion by rumen microbes, and overall diet digestibility. Physiological responses There are a variety of ways that protein supplements affect physiological measures of ruminants, including plasma and urine metabolites and rumen fermentation characteristics. Hammond et al. (1993) outlined how PUN concentrations are used as an indicator of protein and energy status of beef cattle consuming low quality forages. Concentrations between 9 and 1 2 mg/dL indicate adequate protein and energy status. Concentrations below 9 mg/dL indicate that protein is deficient, and PUN concentrations above 12 mg/dL may signify that protein is in excess in relation to energy, and therefore, supplemental energy may enhance cattle performance. Poore et al. (2006) conducted a two year experiment observing the effects of supplementing whole cottonseed to beef heifers consuming fescue pasture. The protein content of the forage was greater during year one, and PUN conce ntrations in heifers fed the control diet were above 9 mg/dL. During year two, the protein content of the forage decreased, resulting in PUN concentrations of 7.8 mg/dL for control heifers. The PUN concentrations associated with

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20 the all forage control di et may help explain why heifers responded more to whole cottonseed supplementation during year two with respect to ADG. Plasma urea nitrogen concentrations during year one implied that dietary protein was adequate, while the low PUN concentrations during the second year indicated that forage protein may have been deficient during year two Rumen pH concentrations have generally been unaffected by protein supplementation in ruminants consuming low quality forage. DelCurto et al. (1990b) did not observe chan ges in pH as a result of feeding SBM to steers consuming dormant tallgrass prairie forage. Also, Salisbury et al. (2003) reported no differences in rumen pH of wethers offered SBM or feather meal as a supplement to low quality hay. However, decreased rum en fluid pH has been reported when steers consuming low quality forage received ruminal infusions of sodium caseinate (Kster, 1996), which was likely the result of increased rumen fermentation. Huntington et al. (2001), Marini and Van Amburgh (2003), and Kohn et al. (2005) reported that PUN concentrations and urinary N excretion increased linearly with the amount of dietary protein as a result of the additional N supplied. Increased rumen ammonia N concentrations are also associated with natural protein s upplementation (DelCurto et al., 1990; Mathis et al., 2000; Loy et al., 2007), as feed protein degraded in the rumen is converted to ammonia N. Heifers consuming low quality grass hay had greater rumen ammonia concentrations when supplemented with DDG com pared to no supplemental protein (Loy et al. 2007). The degree to which ammonia N concentrations increase is dependent upon the rumen degradability of the feed protein. The addition of protein supplements to the diets of beef cattle consuming low quality forages will increase the N status of the animal, as exhibited through greater PUN and rumen ammonia concentrations, which will typically result in greater urinary N excretion.

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21 Non Protein Nitrogen Ruminant animals have the unique ability to utilize dieta ry NPN to support microbial metabolism and the production of microbial cell protein Urea is the most common source of NPN used as a N supplement for beef cattle. However, urea carries a risk of toxicity due to its high solubility within the rumen. Upon entering the rumen, microbial urease breaks down urea into ammonia and carbon dioxide. Ammonia from urea is rapidly available after consumption and absorbed across the rumen wall, which may result in rapid increases in blood ammonia N concentrations (Web b et al., 1972) Additionally, the presence of urea increases the pH of the rumen fluid. The greater pH favors the NH 3 form of ammonia, which is more readily absorbed across the rumen wall, in contrast to the ion form, NH 4 + Greater amounts of dietary u rea will cause large amounts of ammonia to be absorbed into the blood, which may result in death due to urea toxicity (Owens and Zinn, 1993). In order to avoid toxicity, it has been suggested that urea should supply no more than 15% of total dietary DIP w hen supplemented to cattle consuming low quality forage (Farmer et al., 2004b ). As a result of the risk of toxicity associated with urea, other sources of NPN have been examined that are not as rapidly solubilized. Biuret is not as soluble as urea, and th erefore, releases N at a slower rate within the rumen (Fonnesbeck et al, 1975). Biuret carries essentially no risk of toxicity as a result of its slow degradation rate; therefore, greater amounts of biuret may be fed compared to urea (Fonnesbeck et al 1 975). Animal performance Beef cattle consuming low protein diets usually exhibit an improvement in performance when supplemented with NPN compared to unsupplemented cattle Currier et al. (2004 a ) demonstrated that cows consuming low quality fescue straw a nd supplemented with urea or biuret were more likely t o maintain BW and BCS compared to cows receiving no supplemental

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22 DIP during the prepartum period. Brown and Adjei (2001) observed greater ADG for steers grazing low e when supplemented with molasses that contained urea, feather meal, or a combination of urea and feather meal compared to molasses alone. However, natural proteins may enhance cattle performance when used either in conjunction with or in place of NPN, pa rticularly for cattle with greater protein requirements such as gestating, lactating, or growing cattle. In these situations, NPN supplements may not provide adequate amounts of necessary amino acids to support maximum animal performance. Pregnancy rate and ADG were greater for heifers receiving molasses with urea supplements that also contained feather meal, catfish meal, or catfish oil compared to heifers receiving only molasses with urea (Pate et al., 1995). Additionally, ADG of steers increased by as much as 0.18 kg/d when sources of natural protein were included in the molasses urea supplements (Pate et al., 2005). Another experiment by Pate et al. (1990) reported that cow pregnancy rate was improved when cottonseed meal and urea were added to molas ses supplements, while cows offered molasses with urea were intermediate. Similar to natural protein supplements, NPN may performance. Forage intake Supplementation of DIP t hrough NPN sources has led to varying responses in voluntary forage DMI. Ammerman et al. (1972) c onducted three trials that examined the effect of natural protein and NPN supplementation on forage DMI in wethers offered ad libitum pangolagrass hay. Greate r hay DMI was observed when wethers were supplemented with urea and cottonseed me al compared to wethers that received no supplemental protein. Additionally, wethers consumed a greater amount of hay when offered a supplement of biuret with citrus pulp comp ared to citrus pulp alone or no supplement. No differences in hay DMI were observed in

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23 the third trial when urea or biuret was added to a SBM supplement; however, wethers supplemented with SBM alone or with urea or biuret consumed greater amounts of hay c ompared to wethers receiving no su pplemental protein. Currier et al. (2004 a) indicated that intake by wethers was not affected when offered daily or alternate day urea or biuret containing supplements compared to wethers receiving no supplemental DIP. Ho wever, Kostenbauder et al., (2007) indicated that steers consumed greater amounts of bahiagrass hay when urea was included in a molasses supplement compared to molasses alone. The effects of NPN supplementation have been difficult to predict, and are like ly affected to a large degree on the type of forage consumed and the type of supplement offered. Digestibility Supplemental NPN has bee n associated with increased diet digestibility, but conflicting results have been reported. Coleman and Barth (1977) dem onstrated that overal l DM digestibility was not affected when biuret was added to molasses or corn and citrus pulp supplements for yearling steers consuming pangolagrass hay. However, Kalm b acher et al. (1 995) reported that OM ADF, and NDF digestibilities decreased when urea was included in a supplement fed to steers con suming low quality bluestem hay, which was in contrast to greater digestibilities observed in steers receiving SBM supplements. Supplemental N has been associated with improved forage dige stibility, as low protein diets may limit the activity of fiber digesting microbes, and in turn, inhibit ruminal forage digestion (Kster et al., 1996). However, this does not always occur when NPN supplements are used. The effect of protein supplementat ion on forage digestibility may be dependent on the potential digestibility of the forage. Forages that have a greater potential for ruminal digestion may respond more positively to protein supplements (rskov and Grubb, 1978).

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24 Physiological responses The addition of NPN to the supplements of forage fed cattle has led to varying physiological responses. In a three year study by Brown and Adjei (2001), no differences were observed in steer grass pasture during the first two years of the experiment However, steer PUN concentration was greater when urea was added to a molasses supplement, with or without feather meal, during the third year. Plasma urea nitrogen concentrations responded diff erently during year three as a result of differences in forage quantity and forage protein. Dietary protein may have been in excess in relation to energy during the first two years as indicated by PUN concentrations above 10 mg/dL (Hammond et al., 1993). In year three, forage quantity and protein concentrations declined, resulting in a forage TDN:CP ratio of approximately 11, which created a greater potential for performance improvement through protein supplementation (Moore et al., 1999). Pate et al. (1 995) also reported greater PUN concentrations in steers and heifers supplemented with a molasses urea supplement compared to molasses supplements that substituted urea with natural proteins. When urea enters the rumen it is converted to ammonia. As a resu lt, rumen ammonia N concentrations typically increase when urea is included in the diet (Henning et al., 1993; Kim et al, 2007). Ammonia has a basic pH (Owens and Zinn, 1993), and therefore, dietary urea should cause an increase in rumen pH (Webb et al., 1972). The addition of urea to forage based diets oftentimes does not result in rumen pH changes in vivo (Kster et al., 2002; Bohnert et al., 2002c; Farmer et al., 2004b). Conversely, urea has caused an increase in pH and ammonia N concentrations in vit ro when innoculum was incubated with citrus pulp and urea (Kim et al., 2007).

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25 As the concentration of VFAs increases, the pH of rumen fluid should decrease; however, urea may only affect VFA concentrations when fed at very high levels (Kster et al., 2002) Furthermore, total VFA concentrations may not change as a result of urea addition. Instead, urea may shift the concentrations of individual VFAs, leaving total VFA concentrations, and therefore, rumen fluid pH, unaffected (Kster et al., 1997). Energ y Supplementation Performance of beef cattle consuming low quality forage may be improved through energy supplementation. However, energy supplements may also substitute voluntary forage intake, resulting in decreased forage DMI (Kunkle et al., 1999). Re ductions in forage DMI as a result of energy supplementation are typically associated with forage TDN:CP ratios of at least 7. This ratio indicates that forage CP is adequate, and there is a potential for improvement with additional dietary energy (Moore et al., 1999). The use of high starch energy supplements, such as corn, may have a negative impact on voluntary forage intake and digestibility (Galloway et al., 1993). Energy supplements that contain high levels of fermentable fiber, as opposed to starch may be a more desirable energy supplement to high forage diets (Richards et al., 2006). Soybean hulls ( SBH ) are a co product of the soybean processing industry, and are an energy supplement for forage fed beef cattle because they are high in fermentable fiber and low in starch. The feeding value of SBH is 15 30% greater than corn, which is high in starch, when used as a source of TDN for growing cattle on low quality forage diets (Garcs Ypez et al., 1997). Hales et al. (2007) indicated that SBH may be an economical supplement for grazing beef cattle by increasing the allowable stocking rate of pastures, and conserving forage during low availability without negatively affecting animal performance. Garcs Ypez et al. (1997) supplemented two levels of SBH to yearling steers and heifers consuming bermudagrass hay, and

