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Effects of Forage Sampling Method on Nutritive Value of Bahiagrass

Permanent Link: http://ufdc.ufl.edu/UFE0022825/00001

Material Information

Title: Effects of Forage Sampling Method on Nutritive Value of Bahiagrass
Physical Description: 1 online resource (119 p.)
Language: english
Creator: Hughes, Ashley
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: availability, bahiagrass, cattle, forage, method, notatum, nutritive, paspalum, sampling, selection, value
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: As with many tropical grasses, the nutritive value of bahiagrass (Paspalum notatum) has been reported to be relatively low. However, the data that does exist is based on hand-harvested samples and does not account for the ability of cattle to selectively graze within a pasture. Previous research has shown that the hand-sampled forage is inaccurate in its estimation of a grazing animal?s selected diet. The objective of this study was to characterize the nutritive value of forage selected by grazing cattle compared to hand-collected forage during the winter and spring (December to May), as well as the summer and fall seasons (June to November). Four locations were utilized to represent variation in the Florida pasture landscape, the locations included: Range Cattle Research and Education Center, Ona; USDA- Subtropical Agricultural Research Station, Brooksville; Santa Fe River Ranch Beef Unit, Alachua; and North Florida Research and Education Center, Marianna. Forage availabilities (FA) were visually assigned to selected pastures, as either HIGH or LOW, to represent differences in forage quantity between pastures at each location. Forage and masticate samples were collected from each of the four locations from December 2006 to November 2007. Samples were analyzed to determine forage mass, in vitro digestible organic matter (IVDOM), crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF) concentrations. Selection indices (SI) were also determined for each chemical analysis. Hand shears were used to cut the forage to an approximate height of 3.5 cm within a 0.25-m quadrat; masticate samples were collected using eight ruminally fistulated steers (two steers/location). During the winter and spring, masticate samples consistently had greater (P < 0.001) IVDOM concentration (mean=59.1%) and CP concentration (mean=12.3%) compared to hand-collected forage samples (45.8% IVDOM; 10.5% CP). Concentration of IVDOM and CP of masticate and forage samples was also affected by month (P < 0.001) resulting in a type x month effect for IVDOM and CP concentration (P < 0.001 and P=0.02, respectively). Selection indices of IVDOM differed between FA (P=0.04) and month (P < 0.001). The SI for IVDOM within the LOW FA was 10% greater compared to the HIGH FA. The selection index for CP concentration was also affected by FA (P=0.01) and month (P=0.03). The SI for CP within the LOW FA was nearly 20% greater than that for the HIGH FA. This indicates the steers were more selective of forage material within the LOW FA compared to the HIGH FA for IVDOM and CP concentration during the winter and spring. During the summer and fall, masticate samples consistently had greater (P < 0.001) IVDOM concentration (mean=60.8%) and CP concentration (mean=11.2%) compared to hand-collected forage samples (51.7% IVDOM; 9.6% CP). Concentration of IVDOM and CP of masticate and forage samples was also affected by month (P < 0.001) resulting in a type x month effect for IVDOM and CP concentration (P=0.08 and P < 0.001, respectively). Selection indices for IVDOM did not differ between FA (P=0.48) or month (P=0.43). However, the steers selected forage material that was nearly 19% greater in IVDOM concentration compared to hand-collected forage samples. The selection index for CP concentration was also not affected by FA (P=0.72) or month (P=0.16). However, the steers selected forage material that was 20% greater in CP concentration compared to hand-collected forage samples during the summer and fall. Throughout the year, steers will selectively graze bahiagrass forage that is greater in IVDOM and CP concentration compared to forage collected by hand-sampling, thus influencing supplementation recommendations for cow-calf producers.
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 Ashley Hughes.
Thesis: Thesis (M.S.)--University of Florida, 2008.
Local: Adviser: Hersom, Matthew J.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2009-12-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0022825:00001

Permanent Link: http://ufdc.ufl.edu/UFE0022825/00001

Material Information

Title: Effects of Forage Sampling Method on Nutritive Value of Bahiagrass
Physical Description: 1 online resource (119 p.)
Language: english
Creator: Hughes, Ashley
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2008

Subjects

Subjects / Keywords: availability, bahiagrass, cattle, forage, method, notatum, nutritive, paspalum, sampling, selection, value
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: As with many tropical grasses, the nutritive value of bahiagrass (Paspalum notatum) has been reported to be relatively low. However, the data that does exist is based on hand-harvested samples and does not account for the ability of cattle to selectively graze within a pasture. Previous research has shown that the hand-sampled forage is inaccurate in its estimation of a grazing animal?s selected diet. The objective of this study was to characterize the nutritive value of forage selected by grazing cattle compared to hand-collected forage during the winter and spring (December to May), as well as the summer and fall seasons (June to November). Four locations were utilized to represent variation in the Florida pasture landscape, the locations included: Range Cattle Research and Education Center, Ona; USDA- Subtropical Agricultural Research Station, Brooksville; Santa Fe River Ranch Beef Unit, Alachua; and North Florida Research and Education Center, Marianna. Forage availabilities (FA) were visually assigned to selected pastures, as either HIGH or LOW, to represent differences in forage quantity between pastures at each location. Forage and masticate samples were collected from each of the four locations from December 2006 to November 2007. Samples were analyzed to determine forage mass, in vitro digestible organic matter (IVDOM), crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF) concentrations. Selection indices (SI) were also determined for each chemical analysis. Hand shears were used to cut the forage to an approximate height of 3.5 cm within a 0.25-m quadrat; masticate samples were collected using eight ruminally fistulated steers (two steers/location). During the winter and spring, masticate samples consistently had greater (P < 0.001) IVDOM concentration (mean=59.1%) and CP concentration (mean=12.3%) compared to hand-collected forage samples (45.8% IVDOM; 10.5% CP). Concentration of IVDOM and CP of masticate and forage samples was also affected by month (P < 0.001) resulting in a type x month effect for IVDOM and CP concentration (P < 0.001 and P=0.02, respectively). Selection indices of IVDOM differed between FA (P=0.04) and month (P < 0.001). The SI for IVDOM within the LOW FA was 10% greater compared to the HIGH FA. The selection index for CP concentration was also affected by FA (P=0.01) and month (P=0.03). The SI for CP within the LOW FA was nearly 20% greater than that for the HIGH FA. This indicates the steers were more selective of forage material within the LOW FA compared to the HIGH FA for IVDOM and CP concentration during the winter and spring. During the summer and fall, masticate samples consistently had greater (P < 0.001) IVDOM concentration (mean=60.8%) and CP concentration (mean=11.2%) compared to hand-collected forage samples (51.7% IVDOM; 9.6% CP). Concentration of IVDOM and CP of masticate and forage samples was also affected by month (P < 0.001) resulting in a type x month effect for IVDOM and CP concentration (P=0.08 and P < 0.001, respectively). Selection indices for IVDOM did not differ between FA (P=0.48) or month (P=0.43). However, the steers selected forage material that was nearly 19% greater in IVDOM concentration compared to hand-collected forage samples. The selection index for CP concentration was also not affected by FA (P=0.72) or month (P=0.16). However, the steers selected forage material that was 20% greater in CP concentration compared to hand-collected forage samples during the summer and fall. Throughout the year, steers will selectively graze bahiagrass forage that is greater in IVDOM and CP concentration compared to forage collected by hand-sampling, thus influencing supplementation recommendations for cow-calf producers.
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 Ashley Hughes.
Thesis: Thesis (M.S.)--University of Florida, 2008.
Local: Adviser: Hersom, Matthew J.
Electronic Access: RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2009-12-31

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2008
System ID: UFE0022825:00001


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1 EFFECTS OF FORAGE SAMPLING METHOD ON NUTRITIVE VALUE OF BAHIAGRASS By ASHLEY LYNN HUGHES A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2008

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2 2008 Ashley Lynn Hughes

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3 To Hank and McLovin. Thank you for your continued support and dedicati on during this project. Your steadfast work ethics and incredible personalities through all of th e challenges we have faced helped to enable the success of this research.

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4 ACKNOWLEDGMENTS I would like to thank, first and forem ost, Dr. Matt Hersom for his in credible guidance and understanding as the chair of my supervisory committee. Despite encountering numerous unforeseen obstacles during this program, Dr. Hersom has enabled and encouraged my success through all odds. I would also like to extend my gratitude to Dr. Ad egbola Adesogan and Dr. Joao Vendramini for their service and contributio n as members of my graduate committee. I would like to thank Dr. Mary Be th Hall and Dr. Adesogan for givi ng me the opportunity to learn and grow in the ruminant nutriti on lab and gain an unexpected love of the nutrition world. The graduate students under whom I worked should also be recognized for their guidance and motivation from one degree to the next: Jamie Fo ster, Nathan Krueger, Kathy Arriola, Bruno do Amaral, Lucia Holtshausen, Celeste Kearney, Dervin Dean, Faith Cullens, and Colleen Casey. I will always remember these individuals who have s hown me that education is a gift that you give to yourself which no one can take from you. Dr. Todd Thrift also deserves my appreciation for his advice and constant scrutiny which has inspir ed my personal and professional endeavors. I would like extend deep and meaningful thanks to all who have helped during this project. I would like to thank the farm crews at the Range Cattle Research and Education Center, USDASubtropical Agricultural Resear ch Station, Santa Fe River Ranc h Beef Unit (Boston Farm), and North Florida Research and Edu cation Center. I would like speci fically thank Austin Bateman, Eugene Rucks, Jamie Bradley, Todd Matthews, a nd David Thomas for their amazing support and patience through all of the obstacles this trial has presented. Also, I will never be able to truly express the level of gratitude I have for all of the unfortunate souls who have had to accompany me on the monthly adventures across the state of Florida for the sake of research; I would to thank Dr. Hersom, Jackie Wahrmund, Dusty Holley, Scot Eubanks, Reyna Speckmann, Lauren Dillard, Eduardo Alava, Julie Driscoll, and Mega n Thomas. In addition, I would like to thank

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5 my steers for constantly challenging my abilitie s as a cow whisperer and for furthering my knowledge of the peculiaritie s that cattle can possess. I would also like to thank my amazing friends, Julie Driscoll, Adriane Bell, Lauren Dillard, Nicky Brashear, Katie Roberts, Ginger Lars on, Megan Thomas, Jackie Wahrmund, Katie Webb, J.G. Vickers, and Scott Johnson for their neverending support and kindness. I would like to express my utmost appreciation to these incredible people for helping me to cope with the trials of this project: from crazy steers to hospital visits to immeasurable advice; I, as well as my sanity, thank you from the bottom of my heart. Last, however certainly not leas t, I would like to thank my parents, Vince and Jennifer Rossignol, and grandparents, Cal and Sylvia Waldr on, for their love and support. I would never have been able to accomplish this de gree and my goals in life without you.

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6 TABLE OF CONTENTS page ACKNOWLEDGMENTS ............................................................................................................... 4LIST OF TABLES ...........................................................................................................................8LIST OF FIGURES .......................................................................................................................11ABSTRACT ...................................................................................................................... .............12CHAPTER 1 INTRODUCTION .................................................................................................................. 152 LITERATURE REVIEW .......................................................................................................16Predominant Florida Forages .................................................................................................. 16Bahiagrass .................................................................................................................... ....17Bermudagrass .................................................................................................................. 20Limpograss .................................................................................................................... ..22Comparison of Florida Forages ....................................................................................... 24Beef Cattle Nutritional Requirements .................................................................................... 26Factors Affecting Requirements ......................................................................................27Plant-Animal Interface ........................................................................................................ ....343 EFFECTS OF FORAGE SAMPLING M ETHOD ON NUTRITIVE VALUE OF BAHIAGRASS DURI NG THE WINTER AND SPRING .................................................... 41Introduction .................................................................................................................. ...........41Materials and Methods ...........................................................................................................42Locations and Collections ............................................................................................... 42Laboratory Analysis ........................................................................................................ 44Statistical Analysis .......................................................................................................... 44Results and Discussion ........................................................................................................ ...45Forage Mass .....................................................................................................................45In Vitro Digestible Organic Matter .................................................................................46Crude Protein ...................................................................................................................49Neutral Detergent Fiber ...................................................................................................52Acid Detergent Fiber .......................................................................................................53Implications .................................................................................................................. ..........55

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7 4 EFFECTS OF FORAGE SAMPLING M ETHOD ON NUTRITIVE VALUE OF BAHIAGRASS DURI NG THE SUMMER AND FALL ...................................................... 60Introduction .................................................................................................................. ...........60Materials and Methods ...........................................................................................................61Locations and Collections ............................................................................................... 61Laboratory Analysis ........................................................................................................ 63Statistical Analysis .......................................................................................................... 63Results and Discussion ........................................................................................................ ...64Forage Mass .....................................................................................................................64In Vitro Digestible Organic Matter .................................................................................65Crude Protein ...................................................................................................................68Neutral Detergent Fiber ...................................................................................................70Acid Detergent Fiber .......................................................................................................73Implications .................................................................................................................. ..........745 SUMMARY, CONCLUSIONS, AND RECOMMENDATIONS .........................................80APPENDIX A WINTER / SPRING ...............................................................................................................83B SUMMER / FALL ..................................................................................................................96LITERATURE CITED ................................................................................................................109BIOGRAPHICAL SKETCH .......................................................................................................119

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8 LIST OF TABLES Table page 3-1 Effect of forage availability and m onth on overall m ean forage mass (kg/ha). ................. 563-2 Effect of sampling type and month on chemical composition of bahiagrass. ................... 563-3 Effect of forage availability on chemical analysis of bahiagrass. ...................................... 573-4 Effect of forage availability and month on steer selection indexa of bahiagrass forage. ... 583-5 Precipitation data (cm) Winter 2006 and spring 2007. .................................................... 593-6 Temperature data (0C) Winter 2006 and spring 2007. ..................................................... 594-1 Effect of forage availability and m onth on overall mean forage mass (kg/ha). ................. 764-2 Effect of sampling type and month on chemical composition of bahiagrass. ................... 764-3 Effect of forage availability on chemical analysis of bahiagrass. ...................................... 774-4 Effect of forage availability and month on steer selection index of bahiagrass forage. .... 784-5 Precipitation data (cm) Summer and fall 2007. ............................................................... 794-6 Temperature data (0C) Summer and fall 2007. ................................................................ 79A-1 Effect of forage availability and month on overall mean forage mass (kg/ha) at Ona. ..... 84A-2 Effect of sampling type and month on ch emical composition of bahiagrass at Ona. ........ 84A-3 Effect of forage availability on chem ical analysis of bahiagrass at Ona. .......................... 85A-4 Effect of forage availability and month on steer selection index of bahiagrass forage at Ona. ................................................................................................................................86A-5 Effect of forage availability and m onth on overall mean forage mass (kg/ha) at Brooksville. .................................................................................................................. ......86A-6 Effect of sampling type and month on chemical composition of bahiagrass at Brooksville. .................................................................................................................. ......87A-7 Effect of forage availability on chemical analysis of bahiagra ss at Brooksville. .............. 88A-8 Effect of forage availability and month on steer selection index of bahiagrass forage at Brooksville. ....................................................................................................................89

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9 A-9 Effect of forage availability and month on overall m ean forage mass (kg/ha) at Santa Fe........................................................................................................................................89A-10 Effect of sampling type and month on ch emical composition of bahiagrass at Santa Fe........................................................................................................................................90A-11 Effect of forage availability on chemi cal analysis of bahiagrass at Santa Fe. ................... 91A-12 Effect of forage availability and month on steer selection index of bahiagrass forage at Santa Fe. .........................................................................................................................92A-13 Effect of forage availability and m onth on overall mean forage mass (kg/ha) at Marianna. ..................................................................................................................... ......92A-14 Effect of sampling type and month on chemical composition of bahiagrass at Marianna. ..................................................................................................................... ......93A-15 Effect of forage availability on chemi cal analysis of bahiag rass at Marianna. .................94A-16 Effect of forage availability and month on steer selection index of bahiagrass forage at Marianna. .......................................................................................................................95B-1 Effect of forage availability and month on overall mean forage mass (kg/ha) at Ona. ..... 97B-2 Effect of sampling type and month on ch emical composition of bahiagrass at Ona. ........ 97B-3 Effect of forage availability on chem ical analysis of bahiagrass at Ona. .......................... 98B-4 Effect of forage availability and month on steer selection index of bahiagrass forage at Ona. ................................................................................................................................99B-5 Effect of forage availability and m onth on overall mean forage mass (kg/ha) at Brooksville. .................................................................................................................. ......99B-6 Effect of sampling type and month on chemical composition of bahiagrass at Brooksville. .................................................................................................................. ....100B-7 Effect of forage availability on chemical analysis of bahiagra ss at Brooksville. ............ 101B-8 Effect of forage availability and month on steer selection index of bahiagrass forage at Brooksville. ..................................................................................................................102B-9 Effect of forage availability and month on overall mean forage mass (kg/ha) at Santa Fe......................................................................................................................................102B-10 Effect of sampling type and month on ch emical composition of bahiagrass at Santa Fe......................................................................................................................................103B-11 Effect of forage availability on chemi cal analysis of bahiagrass at Santa Fe. ................. 104

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10 B-12 Effect of forage availability and month on steer selection index of bahiagrass forage at Santa Fe. .......................................................................................................................105B-13 Effect of forage availability and m onth on overall mean forage mass (kg/ha) at Marianna. ..................................................................................................................... ....105B-14 Effect of sampling type and month on chemical composition of bahiagrass at Marianna. ..................................................................................................................... ....106B-15 Effect of forage availability on chemi cal analysis of bahiag rass at Marianna. ...............107B-16 Effect of forage availability and month on steer selection index of bahiagrass forage at Marianna. .....................................................................................................................108

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11 LIST OF FIGURES Figure page 5-1 Nutrient requirement cycles and pasture characteristics ....................................................82

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12 Abstract of Dissertation Pres ented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science EFFECTS OF FORAGE SAMPLING METHOD ON NUTRITIVE VALUE OF BAHIAGRASS By Ashley Lynn Hughes December 2008 Chair: Matt Hersom Major: Animal Sciences As with many tropical grasses, th e nutritive value of bahiagrass (Paspalum notatum) has been reported to be relatively low. However, the data that does exist is based on hand-harvested samples and does not account for the ability of ca ttle to selectively graze within a pasture. Previous research has shown that the hand-sample d forage is inaccurate in its estimation of a grazing animals selected diet. The objective of this study was to characterize the nutritive value of forage selected by grazing cattle compared to hand-collected forage during the winter and spring (December to May), as well as the summer and fall seasons (June to November). Four locations were utilized to represent variation in the Florida pasture landscape, the locations included: Range Cattle Research and Education Center, Ona; USDASubt ropical Agricultural Research Station, Brooksville; Santa Fe River Ranch Beef Unit, Alachua; and North Florida Research and Education Center, Marianna. Forage availabilities (FA) were visually assigned to selected pastures, as either HIGH or LOW, to represent differences in forage quantity between pastures at each location. Fora ge and masticate samples were co llected from each of the four locations from December 2006 to November 2007. Samples were analyzed to determine forage mass, in vitro digestible organic matter (IVDOM ), crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF) concentrations. Selection in dices (SI) were also

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13 determined for each chemical analysis. Hand shears were used to cut the forage to an approximate height of 3.5 cm within a 0.25-m qu adrat; masticate samples were collected using eight ruminally fistulated steer s (two steers/ location). During the winter and spring, masticate samples consistently had greater ( P <0.001) IVDOM concentration (mean=59.1%) and CP concentration (mean=12.3%) compared to handcollected forage samples (45.8% IVDOM; 10.5% CP ). Concentration of IVDOM and CP of masticate and forage samples was also affected by month (P <0.001) resulting in a type x month effect for IVDOM and CP concentration (P <0.001 and P =0.02, respectively). Selection indices of IVDOM differed between FA ( P =0.04) and month ( P <0.001). The SI for IVDOM within the LOW FA was 10% greater compared to the HIGH FA. The selection index for CP concentration was also affected by FA ( P =0.01) and month ( P =0.03). The SI for CP within the LOW FA was nearly 20% greater than that for the HIGH FA. This indicates the steers were more selective of forage material within th e LOW FA compared to the HIGH FA for IVDOM and CP concentration during the winter and sp ring. During the summer and fall, masticate samples consistently had greater ( P <0.001) IVDOM concentration (mean=60.8%) and CP concentration (mean=11.2%) compared to handcollected forage samples (51.7% IVDOM; 9.6% CP). Concentration of IVDOM and CP of masticate and forage samples was also affected by month ( P <0.001) resulting in a type x month effe ct for IVDOM and CP concentration ( P =0.08 and P< 0.001, respectively). Selection indices fo r IVDOM did not differ between FA ( P =0.48) or month ( P =0.43). However, the steers selected forage material that was nearly 19% greater in IVDOM concentration compared to hand-collected forage samples. The selection index for CP concentration was also not affected by FA ( P =0.72) or month ( P =0.16). However, the steers selected forage material that was 20% greater in CP concentrat ion compared to hand-collected

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14 forage samples during the summer and fall. Throughout the year, steers will selectively graze bahiagrass forage that is greater in IVDOM and CP concentration compared to forage collected by hand-sampling, thus influencing supplementati on recommendations for cow-calf producers.