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26 found that supplementation increased ADG compared to cattle receiving no supplement. Control cattle consumed greater amounts of hay compared those receiving SBH supplements; however, SBH substituted for only a portion of hay DMI, and total feed intake was still greater when SBH were fed. Dried distillers grains are a unique protein feed, in that they may also be considered a source of energy due to the high amount of fat and fermentable fi ber (Loy et al., 2007). Distillers grains are a co product of the corn derived ethanol industry. Ethanol production has been increasing dramatically over the last decade, and as a result, the supply of DDG has increased as well (Loy et al., 2005). The i ncreased demand for corn to produce ethanol has caused corn prices to rise. Therefore, producers that typically feed corn to their cattle have begun searching for more economical energy feeds. The ever increasing supply of corn co products has left the s upply of DDG relatively cheap compared to most protein feeds, and currently, DDG have been competitively priced as a source of energy rather than protein, which are usually more expensive (Schroeder, 2003). Increasing levels of supplemental DDG have resul ted in a positive linear response for ADG in growing steers grazing summer sandhill range (Morris et al., 2005) and in heifers offered ad libitum bromegrass hay (Morris et al., 2006). Theory of Nutrient Synchrony More than 30 years ago it was suggested tha t in order to maximize microbial protein synthesis, sources of N and carbohydrates should be selected which share similar rates of fermentation (Johnson, 1976). The concept of synchronizing the availability of energy and N has been hypothesized to enhance microbial production, and therefore, improve animal performance (Huber and Herrera Saldana, 1994). A synchronized diet would be one which provides energy and N at the same time and rate within the rumen, whereas an asynchronous diet does not. For exampl e, an as ynchronous diet would use urea as a supplement to l ow quality forage. Nitrogen

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27 from urea becomes available for use by the rumen microbes at a much faster rate compared to the availability of energy from low quality forage. As a result, peak N ava ilability occurs much sooner than peak energy availability The asynchronous peaks in energy and N may inhibit microbial production by not proving a continuous supply of nutrients Soybean meal is a source of protein that would provide a more synchronize d supply of N with low quality forage. In contrast, corn would provide energy from the degradation of starch at a rate similar to that of the release o f N from urea. A synchronized diet should theoretically increase microbial efficiency by presenting bot h energy and N to the rumen microbes at the same time. While some studies have reported improved N retention and microbial efficiency as a result of feeding supplements that are synchronized with low quality forage ( Matras et al., 1991; Richardson et al., 2003; Farmer et al., 2004a ), Henning et al (1993 ) concluded that microbial efficiency was not affected by diet synchrony in wethers consuming low quality wheat straw. Additionally, while Richardson et al. (2003) noted that diet synchronization improved th e efficiency of nutrient utilization, this did not equate to improvements in BW gain, forage DMI, or G:F. There are a number of ways to implement a synchronous diet for beef cattle. Nutrient synchrony may be as simple as providing energy and protein suppl ements every day as opposed to less frequent supplementation, such as every other day or three times per week. Forage diets may be further synchronized by selecting protein supplements that provide N at a similar rate as the availability of energy from fo rage. Feeding programs which provide protein supplements daily have sometimes resulted in improved animal performance (Collins and Pritchard, 1992; Beaty et al., 1994; Huston et al., 1999; Farmer et al., 2001 ) and increased forage intake ( Beaty et al., 199 4, Farmer et al., 2001;

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28 Farmer et al. 2004a) when compared to less frequent supplementation. Despite these improvements in animal performance, the differences are often very small. The increased labor costs associated with providing daily supplements are oftentimes not justified by the slight improvements in animal performance compared to programs which offer supplements less frequently. Furthermore, it has been suggested that producers who wish to implement alternate day supplementation programs should select protein supplements high in UIP (Collins and Pritchard, 1992). This provides a greater level of amino acids directly to the animal, and does not consistently result in decreased animal performance and intake compared to daily supplementation progra ms (Collins and Pritchard, 1992). However, Bohnert et al. (2002a) indicated that protein degradability or supplementation frequency did not affect the efficacy of supplement programs based on a lack of differences in DMI and microbial efficiency. Selectio n of feedstuffs with similar rates of energy and N release should theoretically lead to improved microbial production, and therefore, improved animal performance. However, this has rarely been proven in practice. Henning et al. (1993) did not observe dif ferences in microbial efficiency of wethers that received ruminal infusions of energy and N at synchronized rates of fermentation compared to asynchronous release rates. Kim et al. (1999) concluded that synchronized diets may be most effective when applie d to high concentrate diets which have a greater amount of rapidly digestible energy, rather than high forage diets which provide energy at a slower rate. Diet synchrony has resulted in improved rumen fermentation, exhibited by increased VFA concentration s in sheep consuming a low protein, high fiber diet (Puga et al., 2001); however, these results are typically not observed in forage fed beef cattle. Owens et al. (1980) examined a commercial, coated urea product and concluded that the slow release charact eristics eliminated ammonia toxicity risk and increased voluntary forage

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29 DMI compared to urea supplements in steers consuming ad libitum cottonseed hulls. A follow up study by Forero et al. (1980) measured the effects of the same slow release urea product compared to urea and SBM based natural protein in lactating cows grazing tallgrass range. At 1 hr after feeding, cows supplemented with urea had greater rumen ammonia concentrations compared to cows supplemented with slow release urea or natural protein; however, ammonia concentrations were not different after 4 hr. The slow release characteristics of the urea product did not improve cow performance compared to standard urea. Furthermore, cows receiving the urea supplements lost more BW and body conditi on compared to cows offered the SBM based natural protein supplement, indicating that urea in either form was not sufficient to meet the protein demands of lactating cows. The effects of diet synchronization on the rumen environment have been studied in o rder to determine how diet synchrony affects various fermentation characteristics. Bohnert et al. (2002c) offered DIP supplements daily, every third day, or every sixth day to steers consuming low quality meadow hay. On the day all steers received supple ments, rumen ammonia N concentrations increased as supplementation frequency decreased. Additionally, total VFA and butyrate increased as supplementation frequency decreased. However, when rumen fluid samples were obtained on the day only daily supplemen ts were offered, rumen ammonia N concentrations and total VFA decreased as supplementation frequency decreased. Additionally, rumen pH was greater when supplements were not offered daily. Farmer et al. (2004b) also observed differences in VFA concentrati ons as a result of supplementation frequency. On the day all steers were supplemented, steers consuming dormant tallgrass prairie hay and offered daily urea supplements had greater acetate concentrations and decreased propionate concentrations compared to steers offered urea on alternate days. This resulted in a greater

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30 acetate:propionate ratio for steers supplemented daily. However, there were no differences in acetate or propionate concentrations on the day only daily supplements were offered. Total V FA concentrations were not different on days when all steers were offered urea, but were greater in steers receiving daily urea supplements on days when alternate day steers did not receive urea. In both trials, these differences did not affect intake by steers; however, it is clear that synchronous diets cause the conditions within the rumen to remain relatively constant, while the rumen environment for cattle receiving asynchronous diets may change frequently. This is also supported by the findings of V alkeners et al. (2004), who offered energy and N supplements to Belgian Blue bulls either at the same time, or 12 or 24 hours apart. They concluded that synchronized diets did not affect rumen pH or ammonia N concentrations during a 48 hour period; howeve r, concentrations exhibited wide variation across the 2 d sampling period. Nutrient synchrony usually does not affect performance of forage fed cattle as a result of N recycling. Ruminants are able to maintain relatively constant levels of rumen ammonia N even when N intake is low. Any N that remains in the rumen which is not needed for microbial utilization will travel to the liver as blood ammonia, where it is stored as urea. When rumen ammonia N levels decline and additional ammonia is needed, urea travels through the blood as PUN from the liver to the rumen to replenish rumen ammonia N supplies (Owens and Zinn, 1993). This system of delivering necessary N to the rumen may eliminate the need for diet synchrony, as the ruminant has the ability to mai ntain adequate levels of ammonia N despite fluctuations in availability of protein from feed sources within the rumen. The concept of nutrient synchrony has been successfully applied to ruminant diets; however, synchrony has rarely affected performance o f beef cattle consuming low quality

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31 forage. Further research may help to determine the practical applications, if any, of nutrient synchrony in forage fed beef cattle.

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32 CHAPTER 3 UREA AND OPTIGEN II AS SOURCES OF DEGRADABLE INTAKE PROTEIN FOR MATURE BEEF COWS Introduction In Florida, cow calf producers commonly use bahiagrass ( Paspalum notatum ) as the main source of forage to maintain their beef cows. Bahiagrass general ly contains about 8% CP or less on a DM basis (NRC, 2000). Most cows are not capable of consuming enough low quality forage to satisfy their maintenance requirement for protein. Therefore, it is important for beef cattle producers to implement a protein supplementation strategy for their cows, particularly for cows and heifers that have additional protein requirements associated with gestation, lactation, and growth. Protein components may be classified as either degradable intake protein ( DIP ) or undegra dable intake protein ( UIP ). Supplementation of DIP has been shown to positively affect cattle performance, forage DMI, and forage digestibility (Sowell et al., 2003; Currier et al., 2004a). Urea may be used as a source of DIP (281% CP), which provides NP N to the rumen microbes without adding to the bulk density of the diet. The free space created in the diet can then be utilized to provide additional energy or other nutrients to meet or supplement cattle requirements. However, too much urea in the diet (>15% of total DIP) could lead to decreased performance compared with lower levels of urea supplementation ( Farmer et al., 2004b). The decrease in performance of cattle consuming low quality forages and high versus low levels of urea could be the result o f the asynchrony of ruminal ammonia and digestible energy in the overall diet. The release of N in the rumen from urea is near instantaneous, while the release of energy from low quality forages is not as readily available. Matching the slow release ener gy from forage with slow release N from a protein supplement may provide a more consistent supply of digestible nutrients in the rumen, avoiding sharp peaks of a single nutrient and

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33 improving diet utilization efficiency. Optigen II (Alltech, Inc., Nichola sville, KY) is a slow release N source. The delayed availability of N associated with this product was hypothesized to synchronize with the availability of energy from low quality forage, thereby increasing DMI, resulting in improved cow performance. Mate rials and Methods Animals and Diets All experimental protocols were approved by the University of Florida Institutional Animal Care and Use Committee (Protocol # E486) and were conducted at the University of Florida, Range Cattle Research and Education Cen ter, Ona. Twenty four non pregnant Brahman crossbred cows were blocked by BW (mean = 507.5 63 kg) and randomly assigned to one of three treatments. Cows were then randomly assigned to individual feeding pens outside with an overhead roof. Cows had ad libitum access to fresh water. Cows were offered ad libitum (110% of previous day intake) access to chopped (8 20 cm) bahiagrass hay (Table 3 1). Diets were presented to the cows at 0700 each morning. Treatments included: 1) Control ; 2) Urea ; 0.11 kg Urea; 3) Optigen ; 0.11 kg Optigen II. Cows were offered a basal supplement consisting of 0.91 kg of citrus pulp on an as fed basis, which was used as a carrier for the N supplement, and 0.15 kg of molasses as fed, which was used to bind the urea or Opti gen II supplement to the carrier. Supplement formulations contained 50 g of a vitamin mineral premix. One cow from the Control treatment and one cow from the Optigen II treatment were removed from the experiment and not replaced due to refusal to consu me the supplement. One cow on the Urea treatment died on d 3 from causes unrelated to the treatment, and was replaced on d 4.

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34 Sampling and Analysis Cows were fed for 56 d. Daily hay intake was recorded, and weekly means were calculated. Orts were collec ted daily and analyzed for DM content. Hay samples were obtained air oven for approximately 72 h. Bodyweight and BCS ( 1 =severely emaciated, 9=very obese; Wagner et al., 1988) were recorded on three sampling dates: March (d 0, initiation of the study), April (d 28) and May (d 56). Body condition scores were assigned by the same trained individual at each collection date. Prior to d 0, all cows were maintained in a single pen with ad libitum access to long stem hay and water. On d 0, full BW were obtained. On d 28 and 56, BW were measured approximately 3 h after the daily ration of hay and supplement were offered. Blood samples were obtained approximately 3 h pos t feeding via jugular venipuncture, collected in heparinized tubes, placed on ice and transported to the laboratory for further processing. Blood samples were centrifuged at 855 x g for 15 min at room temperature to obtain plasma, which was then frozen at 30C. Plasma samples were thawed at room temperature and filtered for analysis of plasma urea nitrogen ( PUN ) and plasma glucose concentrations. Concentrations of PUN and glucose were determined using a Technicon Autoanalyzer II (Technicon Instruments C orp., Chauncey, NY) The method used for PUN analysis was a modification of Coulombe and Favreau (1963) as described in Method #339 01 by Bran+Leubbe Industrial. The method used for plasma glucose analysis was a modification of Gochman and Schmitz (1972) as described in Method #339 19 by Bran+Leubbe Industrial. On each sampling date, rumen fluid samples were obtained via vacuum aspiration for analysis of pH and rumen ammonia N and VFA concentrations. After determination of rumen fluid pH (Denver Instrume nts, Denver, CO), 100 mL of fluid was acidified with 2 mL of 20% H 2 SO 4 (vol/vol), and samples were subsequently frozen at 30C. Samples were thawed at room

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35 temperature and filtered through four layers of cheese cloth for analysis of rumen ammonia N and V FA concentrations. Samples were centrifuged at 2,147 x g for 15 min at 4C. The supernatant was transferred through filter columns into high density polyethylene scintillation vials. Ammonia N concentration of rumen fluid was determined using an Alpkem Autoanalyzer (Alpkem Corporation, Clackamas, OR) using the method described by Kim et al. ( 2007b ). Volatile fatty acid concentrations were determined using a Hitachi HPLC (Hitachi, Tokyo, Japan) by the method described by Muck and Dickerson (1988). Twenty L of sample was obtained using a Hitachi autosampler (Hitachi, Tokyo, Japan) and injected into a Bio Rad Animex column (Bio Rad Laboratories, Hercules, CA). The mobile phase consisted of 0.015M H 2 SO 4 with a flow rate of 0.7 mL/min at 45C. Absorbance r eadings were detected at 210 nm using a Spectroflow UV detector (ABI Analytical Kratos Division, Ramsey, NJ). Data was collected using an LCI 100 Laboratory Computing Integrator (Perkin Elmer Corp., Norwalk, CT). Monthly hay and citrus pulp samples were c omposited for analysis of chemical composition (Table 3 1). Hay samples were analyzed by near infrared spectroscopy by a commercial laboratory (Dairy One, Ithaca, NY). Monthly samples of citrus pulp were analyzed by the same laboratory. Dry matter was d etermined by drying samples for 2 h at 135C (procedure 930.15; AOAC, 2000). Concentrations of ADF and NDF were determined using an Ankom 200 Fiber Analyzer (Ankom Technology, Macedon, NY) by the methods described by Van Soest et al. (1991), and crude prot ein was determined using the Kjeldahl method (procedure 984.13; AOAC, 2000). Statistical Analysis The experiment was designed as a completely randomized design, with N supplementation treatment as the f ixed effect (Littell et al., 200 6), and cow within tr eatment as the random effect.

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36 Cows were fed individually; therefore, cow was the experimental unit. Data were analyzed using the Mixed procedure of SAS v9.1 (2002, SAS Inst., Inc., Cary, NC). Means were calculated using least squares means, and means we re separated using the P diff option wh en the overall F value was <0.10 Results and Discussion Cow Performance At the initiation of the trial there were no differences ( P =0.95) in cow BW (mean = 508 23.1 kg) among treatments (Table 3 2). Additionally, on d 28 and 56 mean cow BW did not differ ( P =0.92, 0.78, respectively) among treatments. During the first 28 d, BW change did not differ ( P =0.86; mean = 9.0 kg); however, from d 28 to 56 BW change of cows supplemented with Optigen tended to be greater ( P <0.10 ) than that of cows fed the control diet Likewise, BW change of urea supplemented cows was 31.5 kg greater ( P <0.05) compared to the cows on the Control treatment. There was no difference ( P >0.10) in BW change between cows offered Optigen or urea du ring this period. Cumulative BW change from d 0 to 56 tended ( P =0.11) to be affected by treatment; BW change of cows consuming Urea was 27.4 kg greater ( P <0.05) compared to cows consuming the Control diet, and BW change of cows supplemented with Optigen w as 23.1 kg greater ( P <0.10) compared to cows consuming the Control diet. There were no differences ( P >0.10) between Optigen and Urea treatments in overall BW change. The TDN:CP ratio of the bahiagrass hay was 6.63. Ratios below 7 indicate that forage CP and energy concentrations are balanced (Moore et al., 1999). While there was likely a desirable ratio of energy to protein in the bahiagrass hay, the NRC (2001) Level 1 model indicated that the energy and protein requirements of the cows offered the Contr ol diet were not met. The addition of DIP satisfied the protein requirements of the cows on urea and Optigen treatments, but dietary energy was still deficient. This may explain the tendency for cows receiving supplemental DIP

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37 to have positive cumulative BW changes compared to cows receiving no supplemental DIP. In a 275 d study, Del Curto et al. (1990) observed linear increases in BW with increasing levels of protein supplementation for mature cows consuming low quality forage. However, BW change was n ot different after 28 d, and cumulative BW change was not different until d 84. Additionally, it has been demonstrated that cows consuming low quality forage respond more to natural sources of protein compared to NPN supplements (Farmer et al., 2004b). T he relatively short duration of DIP supplementation was likely not sufficient to fully demonstrate the effects of urea and Optigen II on BW changes of mature beef cows in a practical production system. Forero et al. (1980) offered urea, slow release urea and SBM supplements to cows consuming low quality forage for 92 d and concluded that slow release urea resulted in less BW loss compared to urea. However, natural protein from SBM maximized cow performance. This may indicate that urea products that syn chronize the availability of N with the availability of energy from low quality forage may enhance cattle performance. However, when economical, sources of natural protein may have more practical applications, particularly for cattle with greater protein requirements, as low quality forage and urea may not be sufficient to meet metabolizable protein requirements. Cow BCS was not different ( P =0.61, 0.45, 0.94) on any of the three sampling dates (Table 3 2). Additionally, BCS change was not different among treatments from d 0 to 28 ( P =0.98), d 28 to 56 ( P =0.37), or from d 0 to 56 ( P =0.39). The NRC (2001) Level 1 model predicted that the Control diet would decrease cow BCS by one unit in 78 d, and cows receiving supplemental DIP would decrease one BCS in 75 d. The duration of the experiment was 56 d, which was likely not adequate time to observe the effects of diet on BCS. These results are consistent with those reported by Dhuyvetter et al. in 1993, in which cows were supplemented with either 75%

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38 or 50% D IP (% of CP). Body condition score was observed from March 1991 (before calving) to May 1991 (before breeding). During this period, the lactating cows did not exhibit BCS change as a result of postpartum protein supplementation treatment. Based on these results, it can be concluded that cows that did not respond to DIP supplementation during lactation would also not experience changes in BCS during a two month period as a result of protein supplementation. Mean weekly hay DMI was not different ( P >0.45) d uring any of the eight wk when expressed either as kg/d or as a % of BW (Table 3 3, not all data presented). From wk 4 to 8, cows supplemented with urea increased their mean hay DMI by nearly 2 kg/d more ( P =0.03) compared to cows offered the Control diet. This was equivalent to an increase of 0.56% BW for cows offered urea, compared to an increase of 0.22% of BW for cows offered the Control diet ( P =0.04). Changes in hay consumption among treatments were not observed from wk 1 to 4 ( P =0.31, 0.37) or acros s the entire experiment from wk 1 to 8 ( P =0.90, 0.86) when expressed as kg/d or as a % of BW. Conflicting research has reported that DIP supplementation stimulates an increase in forage intake in ruminants (Campling et al., 1962), whereas other reports ha ve not observed an increase in forage intake as a result of NPN supplementation (Kster et al., 2002; Currier, 2004a; Farmer, 2004b). As previously indicated, it is likely that the energy requirements of the cows in the current study were not met. Cattle will consume feed to meet their energy amounts of hay to satisfy their energy requirements (Allen, 1996). Therefore, the reported voluntary hay intake values may reflect the maximum amount of hay the cows were able to consume, rather than the maximum amount of hay the cows chose to consume.

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39 Physiological Response Plasma glucose concentrations did not differ ( P >0.45) among treatments on any of the three sampli ng dates (Table 3 4) Plasma glucose concentration was likely related to hay intake as energy i ntake has been shown to affect plasma glucose concentration, independent of energy source (Schmidt and Keith, 1983). No differences were observed in hay DMI o n any of the three dates on which plasma glucose concentrations were measured, which may have contributed to the lack of differences observed on d 0, 28, and 56. Prior to the initiation of NPN supplementation on d 0, PUN concentration was not different ( P = 0.16) among treatments (Table 3 4 ). On d 28, cows supplemented with either urea or Optigen (mean = 16.39 mg/dL) had greater ( P <0.001) PUN concentrations compared to cows receiving no supplemental DIP (1.91 mg/dL) and PUN concentrations in the blood of co ws consuming urea tended ( P =0.10) to be gre ater than that of cows consuming Optigen. Additionally, o n d 56 PUN concentrations of the cows on the Control treatment were 11.2 mg/dL less ( P <0.001) than cows supplemented with Urea or Optigen. There were no differences ( P =0.15) between Op tigen and Urea treatment s on d 56. While the results of this study indicate that synchronized NPN sources may result in decreased PUN concentrations, Sinclair et al. (2000) did not observe any differences in PUN of heifers o ffered synchronized versus asynchronized supplements to a basal diet of barley straw. Plasma urea nitrogen concentrations of cows consuming urea likely tended to be greater than that of cows consuming Optigen on d 28 as a result of the controlled release p roperties of Optigen II. When urea is consumed, it becomes rapidly available to the rumen microbes as ammonia N as a result of its high solubility (Currier et al., 2004a). Plasma was collected approximately 3 h post feeding. During this time, it is lik ely that most of the urea would have been solubilized ( Owens et al., 1980 ). Not all of this ammonia N may be immediately utilized

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40 by the microbes, and is therefore recycled out of the rumen, with some appearin g in the plasma as urea N Optigen II, howev er, is not as rapidly soluble, thereby releasing ammonia N over an extended period of time within the rumen. Optigen II is not completely degraded until nearly 16 h post feeding (Siciliano Jones and Downer, 2005). As a result, a smaller proportion of am monia N would likely have been recycled into the blood stream at the time of collection, resulting in lower PUN concentrations for cows consuming Optigen II compared to urea. Hammond et al. (1993) indicated that PUN concentrations of beef cattle maintaine d on subtropical forages should be between 8 12 mg/dL. Concentrations below 8 mg/dL indicate that protein is deficient, while concentrations above 12 mg/dL indicate that additional dietary energy is necessary. The cows on the Control diet had very low PUN concentrations throughout the experiment; therefore, additional dietary protein would likely have improved cow performance. On d 28 and 56, cows offered both urea and Optigen had PUN concentrations greater than 12 mg/dL. Performance of these cows may have been improved with additional dietary energy. These principles are consistent with the results of the NRC (2001) Level 1 model. The only treatment that indicated a need for additional protein was the Control treatment. Urea and Optigen supplementa tion provided adequate metabolizable protein; however, energy was still deficient. These results indicate that Urea and Optigen were equally effective at increasing the protein status of the cows to adequate levels; however, additional energy supplementat ion may have been necessary to maximize cow performance. The pH of aspirated rumen fluid was not different ( P =0.29) on d 0 (Table 3 5). On d 28, treatment tended ( P =0.07) to affect rumen pH. Cows on the Control diet had greater ( P <0.05) ruminal fluid pH compared to cows offered Optigen, while the Urea treatment was intermediate. There were no treatment differences ( P >0.10) in cow rumen pH on d 56. Overall mean rumen