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15 CHAPTER 1 INTRODUCTION Southeastern U. S. cattle production is prim arily involved with cow-calf production systems (Ball et al., 2002). In 2007, there we re approximately 950,000 beef cows in Florida (USDA, 2007). Florida pastures are comprised primarily of tr opical and subtropical forages, which are typically high yielding, but low in quality (Skerman and Riveros, 1990). Tropical and subtropical grasses are reported to contain more cell wall constituents and are less digestible than temperate grasses (Minson and Mcleod, 1970; M oore and Mott, 1973; Barton et al., 1976). Bahiagrass ( Paspalum notatum ) occupies approximately one million hectares within Florida and is the primary component of diets of grazing cat tle in the state (Chambliss and Sollenberger, 1991). As with many tropical grasses, bahiagrass ha s been reported to be low in nutritive value, as determined by hand-harvested samples (Brown et al., 1976); however, this data does not account for the ability of cattle to selectively gr aze within a pasture. Previous research has shown that cattle selectively graze when adequate forage is available for grazing (Weir and Torrell, 1959; Fontenot and Blas er, 1965; Jung et al., 1989; Russell et al., 2004). Other research has illustrated that hand-sampled forage is inacc urate in its estimation of the forage selected by grazing animals (Kiesling et al., 1969; Coleman and Barth, 1973; Skerman and Riveros, 1990). If cattle select forage that is greater in nutritive value than ha nd-harvested samples indicate this may affect supplementation strategies for pr oducers. The purpose of this study was to characterize the nutritive value of bahiagrass fr om four locations acro ss the state of Florida during the winter and spring comparing samp ling techniques, either by hand-sampling or collection of masticate sample within pastures of varying levels of fora ge availability.

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16 CHAPTER 2 LITERATURE REVIEW Predominant Florida Forages According to Burns (2006), the rum inant industry in the Southeast is nearly 100% dependent on grasslands for production. Flor ida is comprised primarily of tropical and subtropical, perennial, warm-season forages, whic h are typically low in quality, yet yield high quantities of DM (Skerman and Riveros, 1990). Climatic conditions are the primary determinant of plant species adaptation and temperature and ra infall are the most critical climatic aspects of plant growth (Ball et al., 2002). Average te mperatures in Florida range from 3 to 37o C while annual rainfall amounts can vary from 97 to 170 cm (NOAA, 2008). Florida soils are classified as sandy, very acidic, low in nut rient-holding capacity, with very little organic matter, and a highly variable water table which can be difficu lt for forage persistence (Villapando and Graetz, 2001). Warm-season grasses of tropical or subtropical origin have a primary growing season of late spring to early autumn (B all et al., 2002). Jones et al (1985) described warm-season, C4 grasses, as generally lower in forage quality (as defined by crude protein [CP] and in vitro digestible organic matter [IVDOM] concentrations) than temperate grasses due to low leaf:stem ratios, rapid maturity rates, and chemical a nd physical characteristics associated with the C4 photosynthetic pathway. Brown (1985) reported that C4 grasses have greater N use efficiency, thus they have greater dry matter yiel ds and are more competitive than C3 grasses, especially when the both forage types are grown on soils with low N content. Bahiagrass (Paspalum notatum) bermudagrass (Cynodon dactylon) and limpograss (Hemarthria altissima) are three of the most important warm-season perennial grasses utilized by Florida cow/calf producers within their cattle grazing systems (Arthington and Brown, 2005).

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17 Bahiagrass Bahiagrass originated in the South Am erican countries: Urug uay, Paraguay, Argentina, and Brazil, and was brought to America in the early 1900s (Chambliss and Sollenberger, 1991). Pensacola bahiagrass ( Paspalum notatum cv. suarae Parodi) is the most widely grown cultivar in the Southeastern region of the United States (Beat y et al., 1968; Gates et al., 1999; Gates et al., 2001). It was introduced into Florida in 1936 (Burton, 1967), and occupies approximately one million ha in Florida ( Chambliss and Sollenberg er, 1991; Stewart et al., 2007). Bahiagrass is drought tolerant and best adapted to sandy soils, but will also grow on poor ly drained soils (Ball et al., 2002; Chambliss a nd Sollenberger, 1991). The 2000 Beef Cattle Nutrient Requirement Council (NRC) reported bahiagrass with 30% dry matter (DM) as having 54% total digestible nutrients (TDN) and 8.9% CP concentration. Fike et al. (2003) reported an equation converting TDN of Tifton 85 bermudagrass ( Cynodon dactylon x. C. nlemfuensis cv. Tifton 85) and Flor igraze rhizome peanut ( Arachis glabrata cv. Florigraze) to in vitro digestible organic ma tter (IVDOM), which is useful since IVDOM is quantified in the lab, bu t TDN is not. The form of the equation is %TDN=[(IVDOM, % x 0.49) + 32.2] x organic matter (OM) concentration. Thus 54% TDN for bahiagrass (NRC, 2000) can be converted to 57.6% IVDOM. Brown et al. (1976) reported digestib le dry matter (DDM) concentrations for Pensacola bahiagrass rang ing from 55-66% (mean=59% DDM) and mean CP concentration of 14% CP from May to October. Chambliss and Sollenbe rger (1991) reported the greatest nutritive value of bahi agrass with a range of 48-68% IVDOM concentration and 4-22% CP concentration from April to September. Low forage IVDOM is an important factor that can negatively impact animal performance, thus forage s need to be properly analyzed to accurately predict animal performan ce (Duble et al., 1971).

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18 Chambliss and Sollenberger (1991) described bahiagrass as a good, general use pasture grass that can withstand drought and heavier grazing pressure than other common pasture grasses. Stanley et al. (1977) supported previ ous rancher experience th at cattle performance would be satisfactory when heav ily grazing bahiagrass pastures, wh ile lightly or infrequently grazed pastures can negatively affect performan ce due to increased maturity of the forage. Bahiagrass is reported to produce 86% of its total a nnual forage mass during the summer (April to September; mean=11,200 kg/ha), while forage mass during the winter period (October to March) produced only 1,800 kg/ha (Mislevy and Ever ett, 1981). Pate (1992) described the major advantage of bahiagrass as its persistence, even with little to no management. Stanley et al. (1977) stated excellent bahiagrass persistence with a high tolerance for prolonged and intense defoliation without concern for comp lete loss of the forage stand. As reported by Sampaio et al. (1976), bahiagrass is not likely to be eradicated by grazing or mowing, t hus management should focus on producing young, vegetative growth that is greater in digestibility without concern for complete loss of stand with increased grazing or mowing. Bahiagrass can maintain 1 to 2 animals units per acre from approximately mi d-March to mid-November with forage mass ranging from 270 to 6,215 kg/ha from April to late September (Chambliss and Sollenberger, 1991). Beaty et al. (1968) reported forage mass signif icantly less than Chambliss and Sollenberger (1991) from June to October (1,058 to 1,366 kg/ha), however with N fertil ization rates of 336 kg N/ha, greater forage mass were achieved (2,148 to 4,236 kg/ha) in the same time period. While bahiagrass can persist in soils that are low in fertility, previous research (Ball et al., 2002; Chambliss and Sollenberger, 1991; Kalmbacher and Wade, 2003; Pate, 1992) described bahiagrass as responsive to N fertilization. However, while Stewart et al. (2007) also stated that

PAGE 19

19 bahiagrass pastures are responsiv e to fertilization, they conc luded that large increases in fertilization intensity are uneconomical when comparing cattle performa nce to input costs. Bahiagrass total N concentration increased as N fertilization increased from 0 to 157 kg of N/ha/cutting); it doubled in forage mass during all harvests from June to September (769 to 1,479 kg/ha/cutting) when fertilization rates of 0 to 78 kg of N/ha/cutting were applied to the forage (Johnson et al., 2001). However, bahi agrass forage mass was the greatest at the fertilization rate of 78 kg of N/ha/cutting but IVDOM concentration of bahiagrass was unaffected by N fertilization (Johnson et al., 2001) Thus applying N fertilization rates greater than 78 kg of N/ha/cutting will not promote greater bahiagrass growth or improve its digestibility, but will increase its total N concentration. Recommendations on the proper amount of N fe rtilization for bahiagrass pastures depend on soil nutrient levels and economic for produ cers (Kidder, 1991). The minimum recommended N application rate of 55 kg of N/ha for grazed bahiagrass pastures recognizes that N is usually the most limiting nutrient in bahiagrass pastur es and when applied once in the spring, the fertilizer will provide enough N for adequate fora ge growth to maintain beef cattle during the summer (Kidder, 1991). Whereas, the maximum r ecommended fertilization rate of 179 kg of N/ha would allow maximum bahiagrass producti on (Kidder, 1991). However as reported by Johnson et al. (2001), N fertiliza tion application rates greater th an 78 kg of N/ha/cutting will not be effectively utilized by th e forage and may be unprofitable. A single application of N fertilization during the spring, rega rdless of application rate, is recommended for bahiagrass, as opposed to split application in the spring and late summer, to increase the total N concentration of the forage, due to economic return of the N input. This will benefit the breeding herd, which

PAGE 20

20 will be lactating and needing to gain weight in order to increase the success of rebreeding (Kalmbacher and Wade, 2003). Drought can negatively affect bahiagrass popul ations by slowing or stopping biological processes, including decreased l eaf expansion, increased mature leaf senescence, and reduced tillering (Jones, 1985), thus reducing forage ma ss production. However, IVDOM and CP may increase in drought-stressed plants due to increases in soluble carbohydrates and N concentrations in the leaves (B all et al., 2002; Burton et al., 1957). Temperature can also be an important factor to tropical a nd subtropical species whose optim um temperatures range from 3935oC; however forage mass significantly decreases at 24oC and little growth occurs at 10oC (Ball et al., 2002). Bermudagrass Berm udagrass originated in Sout heastern Africa (Ball et al., 2002) and is the second most planted, improved, warm-season, perennial grass in Florida (Newman, 2008). Bermudagrass is typically used for pasture and hay production wi thin Florida because of its persistence under heavy grazing, highly efficient response to N fe rtilization, and high forage mass (Chapman et al., 1972; Ball et al., 2002; Chambliss et al., 2006; So llenberger, 2008). Accord ing to Sollenberger (2008), bermudagrass is best adapted to moderately to well-drained so ils and is considered relatively drought tolerant. However, Newman ( 2008) stated that bermudagrass is adapted to soils ranging from fertile sandy loam to sand to clay, but agrees with Sollenberger (2008) that bermudagrass is best suited to well-drained site s and is drought tolerant The primary growing season of bermudagrass in Florida is from May to October (Ball et al., 2002). Common bermudagrass is a common pasture gr ass in the Piedmont and Coastal Plains regions of the Southeastern United States (Adams et al., 1967). However, the Coastal bermudagrass hybrid has proven to be superior to common bermudagrass in terms of forage mass

PAGE 21

21 (Adams et al., 1967), but not in N or crude fiber concentrations (Adams and Stelly, 1958; Miller et al., 1961; Adams et al., 1967). Dry matter yields of non-fertilized common bermudagrass have been reported at 2,331 kg/ha from April to September, while non-fertilized Coastal bermudagrass had forage mass of 5,156 during th e same time period (Adams and Stelly, 1958). Bermudagrass hybrids (Alicia, Hardie Midland, and Tifton 44) were evaluated (Taliaferro et al., 1987) for nutritive value with mean IVDOM con centration of 41.6% and 9.5% CP concentration during the winter (November to Februa ry). Jolliff et al. (1979) decl ines in in vitro digestible dry matter (IVDDM) and CP of Coastal and Coastcro ss-1 bermudagrass variet ies with increasing maturity, while the NDF and ADF concentrations increased. In a study by Guerrero et al (1984) using bermudagrass dige stibility to predict animal gains, it was determined that while forage mass was abundant from May to October (mean=92.4 g DM/ kg live weight/ day), IVDMD concentr ation was insufficient (mean=56.9%) to meet nutritional requirements of grazing cattle. A curvilinear relationship between gain and available forage was reported (Guerrero et al., 1984); the parameters of bot h slope and the asymptote of the curve increased in magnitude as IVDMD increas ed, thus less available forage was required to optimize gain. Minson and McLeod (1970) reported that IVDDM concentrations of less than 65% are inadequate for cattle grazing tropical grasse s as the sole diet. Th erefore, cattle would have to selectively graze the forage to maximize performance since it would be physically impossible for the steers to consume enough forage to meet their requirements on a daily basis. As stated by Guerrero et al. ( 1984), an improved method of classify ing forage relative to grazing animals is needed to improve the relationship be tween animal gain and available forage. Thus justifying the purpose of this study by illustrating th e need for classification of the differences in forage chemical composition between hand-coll ected forage and masticate samples.

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22 The economic benefits of grazing cows on fe rtilized bermudagrass were evaluated by Neville and McCormick (1976) who determined that when using bermudagrass forage as the only feed source, it was more profitable to ferti lize pastures at lower ap plication rates (152 kg of N/ ha) compared to more heavily managed past ures (322 kg of N/ ha) under favorable weather conditions. Cows had greater ADG (2.44 kg/ha) and greater saleab le calf weight (410 kg/ha) when grazed on bermudagrass pasture that received the greater fertilization compared to values for the lower fertilizat ion rate (ADG=1.88 kg/ha; saleable calf weight=328 kg/ha; Neville and McCormick, 1976), but after considering land, capital, labor, management, and other input costs, the lower fertilization treatment was the most profitable to the producer. Limpograss Lim pograss is native to South Africa, sp ecifically the Limpopo River area, and was introduced into Florida in 1967 (Kretschmer and Snyder, 1979). Limpograss has been described as best adapted to acidic soils, fertile or fertilized sand to clay soil types. It is better adapted to flatwoods than well-drained sands, and highly ad aptive to flooded area s (Quesenberry et al., 1987; Newman, 2008). Limpograss is typically us ed for grazing, hay, and stockpiling (Pate, 1992; Newman, 2008). Stockpiling is defined as a standing hay crop used for grazing cattle after the primary forage growing phase has ceased (Sollenberger et al., 2006). Stockpiling is a common practice for limpograss compared to bahiagrass or bermudagrass due to its superior digestibility, even with increased maturity (Quesenberry and Ocumpa ugh, 1980; Davis et al., 1987; Pate, 1992; Sollenberger et al., 2006). However, while limpograss digestibility remains significant during late fall and ea rly winter, CP concentration is generally low and cattle should be supplemented with a protein supplement to improve animal performance (Rusland et al., 1988; Holderbaum et al., 1992; Brown and Adjei, 2001; Sollenberger et al., 2006). Brown and Adjei (2001) indicated that limpograss IVDOM concentrations of the total canopy can range

PAGE 23

23 from 34-44% from July to November. Sollenbe rger et al. (2006) de scribed limpograss IVDOM concentrations ranging from 40-70% during the year which includes early spring growth as well as mature, stockpiled grass. This range is consis tent with the results of Kretschmer and Snyder (1979). Crude protein concentrations of limpogr ass are reported to vary from 3-10% during March to July (Quesenberry and Ocumpaugh, 1980; Brown and Adjei, 2001; Sollenberger et al., 2006). Pitman et al. (1994) reported that lim pograss CP and IVDOM concentrations were 2% and 5% greater from pastures w ith high stocking densities (8 steer s/ha) than pastures with lower stocking densities (4 steers/ha) during the summer. Cattle ADG on limpograss pastures has been repo rted (Sollenberger et al., 1989) to be greatest in the spring (mean=0.50 kg/d), while ADG declined with increasing forage maturity. Low CP concentrations are also found during the fall and winter, thus negatively impacting cattle performance. However, cattle performance can be positively affected by the addition of N to limpograss, whether through N fertilization of the forage (Kretschmer and Snyder, 1979; Davis et al., 1987; Sollenberger et al ., 1989), addition of legumes (R usland et al., 1988), ammoniation of limpograss hay (Brown et al., 1987), or throug h protein supplement fed to the herd (Pate, 1992; Brown and Adjei, 2001; Arthington and Brown, 2005; Sollenberger et al., 2006). Davis et al. (1987) reported no differences in limpograss ADF or NDF concentration (37 to 39% ADF and 63 to 67% NDF) from December to April, but their IVDDM concentrations never reached 65%, which has been determined to be the minimum IVDMD threshold for ca ttle grazing tropical grasses (Minson and McLeod, 1970). Milford and Haydock (1965) reported that the minimum level of CP concentration needed for maintenanc e of dry cows grazing trop ical grasses to be no less than 7.2% CP. However, CP concentration of limpograss (Davis et al., 1987) increased from a minimum of 7.0% to a maximum of 15.5% CP from December to April as N fertilization