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41 fluid pH tended ( P =0.09) to be affected by treatment. Mean rumen pH of Optigen suppleme nted cows was 7.64 compared to 7.79 for cows on the Control treatment ( P <0.05); however, neither Optigen supplemented nor Control supplemented cows differed from urea supplemented cows ( P >0.10), which had an overall mean pH of 7.70. In the rumen, urea is c onverted to ammonia, which is basic. Therefore, it is generally accepted that urea should increase the pH of the rumen (Webb et al., 1972; Owens and Zinn 1993), which is contrast to the results observed in this trial. Furthermore, rumen fluid pH should b e inversely related to VFA concentrations (Kster et al., 2002). Both rumen pH and total VFA concentrations tended to decrease with NPN supplementation, which is also in contrast to the expected results. Kim et al. (2007) observed greater pH values in vi tro when rumen fluid was incubated with citrus pulp and urea compared to citrus pulp alone. Many studies have reported that urea as a supplement to low quality forage has no effect on rumen pH (Kster et al., 1997; Bohnert et al., 2002c; Currier et al., 2 004b). It should be noted that in the current study, saliva contamination caused reported pH values to be about one pH unit greater than would be expected as a result of the process by which the rumen fluid was obtained. It is likely that saliva contamin ation buffered the rumen fluid samples such that accurate rumen pH values were not recorded. On d 0, there were no differences ( P =0.65) among treatments for rumen ammonia N concentrations (Table 3 5 ). On d 28, ammonia N concentrations were greater ( P =0.00 3 ) for cows supplemented with NPN. Rumen amm onia N concentration of cows offered the Control treatment was 47% less ( P <0.01 ) than that of cows supplemented with Urea or Optigen. However, rumen ammonia N concentration was not different ( P =0.97) between Ur ea or Optigen supplemented cows on d 28. On d 56 cows receiving no supplemental DIP again ha d the lowest

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42 ( P <0.001) ammonia N concentrations which was 31% that of cows offered Optigen ( P <0.01), while c ows supplemented with Urea exhibited rumen ammonia N c oncentrations that were nearly 4 times greater ( P <0.01) compared to the Control treatment. Rumen ammonia N concentration tended ( P <0.10) to be about 10 mg/dL greater for cows offered urea compared to Optigen on d 56. Forero et al. (1980) observed grater r umen ammonia N concentrations in cows offered urea compared to a slow release urea product as a supplement for low quality tallgrass range one hour after feeding. However, 4 hours post feeding, rumen ammonia N concentrations were not different. In the pr esent study, rumen fluid samples were obtained within 3 hours after presenting supplements to the cows. It is possible that differences between Optigen and urea supplemented cows were not observed during this time period, as peak rumen ammonia N concentra tions from urea had likely occurred prior to completion of sampling. Rumen ammonia N concentrations increased in all cows from d 0 through the completion of the experiment. This was likely the result of greater daily hay intakes, and the inclusion of mola sses and citrus pulp supplements, with or without additional DIP. The increased rumen ammonia N concentrations for NPN supplemented cows compared to the Control treatment was a result of the additional DIP included in the supplements. Supplying additiona l N in the rumen environment provided a greater amount of N substrate to be converted to ammonia N. The tendency for rumen ammonia N concentration s to be greater for cows supplemented with urea compared to Optigen on d 56 may have been a result of the rate of N release. Webb et al. (1972) found that peak rumen ammonia N concentrations occurred less than 2 h after consumption of urea. Also, C urrier et al. (2004b) observed that rumen ammonia N concentrations of beef steers consuming low quality forage and o ffered daily urea supplements

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43 peaked at 3 h after consumption. Rumen fluid samples were obtained approximately 3 h post feeding; therefore, it is likely that peak rumen N concentrations were observed for the cows on the Urea treatment, as all of the urea should have been degraded within this amount of time. However, due to the slower rate of degradation associated with Optigen II compared to urea, peak rumen ammonia N concentration of cows consuming Optigen would not have been observed within this 3 h ti me period. As a result, rumen ammonia N concentrations of Optigen supplemented cows were lower compared to cows consuming urea. The rumen ammonia N concentrations observed in cows offered Urea and Optigen were much greater compared to other values report ed for forage fed beef cattle (Beck et al., 1992; Henning et al., 1993; Bohnert et al., 2002c; Valkeners et al., 2006). This was likely a result of the amount of NPN offered in the supplement. It is recommended that urea should contribute no more than 15 % of total dietary DIP (Farmer et al., 2004b). Based on average hay intake, cows on the Urea and Optigen treatments were consuming about 30% of their total DIP from urea. Toxicity was likely not a problem, as cattle have been shown to exhibit rumen ammon ia N concentrations as great as 129 mg/dL without showing signs of ammonia toxicity (Webb et al., 1972). Additionally, cows were fed about 97 mg N/kg BW from urea. In the toxicity study by Webb et al. (1972), the first animal to exhibit toxicity signs wa s receiving 150 mg N/kg BW from urea. Another animal was safely fed as much as 350 mg N/kg BW. The levels of NPN supplementation were likely much greater than required to meet the able to convert all of the N supplied by the NPN supplements to microbial protein, as the overall diet was not supplying adequate energy. As a result, the cows retained a large amount of N both in the rumen as ammonia N and in the blood as PUN.

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44 Total VFA concentrations were not different among treatments on d 0 or 28 ( P 3 5 ). Additionally, there were no differences ( P in concentrations of acetate on d 0 or 28 Mean acetate:propionate ratio was 2.93 across the entire experiment, but was not different among treatments on d 0, 28, or 56 ( P ). On d 0 treatment type tended to affect concentrations of propionate ( P =0.10) and butyrate ( P =0.08). Initial propionate concentrations were more than 4 m M / L greater for cows on the Control treatment compared to cows offered Urea ( P <0.05), with cows consuming Op tigen being intermediate. Initial butyrate concentrations were also greatest for the Control treatment, which was nearly 2 m M /L greater ( P <0.053) than cows on the Optigen treatment, with Urea supplemented cows being intermediate. While there were differe nces in these individual VFAs on d 0, when expressed as a percentage of total VFAs (data not shown), no treatment differences were observed ( P ( P =0.11) to affect both acetate and total VFA concentrations. Cows on the Cont rol diet had the greatest concentrations, while cows offered urea had the lowest concentrations of total VFAs and acetate; Optigen supplemented cows were intermediate. On d 56, butyrate concentrations were greatest ( P =0.04) for cows offered the Control di et, and lowest for cows offered. Cows supplemented with Optigen had intermediate levels of butyric acid and were not different from the other two treatments ( P <0.10). The differences in butyric acid concentrations were small, and did not occur consistent ly; therefore, it is difficult to determine how DIP supplementation may have affected rumen VFA concentrations. Both butyrate and acetate are precursors to acetyl CoA; therefore, a decrease in butyrate could be associated with an increase in acetate (B ohn ert et al., 2002a). While there were no differences in acetate, the numerical trends were similar to butyrate concentrations, with the cows consuming the Control diet having the greatest concentrations, followed by Optigen, then cows supplemented with ure a. Currier et al. (2004b)

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45 did not observe any differences in VFA concentrations as a result of supplementing urea or biuret to steers consuming ad libitum low quality fescue straw. The concentrations of VFAs for the cows in this study were similar to in vitro values observed by Kim et al. ( 2007a) where fermentation patterns of citrus pulp and urea were observed. It is not likely that the level of DIP supplementation in this study had a noteworthy effect on ruminal fermentation characteristics, and theref ore, the small differences observed are unlikely biologically significant. Implications Overall cow performance was generally not affected by additional DIP supplementation. The basal diets across all treatments likely did not meet the energy or protein r equirements of non lactating cows. The tendencies for DIP treatment to affect overall BW change may indicate that in the long term, DIP supplementation would be necessary to maintain BW of mature cows consuming a diet of bahiagrass hay with a citrus pulp supplement. It is unlikely that the rate of the DIP degradation within the rumen will affect cow performance.

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46 Table 3 1. Composition of feedstuffs fed to mature cows. Bahiagrass hay Citrus Pulp DM, % 93.7 86.4 % of DM OM 92.3 93.4 a CP 7.5 7 .1 DIP, % CP 52.7 41.6 a NDF 72.8 24.2 ADF 44.3 21.0 TDN 49.7 68.7 a NRC (2000) Tabular values. Table 3 2. Effect of supplemental NPN source on cow bodyweight (BW) and body condition score (BCS). Treatment a Item Control Urea Optigen SE M b P value BW, kg d 0 505 504 514 23.11 0.95 d 28 519 509 521 23.92 0.92 d 56 497 517 517 24.22 0.78 BW change, kg d 0 28 9.2 5.1 12.8 10.24 0.86 d 28 56 c 22.7 8.8 3.6 7.39 0.02 d 0 56 c 13.5 13.9 9.2 9.40 0.11 BCS d d 0 5.12 5.12 5.00 0.15 0.61 d 28 5.50 5.44 5.21 0.17 0.45 d 56 5.29 5.19 5.21 0.20 0.94 BCS change d 0 28 0.29 0.25 0.29 0.15 0.98 d 28 56 0.21 0.25 0.00 0.14 0.37 d 0 56 0.07 0.00 0.29 0.15 0.39 a Least square means; Tre atment: Control, No supplemental NPN; Urea, 0.11 kg rapid release NPN from urea; Optigen, 0.11 kg controlled release NPN from Optigen II. b Standard error of the mean, n=22. c Control vs. Urea ( P <0.05); Control vs. Optigen ( P <0.10); Urea vs. Optigen ( P >0. 10). d Body condition score, 1=severely emaciated, 9=very obese.

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47 Table 3 3. Effect of supplemental NPN source on hay dry matter intake (DMI) of mature cows. Treatment a Item Control Urea Optigen SEM b P value DMI, kg/d Wk 1 5.49 5.55 5.44 0. 45 0.99 Wk 4 9.13 7.92 8.34 0.91 0.45 Wk 8 10.38 10.77 10.09 1.08 0.90 Mean (Wk 1 8) 8.65 8.52 8.29 0.72 0.94 Wk 1 4 Change 4.01 2.37 2.90 0.77 0.31 Wk 4 8 Change c 0.88 2.85 1.75 0.49 0.03 Wk 1 8 Change 4.98 5.22 4.65 0.90 0.90 DM I, %BW Wk 1 1.06 1.06 1.08 0.07 0.98 Wk 4 1.83 1.54 1.60 0.17 0.47 Wk 8 2.04 2.10 1.95 0.21 0.87 Mean (Wk 1 8) 1.69 1.65 1.59 0.13 0.86 Wk 1 4 Change 0.77 0.46 0.54 0.16 0.37 Wk 4 8 Change c 0.22 0.56 0.34 0.10 0.04 Wk 1 8 Change 0 .98 1.02 0.88 0.19 0.86 a Least square means; Treatment: Control, No supplemental NPN; Urea, 0.11 kg rapid release NPN from urea; Optigen, 0.11 kg controlled release NPN from Optigen II. b Standard error of the mean, n=22. c Control vs. Urea ( P =0.01); Co ntrol vs. Optigen ( P P Table 3 4. Effect of supplemental NPN source on plasma concentrations of glucose and urea nitrogen of mature cows. Treatment a Item Control Urea Optigen SEM b P value Glucose, mg/dL d 0 84.66 87.71 85.63 5.3 9 0.92 d 28 77.88 78.73 75.24 5.12 0.88 d 56 84.92 82.26 74.06 6.19 0.45 PUN c mg/dL d 0 1.15 1.27 2.17 0.40 0.16 d 28 d 1.91 17.02 15.75 0.54 <0.001 d 56 e 1.61 13.44 12.23 0.59 <0.001 a Least square means; Treatment: Control, N o supplemental NPN; Urea, 0.11 kg rapid release NPN from urea; Optigen, 0.11 kg controlled release NPN from Optigen II. b Standard error of the mean, n=22. c Plasma urea nitrogen. d Control vs. Urea ( P <0.001); Control vs. Optigen ( P <0.001); Urea vs. Optig en ( P =0.10). e Control vs. Urea ( P <0.001); Control vs. Optigen ( P <0.001); Urea vs. Optigen ( P =0.15).

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48 Table 3 5. Effect of supplemental NPN source on ruminal fluid pH, ammonia N, and total VFA concentration. Treatment a Item Control Urea Optigen SEM b P value pH d 0 8.09 7.97 7.86 0.10 0.29 d 28 c 7.67 7.50 7.36 0.09 0.07 d 56 7.55 7.67 7.59 0.06 0.42 Mean c 7.79 7.70 7.64 0.05 0.09 Ammonia, mg/dL d 0 8.96 8.46 9.69 0.98 0.65 d 28 d 35.02 74.41 74.78 8.58 0.003 d 5 6 e 21.36 83.75 73.31 5.53 <0.001 Total VFA, m M /L d 0 91.12 81.95 76.83 4.75 0.12 d 28 98.87 95.08 98.57 6.35 0.87 d 56 f 103.55 89.94 91.86 4.74 0.11 Individual VFA, m M /L Acetate, m M /L d 0 59.09 55.22 50.65 2. 69 0.14 d 28 63.22 60.85 61.81 3.48 0.87 d 56 f 66.08 58.45 59.09 2.75 0.11 Propionate, m M /L d 0 f 21.09 16.42 17.17 1.54 0.10 d 28 22.89 22.02 22.96 1.80 0.90 d 56 23.16 20.61 20.98 1.56 0.46 Butyrate, m M /L d 0 c 9.35 8.22 7.60 0.54 0.08 d 28 10.69 9.63 11.23 1.18 0.58 d 56 f 11.05 8.33 9.84 0.72 0.04 Acetate:Propionate d 0 2.82 3.63 3.00 0.34 0.24 d 28 2.80 2.79 2.71 0.10 0.77 d 56 2.87 2.88 2.86 0.11 0.99 a Least squ are means; Treatment: Control, No supplemental NPN; Urea, 0.11 kg rapid release NPN from urea; Optigen, 0.11 kg controlled release NPN from Optigen II. b Standard error of the mean, n=22. c Control vs. Urea ( P >0.10); Control vs. Optigen ( P <0.05); Urea vs. Optigen ( P >0.10). d Control vs. Urea ( P <0.01); Control vs. Optigen ( P <0.01); Urea vs. Optigen ( P >0.10). e Control vs. Urea ( P <0.01); Control vs. Optigen ( P <0.01); Urea vs. Optigen ( P <0.10). f Control vs. Urea ( P <0.05); Control vs. Optigen ( P >0.10); Urea v s. Optigen ( P >0.10).

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49 CHAPTER 4 EVALUATION OF DRIED DISTILLERS GRAINS AND SOYBEAN HULLS AS SUPPLEMENTS FOR GROWING BEEF STEERS CONSUMING BAHIAGRASS HAY Introduction Low quality tropical and subtropical grass forages are often deficient in CP relative to the protein requirements of many classes of cattle. Therefore, cattle with greater protein requirements, such as growing cattle, will require additional protein supplementation to meet the nutritional demands associated with growth when maintained on a high forage diet. Dried di stillers grains ( DDG ) are a co product of the corn derived ethanol fuel industry. As ethanol fuel production continues to increase in the United States, DDG will become more available to livestock producers for animal consumption. Dried distiller grains a re high in CP but relatively low in degradable intake protein ( DIP ; 31.6% CP, 27.9% DIP as a % CP). Soybean hulls ( SBH ) are another co product which are relatively low in total DIP (12.6% CP, 58% DIP, as a % CP). For growing cattle a small amount of DIP may optimize performance when added to co product supplements. Optigen II (Alltech, Inc., Nicholasville, KY) is a urea product which has slow release properties that should result in N availability from urea that is better synchronized with the energy av ailability provided by fermentable forage. In Trial One, the Optigen II product was hypothesized to be a beneficial addition to DDG and SBH supplements by providing supplemental DIP. Optigen II is 100% DIP, which provides ammonia to the rumen microbes. In Trial Two, greater levels of supplementation were hypothesized to further enhance animal performance. Combinations of DDG and SBH were fed to determine practical feeding applications of these two co products.

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50 Materials and Methods Animals and Diets T rial one All experimental protocols were approved by the University of Florida Institutional Animal Care and Use Committee (Protocol # E728) and were conducted at the University of Florida Beef Research Unit, Gainesville. Fifty six Angus steers were block ed by BW (mean = 247 26 kg) and randomly assigned to one of seven pens and one of four treatments. Treatments included: 1) DDG (1.19 kg of DM); 2) DDG+Opt (1.19 kg of DDG, 45.5 g Optigen II); 3) SBH (2.63 kg of DM); 4) SBH+Opt (2.63 kg of SBH, 45.5 g O ptigen II). Basal supplements (DDG and SBH) were formulated to be isonitrogenous (0.36 kg CP); the addition of Optigen II provided 45.5 g of supplemental DIP. Steers were offered basal supplements daily beginning five d prior to the initiation of the e xperiment. Bahiagrass hay was offered to each pen, ad libitum, as large round bales. Fresh bales were offered each week, and each bale was weighed and core sampled for analysis of chemical composition. Steers were individually supplemented at approximat ely 0700 via a Calan gate system (American Calan, Northwood, NH). Approximately 57 g of a vitamin/mineral supplement was included in the daily supplements (composition: 20% NaCl, 13% Ca, 6% P, 1% Mg, 0.95% Zn, 0.8% K, 0.4% Fe, 0.4% S, 0.22% Mn, 0.2% Cu, 0 .08% F, 0.02% Co, 0.018% I, 0.005% Se, 100,000 IU/lb Vit. A, 20,000 IU/lb Vit. D 3 ). One steer on the SBH+Opt treatment incurred a shoulder injury on d 21, and was unable to comfortably use the Calan gate. This steer was replaced on d 22 with a steer of s imilar BW that had been supplemented with 2.63 kg SBH per day. The replacement steer began consuming the SBH+Opt treatment on d 22.

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51 Trial two The same 56 Angus steers (mean BW = 270 26 kg) utilized in Trial One were also utilized in Trial Two. Steers r emained in the pens to which they had previously been assigned. Within pen, steers were blocked by BW and randomly assigned to one of four isonitrogenous (2.32 kg TDN) treatments: 1) DDG (2.8 kg of DM); 2) DDG/SBH (1.93 kg DDG, 0.98 kg SBH); 3) SBH/DDG (0 .96 kg DDG, 2.05 kg SBH); 4) SBH (3.12 kg of DM). All steers were fed approximately 2.7 kg of SBH for five d prior to the initiation of the trial. Supplement treatments began on d 0 after sampling. Bahiagrass hay was offered to each pen, ad libitum, as large round bales. Fresh bales were offered each week, and each bale was weighed and core sampled for analysis of chemical composition. Steers were individually supplemented at approximately 0700 via a Calan Gate system (American Calan). Approximately 5 7 g of the vitamin/mineral supplement utilized in Trial One was included in the daily supplements. Sampling and Analysis During both trials, steers were fed for 42 d. Unshrunk BW were taken on two consecutive days at the initiation (d 1, 0) and terminati on of the trial (d 42, 43). Interim BW were obtained on d 14 and 28. The two d mean of BW was utilized to determine initial and final BW and to determine BW gain. In Trial One, BW measurements, blood, and urine samples were obtained approximately two h after supplements were offered. In Trial Two, BW measurements and blood samples were obtained prior to offering daily supplements. All blood samples were obtained via jugular venipuncture, collected into heparinized tubes, placed on ice, and transported to the laboratory for further processing. Blood samples were centrifuged at 3,565 x g for 15 min at 4C to obtain plasma, which was then frozen at 30C. Plasma was thawed at room temperature for analysis of plasma urea nitrogen ( PUN ) and plasma glucose concentrations. Plasma urea nitrogen concentrations were determined using an enzymatic urea N kit (Procedure

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52 No. 2050, Stanbio Laboratory, Boerne, TX). Absorbance readings were recorded at 600 nm using a Jasco UV/VIS Spectrophotometer (JASCO Corp., Tokyo Japan) Plasma glucose concentrations were determined using an enzymatic glucose kit (Autokit Glucose, Wako Diagnostics, Richmond, VA) with a modified procedure. In a 96 well flat bottomed plate, 300 L of working solution and 2.5 L of blanks, standa rds, and samples were added to each well, and the plate was incubated at 37C for five min in a Lab Line Orbit Environ Shaker (Lab Line Instruments, Melrose, CA) at 50 rpm. Absorbance readings of the samples were recorded at 505 nm using a SpectraMax 340 PC plate reader (Molecular Devices, Sunnyvale, CA) On each of the sampling dates of Trial One, spot urine samples were obtained from steers into disposable plastic bags. Urine was then transferred into 125 mL polyethylene storage containers, placed on ic e and transported to the laboratory. Urine was acidified to a pH < 3.0 using 20% H 2 SO 4 (vol/vol) and frozen for later analysis. Urine was thawed at room temperature, and creatinine concentrations were determined using a quantitative colorimetric procedur e (Procedure No. 0400, Stanbio Laboratory, Boerne, TX). Absorbance readings of the samples were recorded at 520 nm using a Jasco UV/VIS spectrophotometer (JASCO Corp.). Creatinine concentrations were used to determine total daily urine output based on th e principle that cattle excrete 883 mol of creatinine (kg BW 0.75 ) 1 d 1 ( Chen et al. 1992 ). Urine N concentrations were determined using a modified Kjeldahl block digestion: 10 mL of urine, six hollow boiling beads, approximately six g of a CuSO 4 K 2 SO 4 catalyst, and 20 mL of H 2 SO 4 were added to a 250 mL digestion tube. Twelve mL of 30% H 2 O 2 was slowly added to each tube, and samples were heated to approximately 400C. Glass condensers were placed on each tube when a white steam was observed, and sa mples were heated for 45 min. When cool, tubes were brought to volume with deionized water, and aliquots of approximately 20 mL were transferred through filter

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53 funnels into high density polyethylene scintillation vials. Percent N was determined using an Alpkem Autoanalyzer (Alpkem Corporation, Clackamas, OR). During both trials, weekly hay samples were collected from each pen and composited for analysis of chemical composition (Table 4 1). Samples were analyzed by near infrared spectroscopy ( NIRS ) by a c ommercial laboratory (Dairy One, Ithaca, NY). Weekly samples of DDG and SBH were analyzed by NIRS and wet chemistry, respectively. In vitro DM disappearance ( IVD MD ) of DDG and SBH samples was determined by the procedure of Tilley and Terry (1963), as mod ified by Marten and Barnes (1980) and filtration on filter paper. Inoculum for IVDMD was obtained from a ruminally fistulated cow fed ad libitum coastal bermudagrass ( Cynodon dactylon ) hay and 900 g/d of soybean meal, and strained through four layers of c heesecloth. The IVDMD of the hay samples were determined by NIRS. Hay and supplement TDN concentrations were determined using the equation (Fike et al., 2002): %TDN = [(% IVDMD 0.59) + 32.2] OM concentration. Because hay was fed as large round bales, mean daily hay DMI was calculated using the NRC ( 2000 ) equation: SBW = 13.91 RE 0.9116 EQSBW 0.6837 where: SBW = shrunk body weight RE = retained energy EQSBW = equivalent shrunk body weight, assuming a 4% shrink, and that RE is equal to net energy fo r gain (NE g ). Statistical Analysis Both experiments were designed as a completely randomized design, with supplement treatment as the fixed effect (Littell et al., 2006 ), and steer within treatment as the random effect.