PAGE 24

24 application increased (0 kg/ha to 400 kg/ha; Da vis et al., 1987), thus illustrating the positive effect of N fertilization on CP concentration. Rusland et al (1988) reported greater ADG in steers grazing limpograss pastures over-seeded w ith aeschynomene compared to steers grazing limpograss pastures fertilized with 50 kg N/ ha (0.70 kg/d and 0.39 kg/d, respectively). The previous studies conclude that with the addition of N to tropical grass pastures, improvements in ADG can be expected, which can prove to be useful since tropical grasses are reported to be low in CP and digestibility du ring much of the year. Comparison of Florida Forages While bahiagrass is the most commonly used pasture forage in Florida (Cha mbliss and Sollenberger, 1991), there are often distinct diffe rences among the predominant forages used in Florida. Duble et al., (1971) repor ted that the primary factor aff ecting animal performance is the chemical composition of the standing forage when adequate forage is available for grazing. In a grazing evaluation of perennial gr asses in Florida using yearling steers (Pitman et al. 1984), there were no differences in ADG among stargr ass (ADG=0.40 kg/head), bermudagrass (ADG=0.36 kg/head) and limpograss (ADG=0.40 kg/head) during cooland warm-seasons (November to August). In a study by Arthington and Brown (2005), limpograss contained the lowest CP concentration after 4 and 10 weeks of regrowth (8.5% and 6.0% CP, respectively) compared to bahiagrass (10.0% and 7.0% CP, respectivel y) and bermudagrass (11.0% and 7.0% CP, respectively). Bahiagrass had the lowest mean NDF concentration (79.0%) at compared with the other grasses (bermudagrass=84.1%; limpograss=86.3 %) and it was also the only forage that did not have a greater NDF concentration after 10 to 4 wk regrowth. Limpograss had the greatest ADF concentration (46.0%) in comparison to the other grasses (bahiagrass=40.0%; bermudagrass=43.8%). Arthington and Brown (2005) also reported a decrease in IVDOM concentration from 4 to 10 wk regrowth for bermudagrass (53.9% and 44.1%, respectively), but

PAGE 25

25 not bahiagrass (52.4% and 51.3%, re spectively). The authors conc luded that bahiagrass was the most favorable tropical grass for cattle compar ed to bermudagrass and limpograss due to low NDF and ADF concentrations, greater IVDOM and CP concentrations, and greater retention of nutritive value regardless of time of regrowth. Mislevy and Everett (1981) reported that Pe nsacola bahiagrass produc ed of 86% of its annual forage mass from April to September, while bermudagrass produced 73% of its annual forage mass in the same time period, indicating the possibility for grazing bermudagrass longer into the fall and winter compared to bahiagrass. In a study by Johnson et al. (2001), unfertilized bahiagrass had greater forage mass (769 kg/ha) compared to unfertilized bermudagrass (656 kg/ha), however with increased N fertilization rates (0 to 157 kg N/ha/cutting), bermudagrass was consistently greater in forage ma ss (mean=1,756 kg/ha) compared to bahiagrass (mean=1,429 kg/ha). Bertrand and Dunavin (19 85) stated that beef steers consuming bermudagrass cultivars (Callie, Tifton 72-81, Tifton 72-84) gained faster (0.49 kg/head/day) than steers grazing Pensacola bahiagrass (0.37 kg/head/d ay); bermudagrass also had greater forage mass (11,148 kg/ha) than bahiagrass (8,824 kg/ha). Utley et al ., (1974) reported that forage mass of Coastal and Coastcross-1 bermudagras es was nearly 35% greater (22,192 kg/ha) than Pensacola bahiagrass forage mass (15,467 kg/ha) when measured from May to October; bermudagrass also produced greater ADG of st eers (0.72 kg/d) compared to bahiagrass (0.49 kg/d). Thus from the reports by Bertrand and D unavin (1985) and Utley et al. (1974), it can be concluded that bermudagrass will produce greate r cattle and forage performance compared to bahiagrass. Sollenberger et al. (1989) compared steer performance while grazing either Floralta limpograss or Pensacola bahiagrass pastures, ADG were reported to similar for both forage species from July to November (mean=0.41 and 0.38 kg/d, respectively). Mean limpograss

PAGE 26

26 IVDOM concentration (60.4%) was greater than bahiagrass (55.0%), but bahiagrass had greater CP concentration (11.0%) than lim pograss (7.0%) in the same time period (Sollenberger et al., 1989). It can be concluded from this study that ADG may not differ between limpograss and bahiagrass (Sollenberger et al. 1989). These resu lts may be attributed to chemical composition of the forages; while limpograss had greater I VDOM concentration, bahiagrass had greater CP concentration thus possibly equating the valu e of the forages when measured as gains experienced by the animal. Tropical grasses have been reported to be low in IVDOM and CP concentrations with greater NDF and ADF concentrations compared to temperate grasses, while their forage mass is abundant for much of the year. Thus manageme nt of the forages should involve proper sampling to ensure correct evaluation of the nutritive value of the pastures to minimize nutrient deficiencies when comparing forage nutri ent supple to beef cattle requirements. Beef Cattle Nutritional Requirements The prim ary objectives of commercial cow-ca lf producers are to maintain the cow while maximizing profitability, obtain efficient repr oduction rates, and attain high calf weaning weights (Ball et al., 2002). Nutrition is the most significant factor influencing the cow-calf producers objectives (Kunkle et al., 2002). Nutritional requireme nts can be characterized in several specific ways: energy, pr otein, minerals, vitamins, a nd water (Ensminger, 1987; Kunkle et al., 2002). The nutritional re quirements for maintenance are considered to be the most important requirements and should be met befo re other production re quirements (Cullison, 1975). Various factors affect ma intenance requirements such as body weight, breed or genotype, sex age, season, temperature, physiological state, and previous nutrition (NRC, 2000).

PAGE 27

27 Factors Affecting Requirements Cassard and Juergenson (1971) stated that en ergy is the m ost important consideration when feeding livestock. Protein should be fed to meet maintenance requirements since protein fed in excess of an animals needs will be deaminat ed in the liver and used as a source of energy by the animal (Cullison, 1975). As reported by Ferrell and Jenkins (1984 a), approximately 70% of the energy required to maintain the non-pregnant, non-lactating cow herd can be attributed to energy costs for maintenance and, about 50% of the total feed energy required for beef production is for maintenance. Cullison (1975) defines maintenance as the maintaining of an animal in a state of well-being or good health from day to day and a maintenance ration is defined as the feed required to adequately support an animal doing no non-vital work, not growing, developing no fetus, storing no fat, or yielding no product. Ho wever, the NRC (2000) defines the maintenance requirement for energy as the amount of feed energy intake that will result in no net loss or gain of energy from the tissues of the animal body. The processes or functions comprising maintenance energy requ irements include body temperature regulation, essential metabolic processes, and physical activity (NRC, 2000). Age, body weight (BW), body condition score (BCS), sex, stage of production, environment, dry matter intake (DMI) and breed are some of the factors that in fluence cow energy requirements. Metabolizable protein (MP) is used by the 2000 Beef Cattle N RC as the estimate for protein required by cattle because it accounts for rumen degradation of protein and id entifies the requirements of gastrointestinal microorganisms, as well as the animal. Metaboliz able protein is defined as the true protein absorbed by the intestine, as supplied by microbial pr otein and undegraded in take protein (NRC, 2000). Factors which can affect metabolizable protein requirements are metabolic fecal N, urinary N, and scurf losses, but also include the previously mentioned fact ors that also influence energy requirements.

PAGE 28

28 Age is a known variable influencing ener gy and protein maintenance requirements; however the primary influencing factor may be correlated more closely to weight and BCS than physiological age. An equation by Corbett et al. (1985) indicates energy maintenance requirements decrease by 3% per year. This co ncept is also supported by the work of Van Es (1972), which stated that for very young gr owing cattle (<100 kg), energy maintenance requirements appear to be greater than those for older animals. However, Vermorel et al. (1980) indicated that maintenance requirements of cattle changed little between 5 and 34 weeks of age. Neville, Jr. (1971) also reported that age does not affect the en ergy requirements of lactating Hereford cows. Thus there are more important factors influe ncing maintenance requ irements besides age alone. Sex class is also a consideration when determining maintenance requirements for energy and protein. Assuming cattle are of a similar genotype, there is a 15% greater maintenance requirement for energy for bulls compared to steers or heifers (NRC, 2000). However Chizzotti et al. (2008) concluded that there were no differences in energy or protein required for maintenance between Nellore or Nellore x Bos taurus bulls and steers or heif ers. Chizzotti et al. (2008) is also in agreement w ith the results of Chizzotti et al. (2007) which reported no differences for energy or protein required for maintenance between F1 Nellore x Red Angus bulls, heifers, or steers. There are conflicting results as to the influence of BW on maintenance energy requirements. Lofgreen and Garrett (1968) and T honney et al. (1976) reported that maintenance requirements of beef cows within specific stag es of production and sim ilar environments are dependent primarily on BW. Lofgreen and Garre tt (1968) stated that as metabolic body weight (W0.75=average empty BW) increases, the fasting heat production is increased and can result in

PAGE 29

29 an increase in maintenance energy requirements. In contrast, Geay (1984) reported an apparent decrease in maintenance requirements as live wei ght increased in Charolais and Fresian bulls. Geay (1984) reported that for every 100 kg incr ease in BW, the metabolizable energy required for maintenance decreased by 3 kcal/W0.75 for Charolais bulls and 10.5 kcal/ W0.75 for Fresian bulls. Tyrell and Moe (1980) al so reported a 13 to 18 kcal/ W0.75 decrease in metabolizable energy required for maintenance for Hereford heif ers. While breed differences influenced the amount of energy required for main tenance, these results indicate th at as weight increases, the metabolizable energy required for maintenance decreases. Additionally, studies by Klosterman et al. (1968) and Thompson et al. (1983) suggest that an increase in BW due to increased fat deposition does not necessarily increase main tenance energy requirements. However, Houghton et al. (1990) compared 128 pregna nt, mature Charolais x Angus co ws, reported that when energy was expressed as total daily predicted mainte nance energy, fatter cows (BCS=4) required 21% more energy than cows in moderate condition (BCS=3) during the last trimester of pregnancy. According the NRC (2000), energy requirements ar e calculated based on metabolic BW, thus a cow with increased BW w ould have increased maintenance energy requirements. Therefore, BW alone cannot be used to accu rately predict the en ergy requirements of larger breeds (Hereford, Angus x Hereford, Charolais x Herefor d, and Brown Swiss x Hereford) with greater milk production pot ential (Lemenager et al., 1980). A model proposed by Lemenager et al. (1980) predicted TDN requirements from two yearly trials and initial lactation cow BW; initial lactation cow BW was an importa nt factor in the e quation accounting for 60.5% of the variation (r2=0.60). But in a second model by Lemena ger et al. (1980), trial year, initial lactation cow BW, BCS at star t of lactation phase; cow weight and BCS accounted for more variation (r2=0.81) than BW alone. In a third mode l estimating TDN required during lactation

PAGE 30

30 proposed by Lemenager et al. (1980) which includ ed trial year, initial lactation cow BW, initial BCS and estimated milk production; the estimated milk production was an important factor while BW ( P <0.14) and BCS ( P <0.25) were not. However, initial cow BW, initial BCS and estimated milk production accounted for nearly all variation (r2=0.98) in the estimated TDN requirements during early lactation (Lemenager et al., 1980). Thus BW alone should not be used to predict energy requirements, but when BW, BCS and estimated milk production are combined, a more accurate prediction of energy requirements can be established. Houghton et al. (1990) also reported that some indicator of BCS needs to be used in combination with BW or BW plus milk production to estimate the levels of energy needed to maintain beef cows during late gestation and early lactation. Previous plane of nutrition and energy intake are also factors when estimating maintenance energy requirements. According to Fox et al. (1972) who used Hereford steers, adjusting maintenance requirements for previous plane of nutrition is more biologically accurate when projecting gains over an entire feeding period of approximately 180 days compared to the measurement of compensatory gain s experienced in the first 2 to 3 months of a feeding period. In a study by Houghton et al. (1990), two en ergy level regimes (low energy70% NRC requirement and maintenance energy100% N RC requirement) were fed prepartum to 128 mature, pregnant Charolais x Angus cows. At th e initiation of the trial, no differences were observed between the cows from either treatments. However, at parturition, cows on the maintenance energy intake had at least 0.5 grea ter BCS and 40 kg greater BW than those on the low energy feeding level. These results are si milar to those from Bi rkelo et al. (1991) who reported that a high plane of nutrition caused a consistent increase in fasting heat production (7%) and maintenance metabolizable energy (14%) in Hereford steers compared to steers on a

PAGE 31

31 low plane of nutrition. Papas (1977) determin ed that non-lactating, non-pregnant ewes are responsive to increased N in the diet, whether by protein or non-prot ein N supplement, when provided at levels greater than required for ma intenance. Carroll et al. (1964) used 40 weanling heifers to determine the effects of a low-protein diet (37% of protein re quired for maintenance) on total gain, heifers consuming a low-protein di et were negatively impacted (0.27 kg total gain/ heifer) compared to heifers receiving adequate dietary protein for ma intenance (12.25 kg total gain/ heifer). Thus consideration must be made to previous and current planes of nutrition when adjusting cow energy and protei n maintenance requirements. The stage of production is an important factor to consider when calculating cow energy maintenance requirements since there will be in creased heat production during fetal growth and milk production. NRC (2000) stat es that, based on previous research values, maintenance requirements of lactating cows are approximately 20% greater than those of non-lactating cows. In a study by Neville and McCullough (1969) using 20 lactating, non-pregnant and 8 nonlactating, non-pregnant Hereford cows, it was re ported that lactating co ws have 30% greater maintenance requirements than non-lactating, nonpregnant cows. However, in a later study by Neville (1974) comparing 40 non-lactating and 24 lactating Hereford cows, it was determined that the energy maintenance requirements for lactating cows are 39 to 41% greater than for nonlactating cows. The variation between Neville and McCullough (1969) and Neville (1974) may have been affected by diet and differences in the amount of TDN provi ded during the feeding trials. While greater requirements for lactati on have been established, there have also been studies designated to understand ing the requirements of other stages of production, such as gestation. Montano-Bermudez et al. (1990) concluded that ener gy requirements for gestation were lower than requirements for lactation. In two gestation trials (Montano-Bermudez et al.,

PAGE 32

32 1990) utilized 71 and 77 first cross cows, respec tively, from Hereford, Red Poll, and Milking Shorthorn sires and Angus dams, the results from the first trial indicated that the energy requirements associated with gestation were 86.5% of the requirements for lactation. Whereas in the second trial (Montano-Bermud ez et al., 1990) maintenance ener gy requirements for gestation were 78% of the requirements for lactation. Di fferences in BCS, BW, and genetic variation of the cows were used to account for the maintenance requirement differences between the two studies by Montano-Bermudez et al. (1990). Overal l, it was concluded that the cattle with greater milk production (Milking Shorthorn x Angus ) had the greatest maintenance requirements. While gestation requires increased energy for main tenance, there are differe nces in the amount of energy required depending on the stage of pregna ncy. The energy required for gestation is initially very small, only 0.1% of the energy requirement during the third month postpartum Hersom, 2007). In contrast, the ge station energy requirement one month prior to parturition is approximately 56% of the total energy require ment (Hersom, 2007). Wa rrington et al. (1988) showed that maintenance metabolizable energy requirements increased by 25% as gestation progressed for two-yr old, pregnant heifers. It can be conclude d that maintenance requirements for gestation are greater than those for non-pregnant cows and requirements for lactation are greater than requirements for gestation. Differences between breeds also affect main tenance requirements. Dairy breeds are known to have greater maintenance requirements (G arrett, 1971; Holloway et al., 1975; Thompson et al., 1983), compared to beef cattle breeds. The 2000 Beef Cattle NRC estimates that approximately 20% greater maintenance energy is required for dairy breeds compared to beef breeds; however, within beef breeds, Bos indicus breeds are reported to re quire 10% less energy for maintenance compared to Bos taurus breeds due to genetic potential for productivity (NRC,

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33 2000). Solis et al. (1988) stated that geneti c, environmental, physiological, body composition, and nutritional aspects must be considered in maintenance requirements for cows of different breeds. Also, Solis et al. (1988) reported that so me cattle types may be better suited for survival on feed of lower quality than other breeds. This is crucial for Florida cows, which are maintained on low-quality forages. The cattle ty pes (dry, mature, non-pregnant cows) with the lowest maintenance requirements in the trial by Solis et al. (1988) were the Angus x Hereford and Brahman x Hereford crosses (89 and 92 kcal/W0.75, respectively), while the purebred cows (Angus, Brahman, and Hereford) had greater, si milar mean maintenance energy requirements 102 kcal/W0.75. The lower maintenance requirements of Brahman cows were attributed to the lower quantities of internal fat and smaller metabolically active organs usually found in Brahman cattle. This is helpful in Florida cow-calf breeding operations since Brahman genetics are commonly utilized due to increase d heat and pest tolerance. Fe rrell and Jenkins (1998) reported that the net energy required fo r maintenance differed between Bos taurus (mean=98.3 kcal/kg0.75/d) and Bos indicus (mean=110.4 kcal/kg0.75/d) sired breeds. However, in a study by Chizzotti et al. (2008) establis hing protein and energy requiremen t of Nellore and Nellore-cross cattle, it was determined that there were no diffe rences in required maintenance energy between breeds (Nellore, Nellore x Angus, Nellore x Red Angus, Nellore x Simmental, Nellore x Limousin, and Nellore x Brangus). Also, there was no difference for net protein required for maintenance between breeds (Chizzotti et al., 2008). However, it a study by Thompson et al. (1983) comparing 20 Angus x Hereford and 20 Angus x Holstein five-yr old cows, it was determined that Angus x Hereford cows had greater protein maintenance requirements compared to Angus x Holstein cows, which may have been due to breed type and BCS differences. The

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34 results of Chizzoti (2008) may be different from other research due to the influence of the Nellore breed in the crossbred cattle. Environment can greatly affect maintenance re quirements of cattle with temperature as one of the leading factors affecti ng requirements (Fuquay, 1981). Extrem e heat and cold can affect maintenance requirements since cattle will need to either dissipate or increase body heat production to maintain homeostasis. Flor ida cattle may not expe rience extreme cold environments, as experienced by Northern and Mi dwestern cattle; however heat tolerance is necessary for Florida cattle due to the subtropical climate of th e state. Hammond et al. (1998) discussed the importance of heat tolerance in cattle within tropical or subtropical conditions; it was determined that the relationship to feed intake or, under grazing conditions, grazing time of cattle is primarily affected by heat tolerance. Declining feed intake has been a cause of decreased milk production in dairy cows (Wayman et al., 1962). This is important for cow-calf production systems since calf wei ghts may be affected negativel y by decreased milk production. Heat stress also affects maintenance energy requ irements since higher temperatures in cows necessitate use of greater ener gy for dissipating heat (Morrison, 1983). There has also been a tendency for an increase in protein requirement for lambs during times of heat stress (Ames and Brink, 1977). In a study by Delfino and Mathison ( 1991) conducted at the University of Alberta, Canada, 49 Hereford or Herfordcross yearling steers were fed either inside (mean temp=16.90C) or outside (mean temp=-7.60C) from January to April. De lfino and Mathison (1991) concluded that the net energy required for maintenance increas ed by 18% for the steers exposed to the cold winter environment compared to the indoor steers. Plant-Animal Interface Previous r esearch shows that cattle will selectively graze when adequate forage is available for grazing (Weir and Torrell, 1959; Fontenot and Blaser, 1965; Jung et al., 1989; Russell et al.,

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35 2004). Weir and Torrell (1959) used wethers graz ing Northern California native range and other temperate forages to show that sheep selected fo rage that was 4.3% greater in CP compared to hand-collected forage samples. Russell et al. (2004) reported that Simmental cows grazing smooth bromegrass (Bromus inermis) during the summer selected forage material that was greater in IVDMD and CP, and lower in NDF compared to hand-collected forage samples. Similarly, Jung et al. (1989) determ ined wether lambs grazing bromegrass (Bromus inermis) selected forage material with lower NDF concen tration (52% vs 68%), but greater IVDMD (64% vs 52%) and CP (14% vs 8%) compared to hand-sampled forage when samples were taken every 14-d from May to August duri ng a three-yr trial. Other research has illustrated that hand-sampled forage is inaccurate in its estimation of a grazing animals selected diet (Kiesling et al., 1969; Colema n and Barth, 1973; Skerman and Riveros, 1990). Kiesling et al. (1969) reported esophageal extrusa samples of steers contained greater concentrations of ash, protein, silica, and ether extract compared to hand-plucked tobosa grass (Pleuraphis mutica) samples, therefore the hand-coll ected forage samples incorrectly estimated selected forage material. Coleman and Barth (1973) reported esophageal-fistulated steers grazing either tall fescueKorean lespedeza (Festuca arundinacea-Lespedeza stipulacea) or orchardgrass-ladino clover (Dactylis glomerata-Trifolium repens) pastures were selective of forage material that was greater in CP con centration (difference=4.7%), ADF concentration (difference=10.9%) and DDM concentration (diffe rence=2.0%) in comparison to hand-collected forage samples from May to November. If cattle are able to select a diet that is greater in nutritive value than what hand-harvested sample s indicate, this may affect supplementation strategies for producers. In a study by Johnson et al. (1998), it was determined that nutritional deficiencies of grazing cattle n eed to be identified for prope r formulation of supplementation

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36 strategies and decisions in order to optimize animal performance. However, comparison of hand-collected and masticate samples of bahiagrass has not been reported in the literature, thus validating the purpose of this research. While there are noted differences between masticate and hand-coll ected forage nutritive value, there may also be differences between the extrusa samples from esophageal and ruminal fistulated animals. Holecheck et al. (1982) re viewed methods for determining the nutritive value of ruminant diets concluding th at while esophageal fistulated animals are superior to rumen fistulated animals since less labor is involved and diet samples are more representative of actual forage consumed, there are advantages and disadv antages to both fistula types. Some of the main problems associated with esophageal fistul ae sampling are salivary contamination, rumen fluid contamination from eructa tion, use only for grazing studies, and incomplete recovery of selected forage material (Blackstone et al., 1965; Acosta and Kothmann, 1978; Arnold and Dudzinski, 1978). Advantages of ruminal fistulae over esophageal fistulae include easier establishment and maintenance of the fistula, le ss care of the fistulated animal required during collection, use in other experiments besides graz ing trials, and entire collection of sampled forage (Lesperance et al., 1960). However, time needed for emptying and washing the rumen before collection, as well as for returning rume n contents to the animal are disadvantages to rumen fistulas (Lesperance et al ., 1960). Both fistulation tech niques are approved for collection of forage material from cattle, but preference for type of experimental usage is one of the primary determinants of c hoice of fistula type. There may also be differences in DM loss between drying procedures used for masticate and hand-collected forage samples. Mayla nd (1968) reported that oven-drying alfalfa ( Medicago sativa ) at 60, 80 and 1000C led to C, N, and DM losses compared to zero losses by freeze-drying;

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37 however, the differences in C and N losses were less than 1% of the total C or N concentration of the forage. However, Acosta and Kothma nn (1978) concluded that oven-drying (600C) and airdrying (28-350C) were not satisfactory for drying esophageal extrusa samples of post oak savannah range ( Quercus stellata ) and Coastal bermudagrass due to increased OM losses from increased heat and extended dr ying times of the samples. Ho wever, freeze-drying the extrusa samples accurately reflected the nutritive value of the collected forages (Acosta and Kothmann, 1978). There were no differences in CP, acid detergent lignin (ADL), cellulose, or hemicellulose concentrations of the hand-plucked bermudagrass samples between all drying techniques (Acosta and Kothmann, 1978); however, total nonstructu ral carbohydrates were less in the ovenand air-dried hand-plucked bermud agrass samples. Wilkinson et al. (1969) contradict the results of Acosta and Koth mann (1978) since they found greater cell wall components, ADF, and ADL in airand oven-dried hand-clipped Coastal bermudagrass samples compared to freeze-dried samples. Schimd et al. (1970) reported that oven-drying at 60 and 850C was acceptable for determining IVDMD of corn ( Zea mays) and sorghum ( Sorghum bicolor ) fodder and silage and lyophiliz ation resulted in the lowest amount of DDM loss. Thus consideration should be given when determining drying method choice for forage samples. Previous research (Bennett et al., 1999) has shown that when forage mass is not limiting, the main determinant of diet selection by steer s is the chemical composition of the available forage. However, in a range grass grazing study Bailey (1995) reported that steers develop preferences for native range and te mperate forages with greater CP concentrations regardless of the forage quantity available. Guerrero et al. (1984) used bermudagrass digestibility to predict animal gains and determined that while forage mass was abundant from May to October (mean=92.4 g DM/ kg live weight/ day), fora ge IVDMD concentration was insufficient

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38 (mean=56.9%) to meet grazing cattle requirements. Since the steers continuously gained BW during the trial (Guerrero et al., 1984), it was concluded that cattle selectively grazed the available forage because it was physically impossi ble for the steers to consume enough forage to meet their energy requirements, as determined by forage IVDMD concentr ation. Fisher et al. (1991) determined that steers grazing bermudagrass, switchgrass (Panicum virgatum) flaccidgrass (Pennisetum flaccidum) and bermudagrass select fora ge material 16.9% greater in IVDMD concentration and 12.6% lower in NDF concentration when forage mass was not limiting (mean forage mass=1,818 kg/ha) from May to September. This indicates that steers were selective of available forage, as determined by forage chemical composition, during the summer with a mean selection index of 115.4% for all grasses (Fisher et al., 1991). There have not been any studies to date comparing the nutriti ve value of hand-collected bahiagrass to forage material selected by grazing animals. Jung et al. (1989) found that wethers grazing sm ooth bromegrass selected forage material 10% greater in CP concentration compared to pasture samples. Dubbs et al. (2003) reported that CP concentrations of hand-clipped tall fescue were greatest in April (16.5%) and decreased during the remainder of the summer (mean=12.7 %); masticate samples selected by steers averaged approximately 4% greate r CP concentration than hand-collected samples from April to September. Since tall fescue is a cool-season gr ass, the chemical composition will be negatively affected at the end of the spring, as shown by D ubbs et al. (2003), since increased temperatures and solar radiation end the primary growing seas on of cool-season grasses (Ball et al., 2002). Whereas bahiagrass, a warm-season gr ass, will have greatest CP in late spring/ early summer due to low rainfall and vegetative growth state (K almbacher and Wade, 2003). Weir and Torrell (1959) reported that esophageal extrusa samples of native range, as well as temperate grasses and

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39 legumes, had greater CP concentration (mean= 18.0%) than forage samples collected by handclipping (14.7%) during a two-yr study. Bailey (1995) concluded th at in heterogeneous areas of forage (ie. differing forage chemical composition and forage mass within a pasture), cattle will develop preferences for patches of grass with gr eater CP concentration regardless of forage quantity, which is in agreement with previously mentioned research (Bailey et al., 1995; Bennett et al., 1999). Cattle are less selective of NDF compared to other ruminant species (Reid et al., 1990), because of cattles ability to ma intain greater levels of intake of cell wall constituents. In contrast, in a trial by Dubbs et al. (2003), hand-clipped tall fescue samples had 5% greater NDF concentrations compared to masticate samples fr om April and May while forage quantity was at a minimum. Dubbs et al. (2003) also reported that hand-clipped fescue samples averaged 5% greater ADF concentration from April to May co mpared to masticate samples. Thus while fescue was in the vegetative growth state during April and May, steers were selective of forage material with the least proportion of cell wall cont ents even though the forage itself was low in fiber content. However, Norman et al. (2004) concluded that sheep graz ing saltbushes would not show preference for forage material on the basi s on ADF concentration; however, the sheep did select between two saltbush species ( Atriplex amnicola and Atriplex nummularia ) preferring the saltbush variety with greater ADF concentration, wh ich may be attributed to greater palatability of the preferred species since the sheep were not selecting for digestibility, CP, DM, or OM. Previous research has demonstrated differences in the selection by grazing animals of forage based on nutritive value. Thus the proper characterization of th e nutritive value of masticate samples in comparison to the nutritive value of hand-collected forage samples is

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40 necessary to identify possible nutritional deficienci es so that diet supplementation strategies can be properly formulated to optimize animal performance.

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41 CHAPTER 3 EFFECTS OF FORAGE SAMPLING METHOD ON NUTRITIVE VALUE OF B AHIAGRASS DURING THE WINTER AND SPRING Introduction Florida p astures are comprised primarily of tropical and subtropical forages, which are typically low in quality, yet yield high quanti ties of DM (Skerman and Riveros, 1990). Bahiagrass ( Paspalum notatum ) occupies approximately one million hectares within Florida and is the primary component of Florida grazing cattle diets (Chambliss and Sollenberger, 1991). Bahiagrass has a primary seasonal production from April to October, however it can be grazed into the winter if managed prope rly (Ball et al., 2002). Advantag es to providing bahiagrass in a cattle grazing system are persis tence under little to no manageme nt and moderate quality during most of the year. However, a consistently highquality bahiagrass is rarely achieved, regardless of management or fertilizati on, therefore bahiagrass may not be a good forage choice for cattle with greater nutritional requirement s, such as lactating or pregnant animals (Pate, 1992). As with many tropical grasses, bahiagrass has been reported to be low in nutritive value, as determined by hand-harvested samples; however, th is data does not acco unt for the ability of cattle to selectively graze within a pasture. According to the NRC (2000), bahiagrass contains 8.9% CP or less and 54.0% TDN on a DM-basis, whereas beef cow requirements range from 612% CP and 45-65% TDN depending on the weight and physiological state of the cow. Currently, there is very little publ ished data available detailing changes in bahiagrass chemical composition during the winter and early spring. Most cows are not able to consume enough low quality forage to meet their protein and possibl y energy requirements when forage quantity is lacking, especially during the winter. However, if ca ttle are able to select a diet that is greater in nutritive value than what hand-harvested sample s indicate, this may affect supplementation strategies for producers. Previous research has shown that cat tle will selectively graze when

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42 adequate forage is available for grazing (Wei r and Torrell, 1959; Fontenot and Blaser, 1965; Jung et al., 1989; Russell et al., 2004). Other resear ch has illustrated that hand-sampled forage is inaccurate in estimating forage selected by a grazing animal (Kiesling et al., 1969; Coleman and Barth, 1973; Skerman and Riveros, 1990). During the winter and spri ng months, bahiagrass forage mass can be limiting, while the forage w ill typically have greater quality since the bahiagrass is early in its growing season (Ball et al., 2002). However, due to temperature and environmental differences, the chemical compos ition and forage mass of bahiagrass will vary widely across Florida. The purpose of this study was to characterize the nutritive value of masticate or hand-sampled bahiagrass from pa stures differing in forage availability ( FA ) from four locations across the state of Florida during th e winter and spring. Materials and Methods Locations and Collections Four locations were utilized to represent variation in the Florida pasture landscape, the locations included: Range Cattl e Research and Education Center, Ona; USDASubtropical Agricultural Research Station, Brooksville; Santa Fe River Ranc h Beef Unit, Alachua; and North Florida Research and Education Center, Marianna. The soils of the research site in Ona are a sandy, siliceous, hyperthermic Alfic Alaquod (EauGallie sand). At the Brooksville research site, the soils are a loamy, siliceous, semiactive, hyp erthermic Grossarenic Paleudult (Arredondo fine sand). The soils of the research site in Alachua are a hyperthermic, uncoated Typic Quartzipsamment (Tavares sand). At the Mari anna research site, th e soils are a loamy, kaolinitic, thermic Arenic Kanha pludult (Chipola loamy sand), fi ne-loamy, kaolinitic, thermic Typic Kandiudult (Orangeburg loamy sand), a nd loamy, kaolinitic, thermic Grossarenic Kandiudult (Troup sand). The past ure sizes at each location were: 1.0 ha (Ona), 1.0 ha (Brooksville), 0.8 ha (Alachua), and 1.5 ha (Marianna). Bahiagrass ( Paspalum notatum) was the

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43 primary forage of interest for this trial. Howe ver, there were different cultivars at each location. At the Ona research site, the bahiagrass cu ltivar used for the trial was Pensacola ( Paspalum notatum cv. Suarae Parodi), while th e cultivar found in Brooksvill e was primarily Argentine bahiagrass, which is similar to Pensacola, but ma y be more palatable. At the Alachua research site, the bahiagrass cultivar was Pensacola, while Marianna contained Pensacola bahiagrass. The selected pastures were managed at each loca tion either by grazing or mowing to allow for differences in available forage mass. Pastures we re not fertilized prior to or during the trial. Samples were collected over a six-mon pe riod from December 2006 to May 2007. Eight ruminally-cannulated Angus or Brangus steers were used for this experiment (mean BW=500 kg); two steers (one Angus and one Brangus) we re placed at each location one-mon before the start of the trial. Steer fist ulation surgery and daily care were approved by the University of Florida Institutional Animal Care and Use Co mmittee (E#105). Forage and masticate samples were collected monthly (approximately every 30 days) from two pastures at each location. Forage availabilities were visually assigned to th e selected pastures, as either HIGH or LOW, at each location to represent differences in forage qu antity. Within each pa sture, two individuals hand-collected three forage samples each for a to tal of six samples per pasture. Hand shears were used to cut the forage to an appr oximate height of 3.5-cm within a 0.25-m2 quadrat. Samples were placed in paper bags, transported to the lab, and weighed. Forage samples were dried for 48 h in a 55oC forced-air oven to determine DM concentration a nd forage mass. Simultaneously, masticate samples were collect ed using two ruminally fistulated steers. At sunrise, the steers were removed from the pasture and penned for rumen evacuation; rumen contents were removed by hand as described by Lesperance et al. (1960), except that the rumen walls were also wiped with sponges to remove adhe rent particles. Both steers were allowed to

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44 graze either the HIGH or LOW designated pastur e for approximately 1 h. The masticate was removed from the rumen and excess liquid drained. Samples were stored in individual, labeled plastic cups, placed on ice for transp ort, and frozen in the lab (-200C). The masticate sample collection process was repeated for the other forage availability pasture. At the conclusion of the masticate collections, ruminal contents were returned to the steers. Laboratory Analysis Masticate samples were lyophilized to a consta nt DM content. Handcollected forage and m asticate samples were ground to pass through a 1-mm screen with a Wiley mill. All forage and masticate samples were composited by person or st eer, and pasture availab ility and subsampled. All samples were analyzed for residual DM and OM (AOAC, 2007). Concentrations of NDF and ADF were determined using an Anko m 200 Fiber Analyzer (Ankom Technology Corp., Fairport, NY) without the use of sodium sulfite or decalin (Van Soest et al., 1991). Crude protein concentration was determined by the co mbustion method using the Elementar Vario Max CN (Elementar Americas Inc., Mt. Laurel, NJ). In vitro digestible organic matter, ( IVDOM ) was determined according to Tilley and Terry (1 963), as modified by Marten and Barnes (1980), for all samples using rumen fluid inoculum obtained from a ruminally fistulated, dry Holstein cow consuming a basal diet of ad libitum berm udagrass hay and 450 g soybean meal daily. The selection index ( SI ) for chemical composition was determined using the following equation: SI={[(Masticate analyte concentration hand-co llected forage analyte concentration) / handcollected analyte forage concentration] 100} + 100. Statistical Analysis Data were analyzed as a split p lot design with the whole plot completely randomized using the MIXED procedure of SAS (SAS Inst., Inc., Cary, NC). The experimental unit was steer or person for sample collection. Fixed e ffects in the model included FA, month, sampling

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45 type (masticate or hand-collectio n), and their subsequent intera ctions. Repetition (steer or person) within each FA was used for the repeated measures and random effect. The least squares means were determined. Means were separate d using the P-diff opti on when protected by a significant F-value ( P <0.05). Results and Discussion Forage Mass Month affected the ov erall state mean forage mass (Table 3-1; P <0.001), while there was a tendency for a difference between FA ( P =0.10). All months were similar in forage mass in each respective FA, except for May, which had the gr eatest forage mass for the LOW FA, which was likely due to the onset of the summer season a nd the greater increase in forage mass at Ona compared to the other locations. The forage ma ss of HIGH FA decreased through the winter and spring until increasing to its greatest value in May. The LOW FA remained fairly constant from December to February until increasing by approx imately 500 kg/ha in March and April with a larger increase (1,500 kg/ha) in forage mass in May. Bahiagrass is reported to produce only 14% (1,800 kg/ha) of its total annual forage mass (13,000 kg/ha) during the winter (October to March; Mislevy and Everett, 1981). As noted by Williams and Hammond (1999), at the USDA-ARS Brooksville research station, bahi agrass growth and FA are affect ed by seasonality and rainfall, especially during the spring. Williams and Ha mmond (1999) reported that before mid-June, when rainfall can be limiting, FA is usually < 1,100 kg DM/ ha and low forage mass during this period can limit animal performance. The aver age forage mass (1,850 kg/ha) in this study was greater than those of Williams and Hamm ond (1999; 1,460 kg/ha); however, rainfall was limiting (Table 3-5) during both studies, thus overall forage growth during both studies was negatively affected. However, as long as bahiagrass forage mass is accumulating during the