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54 Steers were supplemented individual ly; therefore, steer was considered the experimental unit. Data were analyzed using the Mixed procedure of SAS v9.1 (2002, SAS Inst., Inc., Cary, NC). Means were calculated using least squares means, and means were separated using the P diff option when the overall F value was <0.05. Results and Discussion Trial One Steer performance At the initiation of the trial, steer BW averaged 247 kg (Table 4 2 ), with no differences ( P =0.97) among treatments. There were no differences in steer BW on d 14, 28, or 42 ( P =1.00, 0.86, 0.97). Additionally, no differences were observed in ADG during any two week sampling period, or across the entire experiment ( P The changes observed in steer BW from d 0 to 14 were approximately 2.4 times greater compared to the pe riod between d 14 and 28. The dramatic decline in ADG between the first two collection periods was likely due to compensatory gain observed during the first 14 d. Two wk prior to the initiation of the trial, steers consumed a restricted diet consisting o f only limited amounts of a grain based feed with molasses. The purpose of th is diet was to induce hunger to the study, when a majority of the steers had l earned to use their assigned gates, round bales of hay were placed in each pen, and steers were offered their basal supplements at 0700. All steers were willingly consuming from their assigned gates by d 0. During the two wk training period, steer BW gai n was minimal, with some steers losing BW. The ADG of all steers was 0.09 kg/d during the three weeks prior to d 0. T he ADG from d 22 to 14 (restriction through compensation) was nearly equal to the BW gains observed through the remainder of the trial ( d 14 d 42) for each treatment, indicating that the steers likely compensated for the lack of BW

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55 gain during the period of feed restriction A portion of the increase in BW gains during the first 14 d may be attributable to gut fill; however, these effec ts should have been minimized since steers had been consuming hay for 5 d prior to d 0 BW measurements. The steer performance results are in agreement with those reported by Stalker et al. (2007) in which growing heifers supplemented with DDG did not respo nd to additional dietary DIP when consuming a diet of ground corn cobs and sorghum silage. It is possible that the amount of N provided in the hay and basal SBH and DDG supplements was adequate to support rumen fermentation through N recycling. Therefore DIP was likely adequate, and steer performance would not have been influenced by additional dietary NPN. Forty two d estimated mea n daily hay DMI (Table 4 2 ) was calculated based on shrunk BW gain and net energy values of the feeds tuffs Based on the es timations, co product type, rather than addition of Optigen II affected voluntary hay DMI. No differences were observed between steers offered DDG and DDG+Opt treatments or steers offered SBH and SBH+Opt treatments ( P >0.10 ). Steers consuming DDG or DDG+ Opt had 62% greater ( P <0.05 ) estimated daily hay DMI compared to steers offered SBH or SBH+Opt. The differences in estimated mean hay DMI resulted in 18% greater ( P <0.05) total DMI for steers consuming the DDG supplements compared to steers receiving SBH (Table 4 2). The addition of Optigen had no effect ( P >0.10) on total DMI. The decreased DMI observed for steers consuming the SBH treatments may be a result of the greater amount of supplement offered compared to DDG treatments. Supplements were formulat ed to contain equal amounts of CP. Dried distillers grains have a greater c oncentration of CP compared to SBH, and as a result, steers in the SBH treatment were offered 1.4 kg/d more supplement compared to steers in the DDG treatment. However, the steers offered the DDG

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56 treatment consumed an estimated mean of 2.7 kg /d more hay; therefore, not all of the differences in hay intake between supplement types were the result of substi tution effects. In cattle with high energy requirements that are consuming low energy feeds, such as growing steers, BW gain is generally limited by the amount of feed the animal is able to consume (Allen, 1996). The SBH utilized in this experiment were 68% NDF whereas the DDG were 33% NDF. Greater concentrations of NDF in the die t are associated with decreased levels of intake (Van Soest, 1994). The NDF component of feedstuffs are retained within the rumen for longer periods of time compared to non fibrous feeds, resulting in an increased fill effect. The increased fill effect l eads to slower passage rates, and therefore, decreased amount of intake. While the level of NDF was greater in SBH than DDG, the lower hay DMI associated with steers consuming SBH resulted in no differences in NDF intake among treatments ( P =0.35, Table 4 2). Differences in hay DMI cannot be explained by total NDF intake; however, the particle size of the NDF rich SBH may have contributed to the decreased hay DMI compared to steers supplemented with DDG. The particle size of the pelleted SBH, while much s maller than that of the long stem hay, was not as small as the DDG. The DDG would have passed from the rumen to the omasum at a faster rate than the SBH, stimulating greater intake levels in steers consuming DDG compared to steers consuming SBH (Van Soest 1994). Galloway et al. (1993 ) determined that the passage rate of bermudagrass diets containing SBH supplements was about 4.5%/h. However, Martin and Hibberd (1990) noted that passage rate of low quality forage diets decreased from 3.81 %/h to 3.59 %/h as the level of SBH supplementation increased from 1 kg/d to 3 kg/d. Sniffen et al. (1992) indicated that the passage rate of high forage diets containing distillers grains may be as great as 4.0 %/h.

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57 Gain:feed was calculated using mean estimated daily h ay DMI and amount of supplement offered. Gain efficiency exhibited similar results as hay DMI. Co product type affected ( P <0.001) gain efficiency, while the addition of Optigen II did not ( P >0.10). There were no differences between DDG and DDG+Opt trea tments or SBH and SBH+Opt treatments ( P >0.10). Steers offered DDG and DDG+Opt had a mean gain efficiency of 0.10. However, steers offered SBH based supplements had mean gain efficiency of 0.13. Thus, steers consuming supplements containing SBH were appr oximately 25% more efficient at converting feed to BW compared to steers offered DDG based supplements. The differences in gain efficiency were mainly driven by the differences observed in hay DMI. Steers offered DDG treatments consumed greater amounts of hay. Steers offered DDG containing supplements, exhibited numerically lower BW gains compared to steers consuming the SBH and SBH+Opt treatments, resulting in greater gain efficiency for steers offered either of the SBH treatments. Physiological response As a result of the 5 d acclimation period prior to d 0, differences were observed in initial steer PUN concentrations (Table 4 3 ). Plasma urea nitrogen concentrations of steers consuming the SBH and SBH+Opt treatments w e re 45% less ( P <0.001) than steers consuming DDG and DDG+Opt treatments Optigen II was not included in the supplements until d 0; therefore, Optigen II did not affect initial PUN concent ration in steers consuming DDG or SBH ( P >0.10 ). On d 14, the steers consuming DDG and DDG+Opt contin ued to have greater ( P <0.001) PUN concentrations compared to steers consuming SBH and SBH+Opt. Additionally, the inclusion of Optigen II increased steer PUN concentrations by 31% ( P <0.05 ) when included in supplements containing DDG and by 84% in suppleme nts containing SBH ( P <0.05 ). Steer PUN concentrations were greatest in steers consuming DDG+Opt, and SBH supplemented steers had

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58 the lowest PUN concentrations. The addition of Optigen II to SBH increased steer PUN concentration so that SBH+Opt and DDG s upplemented steers were not different ( P >0.10 ). On d 28, the inclusion of Optigen II increased steer PUN concentratio ns by 28.2% in DDG supplements and by 38.0% in SBH supplements ( P <0.05 ) compared to steers not offered Optigen II. Steers consuming DDG +Opt maintained the greatest PUN concentrations, and steers offered only SBH had the lowest PUN concentrations. On d 28, Optigen II increased PUN concentrations when included in SBH supplements, but not to the concentrations observed in the only DDG trea tment as was seen on d 14 and 42. Plasma urea nitrogen concentrations of steers consuming SBH+Opt were 80% that of steers consuming DDG ( P <0.05 ). On d 42, steer PUN concentrations were greatest ( P <0.001) in steers offered DDG+Opt, followed by the steers on the DDG and SBH+Opt treatments which were not different ( P >0.10 ), followed by SBH supplemented steers. Supplements were formulated to contain equal concentrations of CP, and therefore, equal concentrations of N. However, the greater hay DMI observed in steers consuming DDG resulted in 40% greater ( P <0.001) N intake for DDG supplemented steers compared to SBH supplemented steers ( Table 4 2). Similarly, steers offered DDG+Opt consumed 35% greater ( P <0.001) amounts of N/d compared to steers offered SBH+ Opt. The greater level of N intake observed in steers offered DDG likely contributed to greater PUN concentrations compared to SBH. Additionally, the protein in SBH is degraded in the rumen to a greater extent than the protein found in DDG. Since the ba hiagrass hay was low in DIP, any protein from SBH degraded within the rumen was likely utilized by the microbes, with very little ammonia N being recycled out of the rumen to the liver. In contrast, most of the protein in DDG is not degraded in the rumen, and is instead degraded in the small intestine. The amino acids are then absorbed into

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59 the blood pool and travel to the liver. Here, some of the N from amino acids is converted to urea and reappears in the blood as urea N (Owens and Zinn, 1993). Plasma urea nitrogen concentrations above 12 mg/dL are associated with adequate dietary CP, and consequently, may indicate a potential for performance improvement through energy supplementation (Hammond et al., 1993) Therefore, steers offered the DDG+Opt treat ment may have exhibited improved performance with additional dietary energy. Additionally, Hammond et al. (1993) stated that cattle with PUN concentrations below 9 mg/dL are most likely to respond to protein supplementation when maintained on a tropical f orage based diet. The steers offered the SBH supplement were the only group of steers that consistently had PUN concentrations below 9 mg/dL, indicating that these steers may have benefited from additional protein supplementation. This is in contrast to results of Kostenbauder et al. (2007), in which SBH supplements increased PUN concentrations of steers consuming bahiagrass hay to levels above 9 mg/dL. The chemical composition of feedstuffs were similar to the feeds offered to steers in the current stud y; therefore, the conflicting results may have been the consequence of differences in hay and supplement intake. The increase in PUN concentration as a result of Optigen II supplementation was due to the increased concentration of N in the diet. Addition ally, Owens and Zinn (1993) have stated that the presence of urea increases the pH of the rumen fluid. This environment favors ammonia in the form of NH 3 rather than the ion form, NH 4 + The ammonia ion is not readily absorbed across the rumen wall, in c ontrast to NH 3 Therefore, ammonia from Optigen is likely absorbed across the rumen wall, and travels to the liver where it is converted to urea. Some of this urea may then reappear in the plasma as it is recycled to the rumen, salivary glands, or other body tissues (Owens and Zinn, 1993).