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46 spring, as was seen in this study, cattle can select ively graze the highest quality forage material (Williams and Hammond, 1999). In Vitro Digestible Organic Matter Masticate samples were consis tently greater (Table 3-2; P <0.001) in IVDOM concentratio n by 13.3% on average compared to hand-coll ected forage samples during the winter and spring. While not as great of a difference wa s seen compared to the results of this studA smaller, but similar response in cattle grazing fe scue-lespedeza and orchar dgrass-clover pastures; selected forage material was 2.0% greater in digestible dry matter ( DDM ) compared to samples collected by hand (Coleman and Barth, 1973). Concentration of IVDOM in masticate and handcollected forage samples was also affected by month ( P <0.001). The IVDOM concentrations of the hand-collected forage samples were lowest in January, followed by December and February, while March, April, and May had the greates t values with a mean of 50.3% IVDOM (51.6% TDN; Fike et al., 2003) during the three m on. Minson and McLeod (1970) stated IVDDM concentrations less than 65% are inadequate for meeting energy requirements of cattle grazing tropical grasses. As reported by the 2000 Beef Cattle NRC, a 544 kg cow with 9 kg peak milk will require a mean of 56.3% TDN during the first three mon of lactation. Thus according to the hand-collected forage IVDOM values in Decem ber, January, and February (mean=41.3%; 47.1% TDN), grazing cattle will not be able to cons ume enough forage to meet energy maintenance energy requirements and must be supplemented to make up for the 9.2% TDN deficiency during the three mon. December, January, and February represent th e coldest months, thus limiting bahiagrass growth and maximizing senescent material, while temperature increases in March, April, and May allow for spring forage growth. Joliff et al. (1979) reported similar low IVDMD concentration (41.6%) for bermudagrass from Novemb er to February, which is likely due to the

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47 dormancy of tropical grasses during the winter. Gates et al. (2001) observed that bahiagrass pastures at two locations, Ona, FL and Tifton, GA, had variable IVDOM concentration between locations and across months. Concentration of IVDOM of hand-sampled forage decreased from September to February but increased in March and April. The sampled forage at Ona (Gates et al., 2001) was fertilized with 34 kg N/ha during the trial which ma y have resulted in greater hand-collected forage IVDOM concentration (55-65%) compared to the state mean handcollected forage IVDOM concentration from this trial (37-51%). Also, when the mean IVDOM concentrations from Ona and Tifton are averag ed from Gates et al. (2001), the mean IVDOM concentration (53.8%) is more reflective of the state mean IVDOM concentration found in this study (45.8%). The similarity of IVDOM concentration during both studies may be due to the similar temperature and environmental variation between locations of the current study, as well as the locations utilized by Gates et al. (2001). The masticate sample IVDOM concentrations were similar in December and January (mean=55.94%; 49.82% TDN), while March, Apr il, and May did not differ in IVDOM concentration with a mean of 60.28% (54.21% TDN) for the three mon. While the handcollected forage samples were unable to meet cow energy maintenance requirements during the first three mon of lactation (9.2% TDN deficiency ), values for masticate samples were also less than the recommended TDN concentration during December, January, and February. However, there was only a 1.8% deficiency in TDN concen tration during the three months for masticate samples compared to the 9.2% deficiency for hand-collected forages, thus implying producers would be able to supplement less energy during the winter than previously determined by handcollected forage TDN concentration. The sample type and month effects led to a type x month ( P <0.001) effect for IVDOM concentration during the winter. This indicates the steers were able

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48 to select forage material different in chemical composition than hand-coll ected forage material and the differences between sample types also varied during each month of the study. However, hand-collected forage and masticat e IVDOM concentrations (Table 3-3) were not affected by FA ( P =0.75 and P =0.19, respectively) during the wi nter and spring. There was a trend for a FA x month interaction for masticate IVDOM concentration ( P =0.10), but not for hand-collected forage IVDOM ( P =0.21). The lack of a FA effect is indicative of the steers selecting forage material with similar IVDOM c oncentration (59.1%) from both FA pastures. In a study by Schlegel et al. (2000) comparing esopha geal extrusa samples collected from alfalfa pastures maintained under two stocking densities (5.3 and 11.7 steers/ha); th ere was no effect of stocking density on the IVDOM and CP concentrati ons of masticate samples, suggesting steers were selecting similar forage material from both pastures. Whereas Pitman et al. (1994) reported 5% greater IVDOM concentrati on in limpograss pastures with greater stocking densities (8 steers/ha) compared to lower stocki ng densities (4 steers/ha). This contradicts the results of this study in which there were no FA or FA x month effects ( P =0.75 and P =0.21, respectively). Selection indices (SI ; Table 3-4) for IVDOM concen tration differed between FA ( P =0.04) and month ( P <0.001). The LOW FA had a 10% greater SI than the HIGH FA indicating the steers were more selective of forage material within the LOW FA comp ared to the HIGH FA. January and February did not differ in SI and ha d the greatest SI values, thus illustrating the steers ability to select forage material that was 51% greater in IVDOM concentration than the hand-collected forage values. Previous resear ch has shown (Bennett et al., 1999) that when forage mass is not limiting, the main determinant of diet selection by steers is the chemical composition of the available forage. However, in December, March, April, and May, when forage mass was similar with the excepti on of May, SI were not different (20.73, 21.29, 19.94,

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49 and 20.26%, respectively). Thus while forage gr owth was not at its full potential during the winter and spring, the steers were still able to select forage mate rial with greater digestibility than hand-clipped forage material. During th e current study, regardless of forage mass, the steers selected material that wa s greater in IVDOM compared to hand-collected forage samples. Crude Protein Sim ilar to IVDOM, CP concentrations (Table 3-2) of masticate samples were greater ( P <0.001) than those of hand-collected forage samples for the state. Masticate samples were 2.3% greater in CP concentration than the handcollected forage samples during the winter and spring, thus the steers selected a diet that was gr eater in CP concentration compared to clipped forage samples. Jung et al. (1989) found that wethers grazing smooth bromegrass selected forage material 10% greater in CP concentration compared to pasture samples. Month also affected CP concentration ( P <0.001) during the winter and spri ng, resulting in a type x month interaction ( P =0.02), which was likely influenced by the convergence of the CP data in March. For the hand-collected forage samples, CP concentration was lowest in December (7.8% CP), followed by January (9.5% CP); the remaining mon (February, March, April, and May) had relatively consistent CP concentrations, and March had the greatest hand-collected forage CP concentration of 11.9%. For a 1,200 lb beef cow ( 20 lb peak milk) in the first three mon of lactation, the NRC (2000) recomm ends intake of 10.2% CP to meet maintenance requirements for protein. Based on the hand-collected forage samples, bahiagrass in December and January will have 1.5% less CP than required total dietary CP for lactating beef cattle. However, for the remainder of the spring, bahiagrass pastures had 1.2% excess CP concentration than required for lactating beef cattle, thus protein supplementa tion is not needed (NRC, 2000). Gates et al. (2001) reported that CP concentrations of bahi agrass remained relatively constant from autumn until early spring ranging from 13-17% CP. While Gates reported bahiagrass with greater CP

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50 concentrations compared to th e current study (7-12% CP), the forage was fertilized with 34 kg N/ha thus contributing to greater CP concentration; Johnson et al. (2001) reported that bahiagrass total N concentration increased wi th increased N fertilization. Re gardless, our data demonstrate a similar pattern to Gates et al (2001) since hand-collected forage CP concentration remained fairly constant during the wint er and spring period except in December and January when CP concentrations were lowest. Masticate CP concentrations were the least in December, January, and March (mean=11.5% CP); the greatest masticate CP concen trations occurred in February, April, and May (mean=13.2% CP). The CP concentration of masticate samples were in excess of recommended CP requirements for lactating beef cattle (NRC, 2000) during the entire sampling period; indicating bahiagrass pa stures provide adequate CP concentration when steers are selectively grazing. Dubbs et al. (2003) reported th at tall fescue CP concentrations were greatest in April until they decreased in May with masticate samples having approximately 6% greater CP concentration than hand-collec ted forage samples. Since tall fescue is a cool-season grass, the nutritive value will begin to decrease at the end of the spring, as seen by the results of Dubbs et al. (2003), whereas bahiagrass, a warm-season grass, will have greatest CP concentration at the same time, as indicated by the current study. Waterman et al. (2007) reported that the CP concentration of ruminal extrusa from cows grazing range grasses found in the Great Plains [grama ( Bouteloua gracilis ), needlegrass ( Stipa pennata ), and wheatgrass ( Tritcum aestivum )] followed typical seasonal patterns with lowest CP concentrations in winter (7.9% CP; December) and greatest concentrations in early summer (12.1% CP; May) with substantial increases in early spring (8.1% CP; March) due to the onset of th e primary growing season. There was a trend (Table 3-3; P =0.08) for greater CP on the HIGH FA past ures. While the HIGH FA had greater

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51 forage mass, the forage mass was less mature ; whereas the LOW FA may have had more senescent forage material and not enough new grow th to strongly impact CP concentration. The type and month effects led to a type x month interaction ( P =0.02) for CP concentration indicating the differences between masticate and hand-collected fo rage samples and the variation between months during the study. The SI (Table 3-4) for CP concentration was affected by FA ( P =0.01) and month ( P =0.03). The SI for the LOW FA was nearly 20% greater than the HIGH FA. There was greater forage mass in the HIGH FA, but greater selectivity in the LOW FA, which may have contained greater amounts of senesced material. The data indicates th e steers were selective of forage material that was greater in CP concentration although there may have been a prevalence of dead forage material. This data contrasts with the results of Jung et al. (1989), who reported that SI for CP concentration (115%) did not differ between br omegrass pastures with different stocking densities (15 vs 30 lambs/ha). The contrast ma y have been due to the differences in forage species between the two studies. There was litt le indication of selec tion for CP during March (0.16%) with moderate selection during April (16.42%) and May (12.76%), while the greatest selection (mean=33%) occurred in December, January, and February. These results demonstrate that cows requiring 10.2% CP during the first three mon of lactation could select bahiagrass forage with adequate CP concentration to meet maintenance requirements for CP. In a range grass grazing study, Bailey (1995) demonstrated that steers devel op preferences for forage with greater CP concentrations regard less of the forage quantity availa ble, which contrasts the results of this study. Weir and Torrell (1959) reported that esophageal extrusa samples had greater CP concentration than those of hand-clipped forage, as seen in this study.

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52 Neutral Detergent Fiber There was an effect (Table 3-2) of sam pling type and month ( P <0.001) on NDF concentrations with a slight trend (P =0.13) for a type x month effect. Forage samples had greater NDF concentration across all months compared to masticate samples (mean difference=5.2%). Neutral detergen t fiber concentrations of handcollected forage samples were lowest in March (55%), followed by April (57%) and May (59%), and grea test in December and January (mean=63%). These results are because bahiagrass would be regrowing during the early spring, and thus will have low NDF concentrations due to the relatively lower concentration of cell wall constituents in young, immature plants (Barnes et al., 2007). However, shorter day length and cold temperatures in December and January may have increased senescence of bahiagrass forage and therefore increased its NDF concentration. Waterman et al. (2007) observed that NDF concentration of range gras ses during a two-yr st udy increased during the production season (May to December). The gr eatest concentration of NDF occurred in December, mainly because of the presence of senescent material, while the lowest NDF concentration was in May due to th e immaturity of the forages. In the current study, masticate NDF concentr ation was lowest in February and March (49%), followed by April and May (53%), and gr eatest in December and January (60%). During the winter, hand-collected forages will have incr eased amounts of senescent material, thus fiber concentrations will be greater. However, in the spring, cell wall components of bahiagrass will be less due to the immaturity of the forage. The hand-collected forage samples averaged 5.3% greater NDF concentration during the trial compared to masticate samples, which is similar to differences reported by Dubbs et al. (2003). The results imply th at cows are able to select material that is lower in ce ll wall components compared to fo rage samples collected by handclipping during the spring. There were no differences in NDF concentration between FA for

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53 hand-collected forage ( P =0.72) or masticate samples (P =0.18). The data indicates handcollected forage NDF concentration did not di ffer between FA and the selection of forage material by steers was similar in NDF con centration between both FA. However, NDF concentration of masticate samples was less th an hand-collected forage NDF concentration during the winter and spring. There was a trend (Table 3-4; P =0.10) for a month effect on SI of NDF concentration. The lower SI for NDF concentration indicates that the steers selected a di et lower in cell wall components compared to hand-collected forage samp les. However, there were no differences in the SI ( P =0.16) for NDF concentration between HI GH and LOW FA for both hand-clipped and masticate samples. In the trial by Dubbs et al (2003), hand-clipped tall fescue samples had 5% greater NDF concentration compared to masti cate samples during April and May. Fescue is dormant during April and May, steers were select ing forage material with the lowest proportion of cell wall contents even though the forage itself was low in fiber content. Bahiagrass has been classified as extremely fibrous when mature (Chambliss and Sollenberger, 1991). However, research has found that cattle are less selective of NDF compared to other ruminant species (Reid et al., 1990) because of their ability to maintain high levels of intake of cell wall constituents. This selective ability proves to be useful wh en dealing with Florida s subtropical grasses, especially during the winter when forages may not be as mature as during the summer months, while still having considerable NDF concentration due to their C4 anatomy. Acid Detergent Fiber Sa mpling type (Table 3-2) affected ADF c oncentration of hand-collected forage and masticate samples ( P <0.001). Masticate samples concentrations of ADF were less than handcollected forage sample concentrations (mean difference=3.5%). The exception was in April when hand-collected forage and masticate ADF concentration only differed by 0.5%, resulting in

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54 a type x month effect (P <0.001). Dubbs et al. (2003) reported differences in ADF concentration between masticate and hand-clipped samples of fescue pastures across sampling months with hand-clipped samples 5% greater in ADF concentration during the study. There was a trend for a month effect ( P =0.10) on ADF concentration. Acid detergent fiber co ncentrations are lowest in young, immature forage and will increase with increasing maturity as winter and spring progress to the summer season (Barnes et al ., 2007). Hand-collected forage sample ADF concentration was greatest in February (37%) while the remaining months had a mean ADF concentration of 31%, suggesting a prevalence of senescent material in February. In contrast, Davis et al. (1987) reported no change in ADF concentration of limpograss from December to April, which may have been due to the lack of growth during the winter, since limpograss is a warm-season perennial grass. While bahiagrass is also a warm-season perennial grass, the differences between the results of this study and those of Davis et al. (1987) may have been influenced by the anatomical differences of the forages such as leam:stem ratios. Masticate ADF concentrations were lowest in February, March, and May (mean=26.6%), whereas December, January, and April had the greatest concentrations of ADF (mean =30.5%). These results indicate that although there was an abundanc e of dead forage material in the pastures during the winter months, as demonstrated by the hand-clipped forage samples, the steers were still able to select forage material that was lower in ADF concentr ation compared to clipped forage samples during the winter and spring. Similarly, in a study co mparing hand-clipped tall fescue samples to masticate samples, Dubbs et al. (2003) conclu ded that hand-clipped samples had greater ADF concentrations ( P <0.01) compared to masticate sa mples during April and May. The SI for ADF concentration was affected by month ( P =0.001). There was also a trend for a difference in SI between FA for ADF concentration ( P =0.07). The steers selected forage

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55 material that was lowest in ADF concentrati on during February and March with the remaining months not differing from each othe r and eliciting less of a select ion response. Norman et al. (2004) concluded sheep that grazing saltbushes will not show preference for forage material based on ADF concentration. The negative SI values for February and March indicate that steers selected forage that was lower in ADF concentration. Implications Results of this study indicate that steers gr azing bahiagrass forage during the winter and spring selected forage with gr ea ter digestibility and CP concentration compared to handcollected forage samples. These results imply that cow-calf producers need to properly evaluate the nutritive value of their pastur es in order to correctly supplemen t their herd during the winter.

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56 Table 3-1. Effect of forage availability a nd month on overall mean forage mass (kg/ha). Month P -value FAa Dec Jan Feb Mar Apr May SEM d FAMonth FA*Month H b 2,808 2,050 2,140 1,215 9962,276464 0.100.001 0.73 Lc 1,298 936 1,050 1,541 1,4743,023 aFA= Forage availability. bH = High forage availability. cL= Low forage availability. dSEM= Standard error of mean, n=192. Table 3-2. Effect of sampling type and m onth on chemical composition of bahiagrass. Month P -value Analysis Typea Dec Jan Feb Mar Apr May SEMe Type Month Type*Month IVDOM b Fc 44.2 37.5 42.249.650.850.51.98 <0.001 <0.001 <0.001 M d 55.6 56.3 62.660.659.860.5 CP F 7.8 9.5 10.811.911.711.30.58 <0.001 <0.001 0.02 M 10.6 11.9 13.411.913.612.5 NDF F 62.9 62.2 59.954.557.558.71.77 <0.001 <0.001 0.13 M 59.0 60.7 49.748.752.653.7 ADF F 31.1 31.8 37.433.329.528.71.39 <0.001 0.10 <0.001 M 30.1 31.5 25.827.429.926.6 DM F 91.2 91.3 90.790.790.590.70.29 <0.001 0.01 <0.001 M 91.0 91.1 90.991.991.693.1 OM F 94.7 94.3 94.693.893.894.31.17 <0.001 0.02 0.03 M 83.9 83.3 87.886.786.690.1 aType= Forage sampling type. bIVDOM= In vitro digestible organic matter. cF= Hand-sampled forage. dM= Masticate. eSEM= Standard error of the mean, n=192.