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60 The addition of urea to molasses supplements has been shown to increase PUN concentrations of steers and heifers consuming ad libitum bermudagrass hay (Stateler et al. 1995). Also, PUN concentrations in steers grazing bahiagrass pasture were greater when a molasses supplement contained 6.5% urea compared to molasses supplements containing 1.9% urea and various sources of natural protein (Pate et al. 1995). The supplement containing urea as the only source of CP also had the greatest level of degradable protein. The other supplements contained a small amount of urea and varying levels of feather meal and blood meal, balanced for CP. Feather meal and blood meal contain greater amounts of undegradable intake protein ( U IP ) in contrast to urea, which is 100% DIP. The greater level of DIP in the 6.5% urea supplement likely contributed to the greater PUN concentrations. Plasma glucose concentrations (Table 4 3 ) were not different ( P =0.33, 0.59, 0.98) among treatments on d 0, 28, and 42, respectively. Treatment affected ( P =0.04) plasma glucose concentrations on d 14. Steers supplemented with only SBH had the greatest plasma glucose concentrations (74.17 mg/dL). There were no differen ces between steers offered SBH and DD G or DDG+Opt diets ( P >0.10 ), but plasma glucose concentrations were greater ( P <0.05 ) for SBH supplemented steers than steers consuming SBH+Opt (62.30 mg/dL). Plasma glucose concentrations of steers on the SBH+Opt treatment were 84% that of steers consumin g only SBH and 85% that of steers consuming DDG+Opt ( P <0.05 ). Mean glucose concentration across all treatments at all collecti on dates was 69.0 mg/dL which i s consistent with the 68.8 mg/dL value reported by Alvarez et al. (2000). It has been shown that only about 10% of glucose utilized by ruminants originates from dietary sources absorbed across the gastrointestinal tract, as most glucose is produced by the animal through gluconeogenesis (Otchere et al., 1974; Young, 1977). However, glucose concentrati ons in cattle may be related to energy intake (Schmidt and Keith,

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61 1983). While there were differences ( P =0.06) in estimated total TDN intake (Table 4 2), only about 0.6 kg/d separated the group of steers that consumed the greatest amount of TDN compared t o those that consumed the least. These differences were likely not sufficient to elicit any changes in plasma glucose concentrations. As a result of the accli mation period prior to d 0, treatment differences ( P <0.001) were observed in initial daily urinary N excretion (Table 4 4 ). There were no differences between steers offered the DDG and DDG+Opt treatments or between steers offered the SBH and SBH+Opt treatments ( P >0.10 ). However, steers consuming DDG and DDG+Opt excreted 56.2 more g N/d ( P <0.05) compa red to steers consuming SBH and SBH+Opt on d 0. No treatment differences ( P =0.22) were observed on d 14. On d 28, supplement type had an effect ( P =0.003) on urinary N excretion. Steers supplemented with DDG+Opt (180.4 g/d) excreted 38% more ( P <0.05 ) uri nary N compared to steers supplemented with only DDG 53% more ( P <0.05 ) urinary N compared to steers supplemented with SBH+Opt, and 94% more ( P <0.05 ) g urinary N/d than steers consuming only SBH. Daily urinary N excretion of steers on the SBH+Opt treatmen t was not different from steers offered only SBH or only DDG ( P >0.10 ); however, steers on the DD G treatment excreted 38% more ( P <0.05 ) urinary N than steers on the SBH treatment No treatment differences ( P =0.54) were observed for urinary N excretion on d 42. Similar to PUN concentrations, urinary N excretion appears to have been related to calculated mean daily N intake. While not statistically significant ( P >0.10) urinary N excretion appeared to be greater for steers consuming DDG supplements compared to steers consuming SBH. The addition of Optigen II to the supplements of beef steers did not affect urinary N excretion, with the exception of DDG compared to DDG+Opt on d 28. This may suggest that despite the additional dietary N, Optigen II did not increase urinary N excretion, possibly

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62 resulting in greater N retention. Kohn et al. (2005) conducted a meta analysis in which they observed that cattle excreted a mean of 90 67 g N/d, which is similar to a majority of the values expressed by steers in this trial. Trial Two Steer performance At the initiation of the trial, steer BW (mean 274.5 26 kg, Table 4 5 ) did not differ ( P =0.99) among treatments. Between d 0 and 14, steers supplemented with D DG gained 55 % less ( P <0.05 ) than steers on all other t reatments. There were no differences in steer BW on d 14 ( P =0.96, mean = 282 kg) or on d 28 ( P =0.94, mean = 282 kg). Average daily gain from d 14 to 28 was not different ( P =0.55) among treatments. At the completion of the study on d 42, steer BW was not different ( P =0.79, mean = 306.1 kg). From d 28 to 42, ADG did not differ ( P =0.26) among treatments; however, there was a tendency ( P =0.10) for treatment to affect overall ADG from d 0 to 42. Steers consuming SBH alone gained 0.17 kg/d less than steers c onsuming SBH/DDG and 0.14 kg/d less than steers consuming DDG/SBH ( P <0.05 ). Supplement type affected ( P =0.01) mean estimated hay DMI ( Table 4 5 ); steers supplemented with only SBH consumed the greatest amount of hay across the 42 d experiment (3.85 kg/d), followed by steers offered the SBH/DDG and DDG treatments which were not different ( P >0.10). Steers in the DDG/SBH treatment consumed the least amount of hay (2.56 kg/d). Steers supplemented with only SBH consumed an average of 1.12 kg/d more estimated hay DM than steers offered only DDG ( P <0.05 ), and 1.29 kg/d more estimated hay DM than steers offered DDG/SBH ( P <0.05 ). Steers supplemented with SBH/DDG consumed an average of 0.92 more kg/d compared to steers supplemented with DDG/SBH ( P <0.05 ). Differe nces were also observed ( P <0.05) in estimated total DMI (Table 4 5), with steers offered only or mostly SBH consuming 24% more DM compared to steers offered only or mostly DDG.

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63 The amount of NDF consumed increased with the amount of SBH offered in the supp lement ( P <0.001). Greater levels of dietary NDF are typically associated with decreased forage DMI (Van Soest, 1994). The steers offered the SBH treatment, while consuming the greatest amount of NDF, also consumed the greatest amount of hay /d. Therefor e, the differences in hay intake were likely not a result of diet NDF concentration, but instead may have been affected by gut fill (Allen, 1996). It is possible that the steers consuming only SBH attempted to consume enough hay to meet their energy and p rotein requirements for growth. Concentrations of PUN indicate that the steers required additional dietary protein (Hammond et al., 1993), while the TDN:CP of the hay was 6.6, which may indicate that forage protein and energy are balanced (Moore et al., 1 999). Based on the principles outlined by Hammond et al. (1993), steers consuming a combination of DDG and SBH were not deficient in energy relative to protein. The decreased voluntary hay intake in these steers may signify that they did not consume amou Gain:feed was calculated utilizing mean estimated daily hay DMI and the amount of supplement offered, with treatment affecting ( P <0.001) gain efficiency. Steers consuming DDG/SBH were most efficient ( P <0.05), followed by the DDG and SBH/DDG treatments, which were not different ( P >0.10). Steers supplemented with SBH only were least efficient, with a gain efficiency of 0.03 less than steers supplemented with DDG and SBH/DDG, and 0.05 less th an steers supplemented with DDG/SBH ( P <0.05). Steers consuming DDG or SBH/DDG averaged 0.018 fewer ( P <0.05) kg of gain per kg of feed compared to steers consuming DDG/SBH. Physiological response Prior to the initiation of the experiment, steers were suppl emented with approximately 2.7 kg/d of SBH for five d. As a result, no treatment differences ( P =0.68) were observed in PUN

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64 concentrations on d 0 (Table 4 6 ). However, on d 14, PUN concentration increased ( P <0.01) as the amount of DDG offered in the suppl ement increased. Steers supplemented with only SBH had a mean PUN concentration of 5.31 mg/dL. Substituting a small amount of energy from SBH with DDG resulted in an 85% increase ( P <0.05 ) in PUN concentrations of steers on the SBH/DDG treatment whereas, steers supplemented with the DDG/SBH treatment had 24% greater ( P < 0.05) PUN concentrations compared to steers offered SBH/DDG. Steers supplemented with DDG had the greatest ( P <0.05) PUN concentrations, with 36.9% greater concentrations compared to DDG/SB H supplemented steers. Similar patterns were observed on d 28; PUN concentrations increased ( P <0.001) with the amount of DDG in the diet. Steers consuming SBH only had the lowest mean PUN concentration, with 5.64 mg/dL. Steers supplemented with SBH/DDG had 49% greater ( P <0.05 ) PUN concentration than steers offered only SBH. Steers consuming DDG/SBH had 37% greater ( P <0.05 ) PUN concentration compared to steers offered SBH/DDG, wherea s steers supplemented with only DDG had 21% greater ( P <0.05 ) PUN concent ration compared to steers offered DDG/SBH. Treatment differences were observed ( P <0.001) on d 42. Steers consuming DDG only had the greatest PUN concentrations; however, differences were not observed ( P >0.10 ) between steers consuming the DDG and DDG/SBH treatments Additionally, there were no differences ( P >0.10 ) between steers on the DDG/SBH and SBH/DDG treatments ; however, steers supplemented with only DDG had greater ( P <0.05 ) PUN concentration than steers offered the SBH/DDG supplement Steers supple mented with SBH had PUN concentration that were 57% less than steers offered SBH/DDG 49% that of steers offered DDG/SBH ( P <0.05 ), and 47% that of steers offered only DDG ( P <0.001).

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65 The effects of treatment on steer PUN were directly related to the amou nt of supplemental protein offered. Total dietary N intake was greatest ( P <0.001; Table 4 5) for steers on the only DDG diet, and decreased with the amount of DDG offered, with steers offered only SBH consuming the least amount of N/d. The greater supply of dietary N resulted in greater amounts of stored N, which appeared in the blood as PUN. Supplementation of natural protein has been shown to increase PUN concentrations in ruminants consuming low quality forages (Bohnert et al., 2002b; Poore et al., 20 06). As previously stated, Hammond et al. (1993) suggested that PUN concentrations above 12 indicate adequate dietary CP, and cattle may benefit from energy supplementation in this situation. Furthermore, PUN concentrations below 9 indicate that dietary protein is inadequate, and protein supplements may enhance cattle performance. The steers offered only DDG consistently had PUN concentrations in excess of 12 mg/dL, and therefore, additional dietary energy may have improved performance. Additionally, st eers offered only SBH never achieved PUN concentrations above 7 mg/dL, which indicates that protein was not sufficient to maximize steer performance. The steers that received a combination of co products had PUN concentrations that ranged from 8.4 mg/dL t o 12.1 mg/dL throughout the experiment after d 0. These results further illustrate the metabolic advantage of supplemental protein and energy, which tended to improve overall ADG above the SBH supplement, and increased gain efficiency in steers offered th e DDG/SBH treatment. There were no treatment differences ( P 28, and 42. Plasma glucose concentrations have been shown to be related to energy intake (Schmidt and Keith, 1983); however, differences in tota l TDN intake by steers in this trial (Table 4 5) did not affect plasma glucose. Intake of TDN followed a similar pattern to total DMI, with steers offered only or mostly SBH consuming the greatest amount of TDN ( P <0.05), while steers

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66 on the DDG and DDG/SB H treatments consumed the least amount. While statistically significant, intake ranged from 5.81 to 7.43 kg TDN/d. It is possible that the range of 1.62 kg TDN/d was likely not sufficient to result in discernable differences in plasma glucose concentrati ons, particularly since only about 10% of total plasma glucose originates from dietary sources (Otchere et al., 1974; Young, 1977). Economic analysis A simple economic analysis was conducted to determine the most desirable supplement combination for produc ers (Table 4 7). The prices paid for the feedstuffs were as follows: Hay, $30/bale; DDG, $182/T; SBH, $155/T. Based on the prices paid for the supplements, the cost/kg of each supplement were as follows: DDG, $0.20; DDG/SBH, $0.19; SBH/DDG, $0.18; SBH, $ 0.17. Accounting for cost of hay and supplement consumed, the DDG and DDG/SBH diets were least expensive at $36.11 and $37.41, respectively, and were not different ( P >0.10). The SBH/DDG and SBH supplement costs were $39.39 and $40.12, respectively, and w ere not different ( P> 0.10) from DDG, but were more expensive ( P <0.05) than DDG/SBH. The cost of BW gain was determined based on the cost of total feed. Steers consuming the SBH treatment had the greatest ( P <0.05) cost of BW gain at $1.50/kg, compared to the other three treatments which ranged from $1.10/kg to $1.30/kg. The SBH were the least economically efficient as a result of their low BW gains and high hay intakes. These results may indicate that the combinations of co products were more cost effici ent compared to DDG or SBH alone. The price of each co product should determine the most economically desirable proportions of DDG and SBH used to background steers. Implications In Trial One, additional DIP did not affect steer performance. T he SBH trea tment was the most effective, as these steers exhibited the greatest feed efficiency. While Optigen II addition

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67 increased PUN concentrations to more desirable levels in DDG and SBH diets, it did not affect performance. The cost associated with feeding t his additional source of DIP would not make this diet an economical alternative. In Trial Two, the combination of mostly DDG was the most efficient and economical supplement. The other two supplements containing DDG also outperformed the SBH only diet. Therefore, the SBH treatment alone is not a desirable supplement to growing steers when fed at this level or in combination with this hay. Growing steers require more protein than they are able to consume from a diet of bahiagrass hay with SBH supplementa tion. The cost of the co product supplements should dictate the most desirable combinations to feed to growing beef steers.

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68 Table 4 1. Composition of feedstuffs fed to growing beef steers. Bahiagrass hay Dried distillers grains Soybean hulls Experime nt One DM, % 92.0 87.1 89.3 % of DM OM 93.7 94.1 96.1 CP 8.5 32.3 12.5 DIP, % CP 52.2 27.3 58.0 a NDF 70.3 32.5 67.6 ADF 38.7 16.7 47.6 TDN 62.1 65.7 70.6 Experiment Two DM, % 92.3 88.1 89.1 % of DM OM 93.4 93.8 96.1 CP 9.7 31.0 12.7 DIP, % CP 50.2 28.5 58.0 a NDF 69.0 33.8 65.7 ADF 39.0 15.5 48.3 TDN 64.5 65.7 72.0 a NRC (2000) tabular value.

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69 Table 4 2. Effect of co product source and Optigen II supplementatio n on steer bodyweight (BW), BW gain and intake (Trial One). Treatment a Item DDG DDG+Optigen SBH SBH+Optigen SEM b P value BW, kg d 0 237 237 238 234 7.1 0.97 d 14 255 256 257 256 7.5 1.00 d 28 262 262 266 257 7.4 0.86 d 42 273 273 276 271 7.4 0.97 BW gain, kg/d d 0 14 1.27 1.35 1.32 1.45 0.10 0.63 d 14 28 0.45 0.46 0.70 0.61 0.14 0.47 d 28 42 0.79 0.76 0.66 0.82 0.10 0.74 d 0 42 0.84 0.86 0.90 0.95 0.04 0.17 Mean hay DMI, kg/d 7.02 d 7.20 d 4.33 e 4.44 e 0.29 <0.001 Total DMI, kg/d 8.20 d 8.43 d 6.97 e 7.12 e 0.29 <0.001 N Intake, g/d c 165.65 d 188.05 e 118.02 f 139.37 g 3.93 <0.001 TDN Intake, kg/d c 5.24 de 5.37 d 4.78 f 4.84 ef 0.18 0.06 NDF Intake, kg/d c 5.38 5.50 5.04 5.12 0.20 0.35 Gain:Feed, kg:kg 0.10 d 0.10 d 0.12 e 0.13 e 0.005 <0.001 a Least square means; Treatment: DDG, dried distillers grains; DDG+Optigen, dried distillers grains plus Optigen II, SBH, soybean hulls; SBH+Opt, soybean hulls plus Optigen II. b Standard error of the mean, n =56. c Estimated total dietary intake (hay and supplement). d, e, f g Means with different superscripts within a row are different ( P <0.05).

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70 Table 4 3. Effect of co product source and Optigen II supplementation on steer plasma glucose and urea nitrog en concentration (Trial One). Treatment a Item DDG DDG+Opt SBH SBH+Opt SEM b P value PUN c mg/dL d 0 10.17 d 11.49 d 4.06 e 5.67 e 0.72 <0.001 d 14 10.70 d 14.02 e 5.51 f 10.12 d 0.82 <0.001 d 28 10.69 d 13.70 e 6.17 f 8.51 g 0.67 <0.001 d 42 10.35 d 13.43 e 7.87 f 10.30 d 0.66 <0.001 Glucose, mg/dL d 0 63.90 67.52 69.21 71.96 3.10 0.33 d 14 69.17 de 73.35 d 74.17 d 62.30 e 3.17 0.04 d 28 64.79 72.04 67.98 67.36 3.81 0.59 d 42 70.94 70.32 69.69 69.72 2.56 0.98 a Least square mean s; Treatment: DDG, dried distillers grains; DDG+Optigen, dried distillers grains plus Optigen II, SBH, soybean hulls; SBH+Opt, soybean hulls plus Optigen II. b Standard error of the mean, n=56. c Plasma urea nitrogen. d, e, f, g Means with different supe rscripts within a row are different ( P <0.05). Table 4 4. Effect of co product source and Optigen II supplementation on daily urinary nitrogen excretion (Trial One). Treatment a DDG DDG+Opt SBH SBH+Opt SEM b P value Urinary N, g/d d 0 102.11 c 125.41 c 53.40 d 61.64 d 10.37 <0.001 d 14 162.11 144.62 77.74 110.33 33.70 0.22 d 28 130.67 c 180.40 d 92.93 e 118.32 ce 15.20 0.003 d 42 113.01 110.05 112.77 141.78 22.32 0.54 a Least square means; Treatment: DDG, dried distillers grains; DDG+Optige n, dried distillers grains plus Optigen II, SBH, soybean hulls; SBH+Opt, soybean hulls plus Optigen II. b Standard error of the mean, n=19, 23, 27, 22 for d 0, 14, 28, 42, respectively. c, d, e Means with different superscripts within a row are different ( P <0.05).

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71 Table 4 5. Effect of dried distillers grains (DDG) and/or soybean hulls (SBH) supplementation on steer bodyweight (BW), BW gain and intake (Trial Two). Treatment a Item DDG DDG/SBH SBH/DDG SBH SEM b P value BW, kg d 0 274.3 276.1 274.9 272.6 7.26 0.99 d 14 278.8 283.6 283.6 281.4 7.54 0.96 d 28 291.4 296.8 294.9 290.8 7.82 0.94 d 42 304.4 309.9 309.8 300.3 7.82 0.79 BW gain, kg/d d 0 14 0.33 d 0.54 de 0.62 e 0.63 e 0.08 0.03 d 14 28 0.90 0.94 0.81 0.6 7 0.14 0.55 d 28 42 0.93 0.94 1.07 0.68 0.14 0.26 d 0 42 0.72 de 0.80 d 0.83 d 0.66 e 0.05 0.10 Mean hay DMI, kg/d 2.73 de 2.56 d 3.48 ef 3.85 f 0.29 0.01 Total DMI, kg/d 5.20 d 5.14 d 6.16 e 6.63 e 0.29 0.001 N Intake, g/d c 180.45 d 154.67 e 142.40 f 122.15 g 4.48 <0.001 TDN Intake, kg/d c 5.81 d 5.98 d 6.91 e 7.43 f 0.19 <0.001 NDF Intake, kg/d c 3.96 d 4.63 e 6.10 f 7.16 g 0.20 <0.001 Gain:Feed 0.12 d 0.14 e 0.12 d 0.09 f 0.01 <0.001 a Least square means; Treatment: DDG, 2.8 kg dried distillers grains ; DDG/SBH, 1.9 kg DDG, 0.98 kg soybean hulls; SBH/DDG, 0.96 kg DDG, 2.05 kg SBH; SBH, 3.12 kg SBH. b Standard error of the mean, n=56. c Estimated total dietary intake (hay and supplement). d, e, f g Means with different superscripts within a row are diff erent ( P <0.05 ).

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72 Table 4 6. Effect of dried distillers grains (DDG) and/or soybean hulls (SBH) supplementation on steer plasma glucose and urea nitrogen concentration. Treatment a Item DDG DDG/SBH SBH/DDG SBH SEM b P value PUN c mg/dL d 0 6.7 5 6.17 6.13 6.44 0.41 0.68 d 14 16.57 d 12.10 e 9.80 f 5.31 g 0.81 <0.001 d 28 14.01 d 11.55 e 8.42 f 5.64 g 0.70 <0.001 d 42 12.53 d 11.86 de 10.24 e 5.86 f 0.83 <0.001 Glucose, mg/dL d 0 77.24 74.49 75.19 74.51 3.69 0.94 d 14 78.88 76.3 0 79.56 76.64 3.92 0.90 d 28 80.38 75.69 76.25 76.29 4.06 0.83 d 42 80.76 75.82 76.79 75.66 4.29 0.78 a Least square means; Treatment: DDG, 2.8 kg dried distillers grains; DDG/SBH, 1.9 kg DDG, 0.98 kg soybean hulls; SBH/DDG, 0.96 kg DDG, 2.05 kg SBH ; SBH, 3.12 kg SBH. b Standard error of the mean, n=56. c Plasma urea nitrogen. d, e, f g Means with different superscripts within a row are different ( P <0.05 ). Table 4 7. Economics of supplementing dried distillers grains (DDG) or soybean hulls (SBH). Treatment a Item DDG DDG/SBH SBH/DDG SBH SEM b P value Supplement cost, $/kg c 0.20 0.19 0.18 0.17 ----Feed cost, $/steer/d d 0.89 ef 0.86 e 0.94 f 0.96 f 0.03 0.07 Total feed, $/steer 37.41 ef 36.11 e 39.39 f 40.12 f 1.15 0.07 Cost of gain, $/kg BW g ain/steer 1.30 e 1.10 f 1.22 ef 1.50 g 0.07 0.003 a Least square means; Treatment: DDG, 2.8 kg dried distillers grains; DDG/SBH, 1.9 kg DDG, 0.98 kg soybean hulls; SBH/DDG, 0.96 kg DDG, 2.05 kg SBH; SBH, 3.12 kg SBH. b Standard error of the mean, n=56. c Cost of supplements: $182/T DDG, $155/T SBH. d Cost of hay and supplement consumed per steer/d; hay cost, $30/bale. e f, g Means with different superscripts within a row are different ( P <0.05).

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83 BIOGRAPHICAL SKETCH Jacqueline Wahrmund was born in Baton Rouge, Louisiana, and grew up in Louisville, Kentucky. She began riding horses at a young age, and after graduating from high school, her love of horses prompted her to enter the animal science pro gram at the University of Kentucky. While attending UK, she began work in the ruminant nutrition laboratory and at the UK Beef Unit where she assisted with beef cattle nutrition research. She was a member of Delta Zeta Sorority, and the Daughters of the American Revolution. After graduating from UK with BS degrees in animal science and agricultural economics, nutrition. Upon graduation from UF, she plans to attend Oklahoma State University, where she will continue to study beef nutrition in pursuit of her PhD. She remains involved in the horse industry as a breeder of American Saddlebred show horses.