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57 Table 3-3. Effect of forage availability on chemical analysis of bahiagrass. FAa Analysis H b Lc SEM d P -value Forage IVDOMe 46.2 45.4 1.54 0.75 CP 11.3 9.6 0.45 0.08 NDF 59.1 59.5 0.66 0.72 ADF 32.0 31.9 0.55 0.91 DM 91.0 90.7 0.13 0.24 OM 94.0 94.4 0.14 0.24 Masticate IVDOM 57.9 60.4 0.95 0.19 CP 12.3 12.3 0.33 0.99 NDF 52.8 55.6 1.00 0.18 ADF 27.9 29.2 0.80 0.35 DM 91.8 91.5 0.23 0.49 OM 85.3 87.6 0.08 0.19 aFA= Forage availability. bH= High forage availability. cL= Low forage availability. dSEM= Standard error of the mean, n=48. eIVDOM= In vitro digestible organic matter.

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58 Table 3-4. Effect of forage availabili ty and month on steer selection indexa of bahiagrass forage. FA b Month Analysis Hc L d SEMe P -value Dec Jan Feb Mar Apr May SEMeP -value IVDOM f 125.78 135.9 3.40 0.04 120.7 i 151.8g h 151.1g121.2 i 119.9 i 120.3 i 5.73 <0.001 CP 112.2 131.5 5.10 0.01 136.5 h 131.0 h 130.1 h 100.2g 116.4g h 112.8g h 8.59 0.03 NDF 88.8 93.1 2.11 0.16 93.6 98.282.589.0 91.191.2 3.56 0.10 ADF 85.6 95.3 3.65 0.07 98.8 h 101.7 h 66.1g 80.7g 101.9 h 93.7g h 6.17 0.001 a{[(Masticate concentration forage concentr ation) / forage concentration] 100} + 100. bFA= Forage availability. cH= High forage availability. dL= Low forage availability. eSEM= Standard error of the mean, n=48. fIVDOM= In vitro diges tible organic matter. g,h,iWithin a row, means with a different superscript differ, P <0.05.

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59 Table 3-5. Precipitation data (c m) Winter 2006 and spring 2007. Month Location Nov Dec Jan Feb Mar Apr May Ona 30-yr average 1.7 5.3 7.0 4.5 3.7 5.4 5.1 6.2 1.6 7.9 4.2 4.7 1.0 9.8 Brooksville 30-yr average 5.1 6.1 6.3 6.2 3.2 8.3 7.0 8.2 2.9 10.7 4.9 6.7 3.0 8.6 Santa Fe 1.9 8.7 8.94.53.92.76.4 30-yr average Marianna 30-yr average 5.8 8.7 10.5 7.0 13.9 9.8 11.1 15.4 15.5 9.4 6.3 12.2 11.0 2.8 15.5 8.3 2.6 9.8 9.2 5.7 10.7 Table 3-6. Temperature data (0C) Winter 2006 and spring 2007. Month Location Dec Jan Feb Mar Apr May Ona 30-yr average 19.1 17.0 17.1 15.9 15.3 16.5 19.0 18.8 20.1 21.1 23.1 24.4 Brooksville 30-yr average 17.4 16.3 15.6 15.4 13.9 16.3 18.0 19.1 19.2 21.4 22.9 24.6 Santa Fe 14.8 12.9 12.016.317.821.5 30-yr average Marianna 30-yr average 13.4 12.6 10.8 14.1 11.2 9.6 12.6 10.5 11.4 17.2 17.0 15.2 19.9 18.0 18.5 23.6 23.7 22.7

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60 CHAPTER 4 EFFECTS OF FORAGE SAMPLING METHOD ON NUTRITIVE VALUE OF B AHIAGRASS DURING THE SUMMER AND FALL Introduction Florida p astures are comprised primarily of tropical and subtropical forages, which are typically low in quality, yet wi ll yield high quantities of DM (Skerman and Riveros, 1990). Bahiagrass ( Paspalum notatum ) occupies approximately one million hectares within Florida and is the primary component of diets of grazing cattle in Florida (Chamb liss and Sollenberger, 1991). Bahiagrass has a primary s easonal production from April to October (Ball et al., 2002). Advantages to providing bahiagrass in a cattle grazing system are persis tence under little to no management, and moderate quality during most of the year. However, a consistently high-quality bahiagrass is rarely achieved, re gardless of management or fertilization and may not be a good forage choice for cattle with grea ter nutritional requirements, such as lactating or pregnant cattle (Pate, July 1992). As with many tropical grasse s, bahiagrass has been re ported to be low in nutritive value, especially during the summer a nd fall months, as determined by hand-harvested samples (Brown and Mislevy, 1988); however, this da ta does not account for the ability of cattle to selectively graze within a pasture. According to the NRC (2000), bahiagrass contains no more than 8.9% CP and 54.0% TDN on a DM-basis. However, if cattle are able to sel ect a diet that is greater in nutritive value than hand-harvested forage samples, supplementati on strategies for producers may be affected. Previous research has shown an inverse relationship between ma turity and quality of grasses during the summer months (Connor et al., 1963), while other studies have shown that when adequate forage is available for grazing, rumi nants will selectively graze (Weir and Torrell, 1959; Fontenot and Blaser, 1965; Jung et al., 1989; Russell et al., 2004). Other research has illustrated that hand-sampled forage is inaccurate in its estimation of a grazing animals selected

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61 diet (Kiesling et al., 1969; Co leman and Barth, 1973; Skerman and Riveros, 1990). During the summer and fall, bahiagrass forage is in its gr eatest production phase; ho wever, forage quality declines significantly as the growing seas on progresses. Also, due to temperature and environmental differences, the chemical compos ition and forage mass of bahiagrass varies widely across Florida. The purpose of this study was to characterize the chemical composition of bahiagrass from four locations across th e state of Florida duri ng the summer and fall by comparing sampling techniques, either by handsampling or collection of masticate sample, within pastures of varying levels of forage availability ( FA ). Materials and Methods Locations and Collections Four locations were utilized to represent variation in the Florida pasture landscape, the locations included: Range Cattl e Research and Education Center, Ona; USDASubtropical Agricultural Research Station, Brooksville; Santa Fe River Ranc h Beef Unit, Alachua; and North Florida Research and Education Center, Marianna. The soils of the research site in Ona are a sandy, siliceous, hyperthermic Alfic Alaquod (EauGallie sand). At the Brooksville research site, the soils are a loamy, siliceous, semiactive, hyp erthermic Grossarenic Paleudult (Arredondo fine sand). The soils of the research site in Alachua are a hyperthermic, uncoated Typic Quartzipsamment (Tavares sand). At the Mari anna research site, th e soils are a loamy, kaolinitic, thermic Arenic Kanha pludult (Chipola loamy sand), fi ne-loamy, kaolinitic, thermic Typic Kandiudult (Orangeburg loamy sand), a nd loamy, kaolinitic, thermic Grossarenic Kandiudult (Troup sand). The past ure sizes at each location were: 1.0 ha (Ona), 1.0 ha (Brooksville), 0.8 ha (Alachua), and 1.5 ha (Marianna). Bahiagrass ( Paspalum notatum) was the primary forage of interest for this trial. However, there were different cultivars at each location. At the Ona research site, the bahiagrass cu ltivar used for the trial was Pensacola ( Paspalum

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62 notatum cv. Suarae Parodi), while th e cultivar found in Brooksvill e was primarily Argentine bahiagrass, which is similar to Pensacola, but ma y be more palatable. At the Alachua research site, the bahiagrass cultivar was Pensacola, while Marianna contained Pensacola bahiagrass. The selected pastures were managed at each loca tion either by grazing or mowing to allow for differences in available forage mass. Pastures we re not fertilized prior to or during the trial. Samples were collected over a six-mon pe riod from June to November 2007. Eight ruminally-cannulated Angus or Brangus steers were used for this experiment (mean BW=500 kg); two steers (one Angus and one Brangus) we re placed at each location one-mon before the start of the trial. Steer fist ulation surgery and daily care were approved by the University of Florida Institutional Animal Care and Use Co mmittee (E#105). Forage and masticate samples were collected monthly (approximately every 30 days) from two pastures at each location. Forage availabilities were visually assigned to th e selected pastures, as either HIGH or LOW, at each location to represent differences in forage qu antity. Within each pa sture, two individuals hand-collected three forage samples each for a to tal of six samples per pasture. Hand shears were used to cut the forage to an appr oximate height of 3.5-cm within a 0.25-m2 quadrat. Samples were placed in paper bags, transported to the lab, and weighed. Forage samples were dried for 48 h in a 55oC forced-air oven to determine DM concentration and forage mass. Simultaneously, masticate samples were collected using two ruminally fist ulated steers. At sunrise, the steers were removed from the pa sture and penned for rumen evacuation; rumen contents were removed by hand as described by Lesperance et al. (1960), except that the rumen walls were also wiped with sponges to remove adhe rent particles. Both steers were allowed to graze either the HIGH or LOW designated pastur e for approximately one h. The masticate was removed from the rumen and excess liquid drained. Samples were stored in individual, labeled

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63 plastic cups, placed on ice for transp ort, and frozen in the lab (-200C). The masticate sample collection process was repeated for the other forage availability pasture. At the conclusion of the masticate collections, ruminal contents were returned to the steers. Laboratory Analysis Masticate samples were lyophilized to a consta nt DM content. Handcollected forage and m asticate samples were ground to pass through a 1-mm screen with a Wiley mill. Each individually collected sample, forage or masticate, was compos ited by person or steer, a nd pasture availability and subsampled. All samples were analyzed for DM and OM (AOAC, 2007). Concentrations of NDF and ADF were determined using an Ankom 200 Fiber Analyzer (Ankom Technology Corp., Fairport, NY) without the use of sodium sulf ite or decalin (Van Soest et al., 1991). Crude protein concentration was determined by the co mbustion method using the Elementar Vario Max CN (Elementar Americas Inc., Mt. Laurel, NJ). In vitro digestible organic matter, ( IVDOM ) was determined according to Tilley and Terry (1 963), as modified by Marten and Barnes (1980), for all samples using rumen fluid inoculum obtained from a ruminally fistulated dry Holstein cow consuming a basal, daily diet of ad libitum bermudagrass hay ( Cynodon dactylon ) and 450 g of soybean meal. The selection index ( SI ) for chemical composition was determined using the following equation: SI= {[(Masticate concentrati on hand-collected forage concentration) / hand-collected forage concentration] 100} + 100. Statistical Analysis Data were analyzed as a split p lot design with the whole plot completely randomized using the MIXED procedure of SAS (SAS Inst., Inc., Ca ry, NC). The experimental unit was steer or person for sample collection. Fixed effects in the model included FA, month, sampling type (masticate or hand-collection), and their interacti ons. Repetition (steer or person) within each

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64 FA was used for the repeated measures and random effect. The least squares means were determined. Means were separated using the P-diff option when prot ected by a significant Fvalue (P<0.05). Results and Discussion Forage Mass Forage m ass (Table 4-1) was affected by month ( P <0.001) and FA ( P =0.03), while there was a tendency for a FA x month effect ( P =0.06). Overall, September had the greatest forage mass (8,474 kg/ha), followed by August, Octobe r, and November (mean=7,024 kg/ha), while July forage mass (4,077 kg/ha) was only greater th an the lowest forage mass, which occurred in June (2,100 kg/ha). Both HIGH and LOW FA increas ed in forage mass from June to September, when yields began to decline. Forage mass of the HIGH FA increased from a minimum in June (2,567 kg/ha) to a maximum in September ( 12,032 kg/ha) and declined to 9,292 kg/ha in November. Forage mass of the LOW FA increased by approximately 5,000 kg/ha from June to a maximum value of 5,401 kg/ha in October thereafter a moderate decrease occurred in November (3,333 kg/ha). During the months with the great est forage mass (August, September, October, and November), the LOW FA had a mean of approximately 5,000 kg/ha, while the HIGH FA averaged 11,000 kg/ha during the months with the greatest forage mass (September and October). Similar to the results of this st udy, Brown and Mislevy (1988) noted that tropical grasses had greater forage mass during the summer compared to spring growth, with a decrease in IVDOM and CP concentration, and increase in NDF and ADF concentration as maturity increased. In a study by Bertrand and Dunavin (1985) comparing bahiagrass in North Florida over three consecutive summer and fall seasons mean forage mass was 8,824 kg/ha, which is greater than our seasonal mean fora ge mass of nearly 6,000 kg/ha.

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65 The FA x month trend was likely influenced by the simultaneous gains and losses of forage mass for the HIGH and LOW FA duri ng the trial. Seasonal growth patterns for bahiagrass have been shown to decline in late summer and fall due to declining temperature and decreasing day length (Gates et al., 1999). Prev ious research conducted by Willia ms et al. (1994) observed that bahiagrass forage mass increased from June to an approximate maximum forage mass in August or September, depending on the stocking density and cultivar being utilized, while forage mass decreased through November. The results of Willia ms et al. (1994) correspond to the results of this study, with increased forage mass from June to September and decreased forage mass from September to November. Bahiagrass growth and forage availability is affected by seasonality and rainfall, which can limit animal performance when adequate forage is not available for meeting nutritional requirements (Williams and Hammond, 1999). However, as long as bahiagrass forage mass is accumulating, cattle can selectively graze for the highest quality forage material (Williams and Hammond, 1999). In Vitro Digestible Organic Matter Masticate samples were consis tently greater (Table 4-2; P <0.001) in IVDOM concentration com pared to hand-collected forage samples, averaging 9% greater IVDOM during the summer and fall. In a study conducted by Fi sher et al. (1991), st eers grazing either flaccidgrass (Pennisetum flaccidum) switchgrass (Panicum virgatum) bermudagrass, or tall fescue ( Festuca arundinacea) pastures during the summer and fall selected forage material consistently greater in IVDMD concentrati on (mean difference=16.9%) compared to the handharvested forage samples. Cattle grazing fescue-lespedeza ( Festuca arundinacea-Lespedeza stipulacea ) and orchardgrass-ladino clover ( Dactylis glomerata-Trifolium repens ) pastures selected forage material greater in digestib le dry matter (mean=64.3%) compared to samples collected by hand ( DDM ; mean=62.2%) from May to November (Coleman and Barth, 1973).

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66 Concentration of IVDOM of hand-collected forage samples was affected by month (P <0.001). The IVDOM concentration of the hand-collected forage samples was lowest in August and November, while October had the greatest IVDOM concentration with a mean of 55.0% (55.6% TDN; Fike et al., 2003). As reported by the B eef Cattle NRC (2000), a 1,200 lb cow with 20 lb peak milk production requires a mean TDN con centration of 49.2% from five to 11 mon after calving, corresponding to the summer and fall months This indicates that the hand-collected forage samples have greater TDN than the beef cattle require, thus supplementation of energy is not required. Previous research by Williams et al. (1994) indicat ed rotationally-grazed bahiagrass pastures increased in forage IVDOM concentration from June to either August or September, depending on the grazing system utilized, before decreasing in IVDOM concentration from September to November. In the current study, as forage mass increased from June to September, hand-collected forage diges tibility decreased and forage maturity increased; however, IVDOM concentration increased again in September and October until reaching its minimum in November likely because of the infl uence of colder temperatures and shorter day length, which have negative effects on nutritiv e value of warm-season grasses (Barnes et al., 2007). Masticate sample IVDOM concentra tion was also affected by month ( P <0.001). The masticate IVDOM concentration was similar in June and November with a mean IVDOM concentration of 57% (54.2% TDN), while during the remaining months masticate samples had greater IVDOM concentration (mean=62%; 57.8% TDN). The sample type and month effects led to a type x month ( P =0.08) trend for IVDOM concentration during the summer and fall. Masticate and hand-collected forage samples had adequate TDN to meet nutritional requirements of grazing cattle. In a study by Johnson et al. (1998), mixed-grass prairi e decreased in IVDOM

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67 from June to November indicating that as the season progressed, forage quality as determined by IVDOM declined. Masticate IVDOM concentration (Table 4-3) was not affected by FA ( P =0.39) during the summer and fall, while FA only tended ( P =0.09) to have an effect on hand-collected forage IVDOM concentration. However, there was a FA x month effect for masticate and handcollected forage IVDOM concentration ( P <0.001 and P =0.04, respectively) indicating the forage selected by hand and by the steers was different between the HIGH and LOW FA, as well as between months. Anderson et al. (1988), compared the digestibility of different strains of switchgrass and concluded that although increase d FA can enhance selective grazing, the overall nutritive value of the forage may have a negative influence on selection of forage material, particularly if the forage is low in IVDMD. Thus steers grazing switchgrass with HIGH (4,972 kg/ha) and LOW FA (2,990 kg/ha) may select forage material with greater IVDMD concentrations (Anderson et al., 1988). This is si milar to the results of the current study in which masticate IVDOM concentration was not affected by FA as maturity of the forage increased. Selection indices (Table 4-4) did not differ between FA ( P =0.48) or month ( P =0.43) for IVDOM concentration. During this study, regardle ss of forage mass, steers selected forage material that was about 19% greater in IVDOM concentration on average compared to handcollected forage samples. Jung et al. (1989) re ported that masticate IVDMD from lambs grazing bromegrass (Bromus inermis) were 12% greater than hand-sampled forage IVDMD concentrations taken from May to August during a th ree-yr trial. Similar to the results of this study, Fisher et al. (1991) demonstrated that steers grazing bermuda grass, switchgrass, flaccidgrass, or tall fescue from May to Sept ember selected forage that had 16.9% greater IVDMD compared to hand-collected forage sample s. The lack of a difference in SI among FA

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68 and month indicates that month or FA did not a ffect forage selection. Thus selection did not change during the summer and fall seasons. Al though selection of forage material occurred, hand-collected forage IVDOM concentrations we re adequate to meet TDN requirements of lactating cows during the summer and fall, thus an energy supp lementation program would not be needed. Crude Protein Month affected CP concentrati on of hand-collected forage an d m asticate samples (Table 42; P <0.001) during the summer a nd fall, resulting in a t ype x month interaction ( P <0.001). The type x month interaction was likely influenced by the intersection of th e hand-collected forage and masticate CP values in June and the lower reductions in CP concentrations of masticate versus hand-collected forage samples as the seas on progressed. The lack of rainfall in May and June may have influenced forage mass, as we ll as hand-collected forage chemical composition variation between months. At most locations, pr ecipitation was less than the 30-yr average for all locations from May to November (Table 4-5). Forage CP concentration was greatest in June (13.93%), whereas November had the lowest hand-c ollected forage CP concentration (8.29%). According to the 2000 Beef Cattle NRC (2000), a 1,200 lb cow with 20 lb peak milk production requires a mean CP concentration of 7.02% five to11 mon post-calving, which corresponds to the summer and fall season. The results from this st udy indicate that hand-collected forage CP values were in excess of cow requirements (NRC, 2000), thus protein supplementation would not be needed during the summer and fall. Johnson et al. (1998) reported that steers grazing range grasses in the Northern Great Plai ns selected forage that decreases in CP concentration from June (13.6%) to December (6.2%). The results of Johns on et al. (1998) are similar to those of this study in which CP concentration of hand-collecte d forage and masticate samples decreased as the season progressed and forage maturity increased. Williams et al. (1994) concluded that CP

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69 concentration of continuously and rotationally stocked bahiagra ss pastures decreased linearly from May to November. Chambliss and Sollenberger (1991) reported that as weeks of regrowth between bahiagrass cuttings increase during the summer and fall, CP concentration decreases by nearly 7% CP from June to August, which is similar to the almost 6% decrease in hand-collected forage CP during this trial. Arthington and Br own (2005) reported that w ith increasing maturity (4vs. 10-wk regrowth) of tropica l grasses, a 38% decrease in CP concentration can be expected. In the current study, FA did not affect CP concen tration (Table 4-3) of either hand-collected forage or masticate samples (P =0.24 and P =0.17, respectively). The similarities in CP concentration between FA for hand-collected fora ge and masticate samples may have been due to greater forage mass seen in the summer and fall. Thus th e forage mass was great enough to provide similar CP concentration within both FA as selected by person or steer. Similar to IVDOM, CP concentration (Table 42) of masticate sample s were consistently greater ( P <0.001) than those of the handcollected forage samples except in June. Masticate samples averaged 1.4% greater CP concentration than the hand-collected forage samples during the summer and fall, thus the steers selected a diet that was slightly greater in CP concentration compared to hand-clipped forage samples. Dubbs et al. (2003) reported that CP concentrations of tall fescue samples were approximately 4.5 % greater than hand-coll ected forage samples from April to September. Also, Jung et al. (1989) found that wethers grazing smooth bromegrass selected forage material that was 10% greater in CP concentration compared to pasture samples. Masticate CP concentrations we re greatest in June and July with a mean of 12.5%, while the other months had similar, lower CP concentratio n (mean=10.3%). These data are similar to the summer results of Connor et al. (1963), who re ported declining CP c oncentration of steer masticate samples of Nevada range grass from May (12.9%) to August (11.0%) with a slight

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70 increase in concentration in September (11.7%) fo llowed by a decrease in October (9.7%). In a study conducted by Waterman et al. (2007) using ru minally fistulated cows grazing range grasses in the Northern Great Plains, CP concentration of extrusa samples were greatest in May (12.1%) and decreased through August (7.6%), which is sim ilar to the results of this study. Bailey (1995) concluded that in heterogeneous areas of forage cattle will develop preferences for patches of grass with greater CP concentration regardless of forage quantity. The SI (Table 4-4) for CP concentrat ion was not affected by FA or month ( P =0.72 and P =0.89, respectively). The SI for the HIGH and LOW FA indicated that the steers were able to select forage that was 20% grea ter in CP compared to hand-colle cted forage samples. While there were no differences between month (P =0.16) in SI for CP c oncentration, there was no selection in June (-3%), while the other summer and fall months had a mean SI of 25%. As in this study, Weir and Torrell (1959 ) reported that esophageal extrus a samples of native range, as well as temperate grasses and legumes were gr eater in CP concentration (mean=18.0%) than forage samples collected by hand-clipping (mean =14.7%). According to a study conducted by Bennett et al. (1999), when forage mass is not lim iting, the principle factor driving selection is the chemical composition of the available forage During the current trial, while forage mass was abundant and while hand-collected forage CP concentration decreased to a minimum of 8.3%, the steers were still able to select fora ge material 25% greater in CP concentration compared to hand-clipped samples. However, th e CP concentrations of hand-collected forage and masticate samples were greater than the CP requirement for a lactating cow (NRC, 2000; 7.02% CP), thus supplementation would not be necessary during the summer and fall seasons. Neutral Detergent Fiber There was an effect of sam pling type (Table 4-2; P <0.001) and month ( P =0.04), thus resulting in a type x month interaction ( P <0.001) for NDF concentration. Forage samples had

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71 greater NDF concentration across all months except June and July for NDF (mean=62%) compared to masticate samples (mean=58%). Th e NDF concentrations of hand-collected forage and masticate samples in June and July may have been influenced by the lack of rainfall, thus slowing growth and subsequent in crease in fiber as seen during the summer. The similarity in hand-collected forage NDF concentration betwee n August, September, October and November, which is the primary growing seas on for bahiagrass, would be attr ibuted to the greater deposition of cell wall constituents as the forage matured (Barnes et al., 2007) Similar to the results of Brown and Mislevy (1988) repor ted consistent NDF concentra tion from June to September (mean=80.4%). Research has shown the influence of month and stage of maturity, especially during the summer and fall, on NDF concentration. Karn et al. (2006) examined the chemical composition of four perennial grasses, bromegrass and three species of wheatgrass ( Tritcum aestivum ) and concluded that while the rate of ND F accumulation within plant tissues differed between the species, the concentration of NDF increased by 10% in all forages as maturity advanced. Previous research by Wilson and t Mannetje (1978) repor ted that the cell wall content of buffelgrass ( Pennisetum ciliare ) and green panic ( Panicum maximum) in Australia was lowest in spring, and greatest in summer a nd autumn. Cuomo et al. (1996) reported that bahiagrass increased in NDF concentration durin g midto late-summer (mean=66.0%) compared to early summer harvests (63.1%). Masticate NDF concentration was greatest ( P <0.001) in June (61%) and remained relatively constant until October, and then decreased considerably in November (51%). During the summer and early fall, cell wall concentrations of bahiag rass are greatest due to the advancing maturity of the forage, which is also reflected in the masticate samples. The handcollected forage samples had a mean NDF concentration that was 3.5% greater ( P <0.001) during

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72 the trial compared to masticate samples implying the steers were able to select forage material with lower NDF concentration compared to ha nd-clipped forage samples. There are also indications that even as forage mass decreased in November as compared to the mid-summer months, the steers were still consuming forage w ith decreased NDF concentrations compared to hand-clipped samples. There were also no di fferences between NDF concentrations of HIGH and LOW FA for hand-collected forage or masticates samples ( P =0.37 and P =0.93, respectively). This may have been due to the increased forage mass during the summer and fall thus the opportunity for se lection of NDF concentrati on was similar between FA. There was a month effect (Table 4-4; P =0.001) on SI for NDF concentration. However there were no differences ( P =0.16) in SI between HIGH and LOW FA indicating the steers were selecting forage material similar in NDF concentration at both FA. The greatest SI was observed in July (12%), however there was little indicatio n of a selection response from August to October (mean=-7%) and the lowest SI occurred in N ovember (-19%). The low SI in November indicates that when forage mass was abundant the steers selected forage material with nearly 20% less NDF concentration compared to hand-colle cted forage samples, while the other months elicited less of a select ion response. Therefore, although pl ant physiological processes resulted in increasing NDF concentration with matur ity, steers selected fo rage with less NDF concentration. Bahiagrass has been classified as extremely fibrous and low in feeding value when mature (Chambliss and Sollenberger, 1991). However, cattle are less selective of NDF concentration (Reid et al., 1990) beca use of their ability to maintain greater levels of intake of cell wall constituents compared to other ruminant species, which may explain the variability of the SI between months. The results indicate that steers are less selectiv e of NDF concentration during the summer and fall when forage mass is greatest, there was still selection for IVDOM

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73 and CP concentration. Thus steers may be able to meet energy and protein requirements even while bahiagrass has greater NDF concentration by selecting forage with lower NDF concentration. Acid Detergent Fiber Acid detergent fiber concentration of hand-co llected forage and masticate samples (Table 4-2) was affected by sa mpling type and month ( P =0.002 and P <0.001, respectively) resulting in a type x month interaction ( P <0.001). There were no differences between hand-collected forage ADF concentration between HIGH and LOW FA ( P =0.83). Overall, masticate samples were 1.5% lower in ADF concentration than hand-co llected forage samples during the summer and fall. The exceptions were the lower ADF con centrations of hand-collected forage versus masticate samples in June (1.3%) an d August (0.02%). As in the Ju ly and October data from this study, Dubbs et al. (2003) reported that hand-cl ipped samples of fescue pastures were 3.0% greater in ADF concentration from April to Sept ember. Forage sample ADF concentration was lowest in June (29%) and increased to 33% in October and November. Acid detergent fiber concentrations are generally le ss in young, immature forage and would increase with increasing maturity as the growing season progress (Barne s et al., 2007). Brow n and Mislevy (1988) reported that ADF concentration of bahiagrass increased from June ( 41.8%) to July (46.3%), then remain constant through September (47.1%). Cuomo et al. (1996) examined the chemical composition of bahiagrass at different harvest frequencies during the summer and concluded that ADF concentrations increased from early (m ean=29.9%) to mid-summer (mean=34.0%) at all harvest frequencies. Masticate ADF concentrations were lowest in November (27%), followed by June, July and September (30%), while August and October had the greatest mean concentration of ADF (33%). As for NDF concentration, the lowest AD F concentration occurred in masticate samples

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74 in November, when forage mass began to decrease after the summer. This indicates the steers were selecting forage that was lower in cell wall components compared to other available forage. Duble et al. (1971) concluded that ADF concen tration of warm-season perennial grasses would increase from late spring (A pril to May; mean=34.0%) to early summer (June; mean=35.9%), and remain consistent through mid-summer (Jul y; mean=40.6%). There were no differences between masticate ADF concentration ( P =0.86) for both FA. The SI for ADF concentration was affected by month ( P =0.01), but was not affected by FA ( P =0.99). With the exception of November (-20%), th e SI values indicate that the steers were not selecting forage based on the ADF concentration (mean=-0.3%). Norman et al. (2004) concluded that sheep grazing river saltbush (Atriplex amnicola ) and old man saltbush (Atriplex nummularia) would not show preference for forage ma terial on the basis on ADF concentration. The saltbush species are typically low in nutritive value and grazed only because of proliferance on saline land, not because of palatability or nutritive value of the forage. However, the results of Norman et al. (2004) indicate that the sheep ma y have been selecting forage material based on palatability. During November, the low SI indicate that the steers were se lecting forage 20% less in ADF concentration compared to the hand-clipped samples. This implies that as forage mass was greatest in the summer and fall, the steers selected forage material with less senescence and lower ADF concentration. Implications Results f rom the summer and fall indicate that while bahiagrass matures and its forage mass increases, grazing steers wi ll select forage material with greater IVDOM and CP concentrations, and less NDF and ADF concentra tions. However, hand-collected forage and masticate samples were in excess of cow requirements (NRC, 2000) for energy and protein

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75 during the summer and fall months. The implicat ions of the summer and fall trial are that producers will not need to supplement the cow herd with additional protein or energy.

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76 Table 4-1. Effect of forage availability a nd month on overall mean forage mass (kg/ha). Month P -value FAa June July Aug Sept Oct Nov SEM d FA Month FA*Month H b 2,567 4,689 9,117 12,03210,1069,2921,152 0.03 <0.0010.06 Lc 1,634 3,465 4,897 4,9165,4013,333 aFA= Forage availability. bH = High forage availability. cL= Low forage availability. dSEM= Standard error of mean, n=192. Table 4-2. Effect of sampling type and m onth on chemical composition of bahiagrass. Month P -value Analysis Typea June July Aug Sept Oct Nov SEMe Type Month Type*Month IVDOM b Fc 54.5 51.2 48.154.955.046.21.47 <0.001 <0.001 0.08 M d 58.4 61.1 60.764.563.456.5 CP F 13.9 9.7 8.68.68.68.30.62 <0.001 <0.001 <0.001 M 12.9 12.1 11.09.610.710.1 NDF F 59.1 55.4 61.365.864.863.61.72 <0.001 0.04 <0.001 M 61.4 59.2 57.959.060.951.4 ADF F 28.7 31.1 32.831.334.033.00.75 0.002 <0.001 <0.001 M 30.1 29.7 32.830.232.726.6 DM F 90.4 91.7 90.190.292.390.80.36 0.03 <0.001 <0.001 M 92.1 92.8 90.791.091.190.3 OM F 94.4 94.5 94.794.394.093.00.80 <0.001 0.01 0.07 M 91.2 91.5 91.892.593.689.0 aType= Forage sampling type. bIVDOM= In vitro digestible organic matter. cF= Hand-sampled forage. dM= Masticate. eSEM= Standard error of the mean, n=192.

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77 Table 4-3. Effect of forage availability on chemical analysis of bahiagrass. FAa Analysis H b Lc SEM d P -value Forage IVDOMe 50.5 52.9 0.56 0.09 CP 9.4 9.9 0.20 0.24 NDF 60.4 62.6 1.35 0.37 ADF 31.9 31.8 0.45 0.83 DM 90.8 91.0 0.14 0.49 OM 94.2 94.0 0.24 0.57 Masticate IVDOM 60.1 61.5 0.90 0.39 CP 10.8 11.6 0.27 0.17 NDF 58.4 58.2 0.76 0.93 ADF 30.4 30.3 0.43 0.86 DM 91.3 91.4 0.63 0.82 OM 92.0 91.0 0.44 0.25 aFA= Forage availability. bH= High forage availability. cL= Low forage availability. dSEM= Standard error of the mean, n=96. eIVDOM= In vitro digestible organic matter.

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78 Table 4-4. Effect of forage availability and m onth on steer selection inde x of bahiagrass forage. FA b Month Analysis Hc L d SEMe P -value June July Aug Sept Oct Nov SEMeP -value IVDOM f 120.7 117.1 3.60 0.48 108.4 119.6 126.4 120.4 116.5 122.2 6.08 0.43 CP 118.9 121.6 5.33 0.72 97.1 122.7 128.4 120.6 128.3 124.6 8.99 0.16 NDF 98.7 93.4 2.60 0.16 103.5 112.3 94.8 90.0 94.5 81.5 4.37 0.001 ADF 96.2 96.2 2.69 0.99 105.0 95.4 99.9 98.3 98.1 80.4 4.53 0.01 a{[(Masticate concentration forage concentr ation) / forage concentration] 100} + 100. bFA= Forage availability. cH= High forage availability. dL= Low forage availability. eSEM= Standard error of the mean, n=48. fIVDOM= In vitro diges tible organic matter.

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79 Table 4-5. Precipitation data (cm) Summer and fall 2007. Month Location May June July Aug Sept Oct Nov Ona 30-yr average 1.0 9.8 10.5 19.8 9.1 19.4 21.2 17.8 17.1 17.2 5.2 7.3 0.2 5.3 Brooksville 30-yr average 3.0 8.6 10.8 18.4 22.6 18.2 16.1 20.9 9.4 11.6 16.8 7.5 1.1 5.8 Santa Fe 6.4 16.0 12.711.311.68.01.5 30-yr average Marianna 30-yr average 9.2 5.7 10.7 17.5 5.8 13.3 19.1 7.0 17.6 20.1 10.8 13.7 11.6 3.4 12.1 7.5 12.7 7.4 5.8 5.0 10.5 Table 4-6. Temperature data (0C) Summer and fall 2007. Month Location June July Aug Sept Oct Nov Ona 30-yr average 25.1 26.7 26.0 27.3 26.0 27.3 26.7 26.6 24.7 23.7 18.6 19.9 Brooksville 30-yr average 25.4 26.7 26.1 27.3 27.0 27.2 25.5 26.6 23.6 23.2 17.1 19.7 Santa Fe 24.5 25.9 26.624.421.814.5 30-yr average Marianna 30-yr average 26.3 26.7 25.9 27.2 26.9 27.3 27.1 28.3 26.9 25.6 25.7 24.83 21.1 21.3 19.3 17.0 14.0 14.7

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80 CHAPTER 5 SUMMARY, CONCLUSIONS, AND RE COMMENDATIONS Results of this study indicate that steers gr azing bahiagrass forage during the winter and spring selected forage with greater IVDOM and CP concentrations compared to hand-collected forage samples. The summer and fall results indicate that while bahiagrass matures and its forage mass increases, grazing steers will select forage material with greater IVDOM and CP concentrations, and less NDF and ADF concentrations. Figure 5-1 illustrates the differences in handcollected forage and masticate values for TDN and CP compared to cow requirements for lactation (NRC, 2000). The cow nutrient requirements in Figure 5-1 are based on the NRC (2000) values for a 544 kg cow with 9 kg peak milk with December as the month of parturit ion. During early lactation, bahiagrass forage collected by hand-sampling, as well as bahiagra ss selected by cattle did not meet cow energy requirements; however, masticate and hand-coll ected forage values indicate that CP concentration was not limiting thus cow CP requi rements during the first 4 months of lactation were met by both sampling types. Though later in lactation, both TDN and CP requirements were met by bahiagrass regardless of selection of forage material by either sampling method. When approaching calving (month 11 and 12), ba hiagrass was deficient in TDN, but had CP great enough to meet cow requireme nts during that time period. Intake of TDN is central to the energy status of lactating cattle, which is im portant in maintaining BCS throughout the cows production cycle. This in turn affects repr oductive performance of the cow and further influences the number of calves born, and th e financial outlook for the cattle producer. When given the opportunity, cattle grazing bahi agrass forage will select a diet that is greater in nutritive value compared with hand-c ollected samples, which are normally gathered for estimation of available forage quality. The da ta collected in this study imply that forage

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81 samples collected by hand may under-estimate the nut ritive value of the actual selected forage by cattle. The implications of this study indicate the opportunity to more closely match cow requirements with forage resources, based on available bahiagrass nutritive value and cow selection within those forage opportunities. If less supplement is needed to meet cattle requirements, then the excess supplement currently being provided is excreted by the animal into the environment causing unnecessary nutrient inputs into land and water systems. If energy and protein supplementation can be more closely matc hed to cow requirements, then less N and other nutrient inputs would be added to the envir onment thus improving land and water quality, which is an important concern for Florida cattle producers.

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82 Figure 5-1. Nutrient requirement cycles and pasture characteristics 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 0 2 4 6 8 10 12 14 16 18 123456789101112 Cow TDN Forage TDN Masticate TDN Cow CP Forage CP Masticate CPLbs of CP Lbs of TDN Months Since Calving

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83 APPENDIX A WINTER / SPRING

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84 Table A-1. Effect of forage availability and m onth on overall mean forage mass (kg/ha) at Ona. Month P -value FAa Dec Jan Feb Mar Apr May SEM d FA Month FA*Month H b 5,805 3,840 3,537 2,9712,0607,008663 0.09 <0.0010.17 Lc 2,081 1,339 1,408 1,5011,0954,498 aFA= Forage availability. bH = High forage availability. cL= Low forage availability. dSEM= Standard error of mean, n=48. Table A-2. Effect of sampling t ype and month on chemical com position of bahiagrass at Ona. Month P -value Analysis Typea Dec Jan Feb Mar Apr May SEMe Type Month Type*Month IVDOM b Fc 38.56 34.94 39.0942.8343.7051.292.05 <0.001 <0.001 <0.001 M d 47.80 51.17 58.4156.4565.2558.72 CP F 7.57 9.22 10.9312.0511.7010.840.62 <0.001 <0.001 <0.001 M 9.57 10.56 13.4911.9215.7212.24 NDF F 62.23 63.22 62.4358.6361.0458.251.23 0.006 <0.001 0.18 M 59.41 64.40 58.2253.2856.5357.05 ADF F 32.03 30.87 38.3045.8229.5229.380.89 <0.001 <0.001 <0.001 M 33.23 32.29 28.0827.6028.7126.33 DM F 90.81 91.27 90.9091.1590.6990.680.53 0.01 0.27 0.24 M 91.64 91.22 90.9391.8792.9291.88 OM F 94.50 93.32 94.2793.7893.6494.271.02 <0.001 <0.001 0.004 M 84.64 84.68 88.4284.8290.0391.07 aType= Forage sampling type. bIVDOM= In vitro digestible organic matter. cF= Hand-sampled forage. dM= Masticate. eSEM= Standard error of the mean, n=48.

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85 Table A-3. Effect of forage availability on chemical analysis of bahiagrass at Ona. FAa Analysis H b Lc SEM d P -value Forage IVDOMe 43.62 39.89 2.49 0.39 CP 11.74 9.06 0.50 0.06 NDF 61.18 60.95 0.80 0.86 ADF 32.87 35.81 0.52 0.05 DM 91.81 91.68 0.40 0.83 OM 85.13 89.45 0.77 0.06 Masticate IVDOM 53.10 59.25 1.42 0.09 CP 11.44 13.00 0.57 0.19 NDF 55.33 60.73 0.10 0.06 ADF 26.95 31.76 0.68 0.04 DM 91.32 90.47 0.35 0.22 OM 93.69 94.26 0.39 0.27 aFA= Forage availability. bH= High forage availability. cL= Low forage availability. dSEM= Standard error of the mean, n=24. eIVDOM= In vitro digestible organic matter.

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86 Table A-4. Effect of forage availability and month on steer selection index of ba hiagrass forage at Ona. FA b Month Analysis Hc L d SEMe P -value Dec Jan Feb Mar Apr May SEMeP -value IVDOM f 146.81 125.58 10.95 0.23 122.73 146.45153.78129.85149.22115.1218.96 0.65 CP 143.53 98.94 14.40 0.08 124.98 118.66134.5399.91136.43112.8824.93 0.89 NDF 94.58 95.38 3.45 0.87 93.32 101.8693.3590.6992.7597.815.98 0.78 ADF 98.05 80.29 5.90 0.09 103.64 104.9474.7363.7997.8790.0710.21 0.15 a{[(Masticate concentration forage concentr ation) / forage concentration] 100} + 100. bFA= Forage availability. cH= High forage availability. dL= Low forage availability. eSEM= Standard error of the mean, n=12. fIVDOM= In vitro diges tible organic matter. Table A-5. Effect of forage availability and month on overall mean forage ma ss (kg/ha) at Brooksville. Month P -value FAa Dec Jan Feb Mar Apr May SEM d FA Month FA*Month H b 2,344 1,430 2,521 2,2111,4882,0023990.23 0.15 0.50 Lc 1,603 933 1,065 1,5301,2481,410 aFA= Forage availability. bH = High forage availability. cL= Low forage availability. dSEM= Standard error of mean, n=48.

PAGE 87

87 Table A-6. Effect of sampling type and month on chemical compositi on of bahiagrass at Brooksville. Month P -value Analysis Typea Dec Jan Feb Mar Apr May SEMe Type Month Type*Month IVDOM b Fc 40.43 39.69 38.7344.3650.2650.101.42 <0.001 <0.001 <0.001 M d 52.44 60.08 58.7856.6257.8957.78 CP F 6.78 8.02 8.0610.2010.0610.890.49 <0.001 <0.001 <0.001 M 10.19 12.90 11.4710.3911.6311.63 NDF F 65.19 62.31 64.9661.1961.4861.032.40 <0.001 0.004 0.13 M 65.89 55.10 54.8956.6458.0549.00 ADF F 34.64 32.73 41.1335.6029.1426.511.81 0.003 0.001 <0.001 M 28.32 28.53 28.4633.4935.4925.65 DM F 90.99 91.64 91.0091.1490.6790.850.58 0.03 0.50 0.08 M 90.91 90.66 91.3392.6591.9292.97 OM F 95.56 94.87 95.2294.4694.5694.741.42 <0.001 <0.001 0.004 M 84.09 88.60 89.8383.9676.4788.66 aType= Forage sampling type. bIVDOM= In vitro digestible organic matter. cF= Hand-sampled forage. dM= Masticate. eSEM= Standard error of the mean, n=48.

PAGE 88

88 Table A-7. Effect of forage availability on chem ical analysis of bahi agrass at Brooksville. FAa Analysis H b Lc SEM d P -value Forage IVDOMe 41.95 45.90 0.72 0.06 CP 9.57 8.43 0.32 0.13 NDF 62.39 63.00 1.11 0.73 ADF 33.48 33.11 0.54 0.67 DM 91.21 90.87 0.14 0.23 OM 94.87 94.96 0.16 0.70 Masticate IVDOM 54.24 60.29 0.91 0.04 CP 10.82 11.92 0.47 0.24 NDF 52.08 61.11 3.28 0.19 ADF 26.55 33.43 1.99 0.13 DM 92.35 91.14 0.77 0.38 OM 80.77 89.69 1.40 0.05 aFA= Forage availability. bH= High forage availability. cL= Low forage availability. dSEM= Standard error of the mean, n=24. eIVDOM= In vitro digestible organic matter.

PAGE 89

89 Table A-8. Effect of forage availability and month on st eer selection index of bahiagrass forage at Brooksville. FA b Month Analysis Hc L d SEMe P -value Dec Jan Feb Mar Apr May SEMeP -value IVDOM f 137.82 126.61 3.88 0.10 129.68 151.72151.79127.67115.74116.706.72 0.04 CP 147.20 116.05 11.29 0.11 150.24 167.84147.56101.84115.55106.7119.55 0.24 NDF 89.89 90.52 5.38 0.94 101.08 88.96 84.4492.5394.0180.229.33 0.67 ADF 87.56 96.19 11.11 0.61 81.77 87.67 69.1794.26121.6196.7719.25 0.58 a{[(Masticate concentration forage concentr ation) / forage concentration] 100} + 100. bFA= Forage availability. cH= High forage availability. dL= Low forage availability. eSEM= Standard error of the mean, n=12. fIVDOM= In vitro diges tible organic matter. Table A-9. Effect of forage availability and mont h on overall mean forage mass (kg/ha) at Santa Fe. Month P -value FAa Dec Jan Feb Mar Apr May SEM d FA Month FA*Month H b 1,821 1,120 1,507 1,4681,3103,9744290.09 0.02 0.19 Lc 1,052 971 1,0411,0591,642 aFA= Forage availability. bH = High forage availability. cL= Low forage availability. dSEM= Standard error of mean, n=48.

PAGE 90

90 Table A-10. Effect of sampling type and month on chemical compositi on of bahiagrass at Santa Fe. Month P -value Analysis Typea Dec Jan Feb Mar Apr May SEMe Type Month Type*Month IVDOM b Fc 43.66 39.3255.8451.8150.422.62 <0.001 <0.0010.01 M d 51.46 63.2763.6357.0861.57 CP F 7.70 11.9115.2013.7513.270.89 0.18 <0.0010.43 M 9.83 14.5614.7215.0713.55 NDF F 64.98 61.2049.6752.5156.271.98 <0.001 <0.0010.05 M 60.87 46.8943.8247.0854.20 ADF F 31.83 39.3427.9527.9425.432.27 0.02 0.01 0.004 M 35.14 23.9123.1828.4725.56 DM F 91.80 90.4789.7290.8090.370.39 <0.001 0.007 0.002 M 92.10 90.8191.5091.7393.62 OM F 95.51 95.3992.8593.6894.722.04 <0.001 0.30 0.05 M 80.63 86.4487.2091.3688.19 aType= Forage sampling type. bIVDOM= In vitro digestible organic matter. cF= Hand-sampled forage. dM= Masticate. eSEM= Standard error of the mean, n=48.

PAGE 91

91 Table A-11. Effect of forage availability on ch emical analysis of bahiagrass at Santa Fe. FAa Analysis H b Lc SEM d P -value Forage IVDOMe 48.02 48.40 2.32 0.92 CP 12.82 11.91 0.76 0.49 NDF 54.34 59.51 1.32 0.11 ADF 29.47 31.52 2.47 0.43 DM 90.54 90.72 0.19 0.57 OM 94.33 94.52 0.39 0.77 Masticate IVDOM 59.04 59.76 1.26 0.73 CP 13.29 13.81 0.79 0.69 NDF 50.48 50.66 0.73 0.87 ADF 27.23 27.27 1.43 0.98 DM 92.27 91.63 0.58 0.51 OM 86.51 87.01 1.45 0.83 aFA= Forage availability. bH= High forage availability. cL= Low forage availability. dSEM= Standard error of the mean, n=24. eIVDOM= In vitro digestible organic matter.

PAGE 92

92 Table A-12. Effect of forage availability and month on st eer selection index of bahi agrass forage at Santa Fe. FA b Month Analysis Hc L d SEMe P -value Dec Jan Feb Mar Apr May SEMeP -value IVDOM f 122.28 133.31 4.22 0.12108.78149.30161.63114.36110.47122.256.180.02 CP 120.52 110.09 14.58 0.62136.06124.90122.1796.84109.80102.0821.340.79 NDF 94.78 84.15 4.31 0.1391.0492.8776.8088.4690.6996.926.310.47 ADF 101.86 85.52 7.01 0.15110.71102.8360.9582.96102.21102.4910.270.14 a{[(Masticate concentration forage concentr ation) / forage concentration] 100} + 100. bFA= Forage availability. cH= High forage availability. dL= Low forage availability. eSEM= Standard error of the mean, n=12. fIVDOM= In vitro diges tible organic matter. Table A-13. Effect of forage availability and mont h on overall mean forage mass (kg/ha) at Marianna. Month P -value FAa Dec Jan Feb Mar Apr May SEM d FA Month FA*Month H b 1,263 1,810 995 8181,0382,096308 0.12 0.04 0.42 Lc 455 535 753 7875811,552 aFA= Forage availability. bH = High forage availability. cL= Low forage availability. dSEM= Standard error of mean, n=48.

PAGE 93

93 Table A-14. Effect of sampling type and month on chemical compositi on of bahiagrass at Marianna. Month P -value Analysis Typea Dec Jan Feb Mar Apr May SEMe Type Month Type*Month IVDOM b Fc 54.68 35.04 50.8054.8854.4950.192.23 <0.001 <0.001 0.06 M d 66.34 54.56 69.5161.9960.1563.65 CP F 9.03 9.75 12.1610.3611.479.830.56 <0.001 <0.001 0.08 M 12.00 11.70 14.2410.5711.8912.61 NDF F 56.82 61.99 51.8346.6355.0061.471.85 <0.001 <0.001 0.004 M 50.70 66.35 39.2939.9248.0155.36 ADF F 25.97 32.20 38.3029.5031.3134.061.04 <0.001 <0.001<0.001 M 25.64 34.80 22.9224.9027.0828.96 DM F 91.18 91.01 90.2190.6889.8691.030.32 0.06 <0.001 <0.001 M 89.47 91.46 90.4991.5489.8393.96 OM F 93.09 95.01 93.0594.0992.8593.990.97 <0.001 <0.001 <0.001 M 85.99 77.57 86.3791.0388.6992.34 aType= Forage sampling type. bIVDOM= In vitro digestible organic matter. cF= Hand-sampled forage. dM= Masticate. eSEM= Standard error of the mean, n=48.

PAGE 94

94 Table A-15. Effect of forage availability on ch emical analysis of ba hiagrass at Marianna. FAa Analysis H b Lc SEM d P -value Forage IVDOMe 52.78 48.25 1.92 0.23 CP 11.60 9.27 0.40 0.03 NDF 54.15 57.09 1.59 0.32 ADF 31.51 32.27 0.83 0.58 DM 90.52 90.80 0.18 0.40 OM 93.59 93.77 0.51 0.83 Masticate IVDOM 63.52 62.18 1.47 0.57 CP 13.61 10.73 0.40 0.04 NDF 48.49 51.38 0.87 0.14 ADF 25.82 28.95 0.69 0.09 DM 91.28 91.01 0.11 0.23 OM 88.99 85.00 0.73 0.06 aFA= Forage availability. bH= High forage availability. cL= Low forage availability. dSEM= Standard error of the mean, n=24. eIVDOM= In vitro digestible organic matter.

PAGE 95

95 Table A-16. Effect of forage availability and month on st eer selection index of bahi agrass forage at Marianna. FA b Month Analysis Hc L d SEMe P -value Dec Jan Feb Mar Apr May SEMeP -value IVDOM f 123.94 128.94 4.65 0.49 121.72 155.43137.30112.87104.30126.988.11 0.05 CP 113.87 120.90 5.18 0.38 134.69 118.00116.28102.07103.91129.388.96 0.21 NDF 88.81 88.80 4.24 0.99 89.17 107.0875.4484.3087.0689.777.34 0.23 ADF 83.00 90.25 9.20 0.60 98.22 108.3059.5281.7485.9285.3515.83 0.46 a{[(Masticate concentration forage concentr ation) / forage concentration] 100} + 100. bFA= Forage availability. cH= High forage availability. dL= Low forage availability. eSEM= Standard error of the mean, n=12. fIVDOM= In vitro diges tible organic matter.

PAGE 96

96 APPENDIX B SUMMER / FALL

PAGE 97

97 Table B-1. Effect of forage availability and m onth on overall mean forage mass (kg/ha) at Ona. Month P -value FAa June July Aug Sept Oct Nov SEM d FA Month FA*Month H b 4,298 6,042 11,773 19,40414,68017,7621,880 0.02 0.0050.03 Lc 3,020 4,081 5,576 6,1245,5883,798 aFA= Forage availability. bH = High forage availability. cL= Low forage availability. dSEM= Standard error of mean, n=48. Table B-2. Effect of sampling t ype and month on chemical com position of bahiagrass at Ona. Month P -value Analysis Typea June July Aug Sept Oct Nov SEMe Type Month Type*Month IVDOM b Fc 48.69 50.91 44.3343.6751.6345.111.31 <0.001 <0.001 <0.001 M d 54.90 56.59 56.9668.1369.5359.74 CP F 9.83 8.86 6.878.777.257.530.45 <0.001 <0.001 0.004 M 10.08 8.69 8.5712.5711.1010.65 NDF F 60.18 61.18 61.5267.5664.7863.491.67 <0.001 0.01 <0.001 M 64.14 64.68 57.4054.3052.5851.24 ADF F 30.17 31.48 33.5835.9435.0734.471.03 <0.001 0.12 <0.001 M 31.23 34.13 32.4728.0829.9427.80 DM F 90.26 91.92 91.0491.7692.2891.110.85 0.18 0.08 0.04 M 92.14 93.22 89.2591.4388.9789.47 OM F 95.29 94.29 94.8593.7493.7689.000.98 <0.001 <0.001 0.008 M 94.34 91.81 88.4393.0092.3581.98 aType= Forage sampling type. bIVDOM= In vitro digestible organic matter. cF= Hand-sampled forage. dM= Masticate. eSEM= Standard error of the mean, n=48.

PAGE 98

98 Table B-3. Effect of forage availability on chemical analysis of bahiagrass at Ona. FAa Analysis H b Lc SEM d P -value Forage IVDOMe 43.62 51.17 0.44 0.007 CP 8.00 8.38 0.14 0.20 NDF 62.40 63.83 0.33 0.09 ADF 33.41 33.59 0.76 0.88 DM 91.30 91.49 0.15 0.48 OM 94.10 92.87 0.39 0.16 Masticate IVDOM 59.46 62.49 0.88 0.13 CP 9.81 10.74 0.26 0.13 NDF 56.89 57.98 2.50 0.79 ADF 30.04 31.17 0.82 0.43 DM 90.08 91.41 0.65 0.29 OM 91.75 88.89 0.58 0.07 aFA= Forage availability. bH= High forage availability. cL= Low forage availability. dSEM= Standard error of the mean, n=24. eIVDOM= In vitro digestible organic matter.

PAGE 99

99 Table B-4. Effect of forage availability and month on steer selection index of ba hiagrass forage at Ona. FA b Month Analysis Hc L d SEMe P -value June July Aug Sept Oct Nov SEMeP -value IVDOM f 137.24 122.68 4.66 0.08 113.76111.15129.22157.49136.13132.018.060.07 CP 123.67 132.18 10.80 0.60 103.5097.23123.75148.46153.15141.4718.710.31 NDF 91.64 91.24 2.68 0.93 105.61105.7293.3680.3981.5780.884.960.03 ADF 90.79 93.93 4.92 0.67 103.90109.0496.8078.1485.6580.638.540.20 a{[(Masticate concentration forage concentr ation) / forage concentration] 100} + 100. bFA= Forage availability. cH= High forage availability. dL= Low forage availability. eSEM= Standard error of the mean, n=12. fIVDOM= In vitro diges tible organic matter. Table B-5. Effect of forage availability and month on overall mean forage ma ss (kg/ha) at Brooksville. Month P -value FAa June July Aug Sept Oct Nov SEM d FA Month FA*Month H b 1,088 9,730 9,45812,83011,9181,741 0.05 0.0090.33 Lc 1,073 5,796 4,1646,4584,522 aFA= Forage availability. bH = High forage availability. cL= Low forage availability. dSEM= Standard error of mean, n=48.

PAGE 100

100 Table B-6. Effect of sampling type and month on chemical compositi on of bahiagrass at Brooksville. Month P -value Analysis Typea June July Aug Sept Oct Nov SEMe Type Month Type*Month IVDOM b Fc 54.18 48.0754.6449.6545.592.08 <0.001 0.009 0.42 M d 61.39 59.7462.3361.3151.21 CP F 12.24 8.396.937.696.890.42 <0.001 <0.001 0.17 M 13.34 10.929.8610.379.49 NDF F 60.90 61.8066.5968.2863.901.10 <0.001 <0.001 <0.001 M 59.64 57.8957.2863.6847.86 ADF F 27.98 34.0933.0737.9433.720.41 <0.001 <0.001<0.001 M 29.16 34.1530.7336.6826.75 DM F 90.73 90.1890.2493.4290.940.14 0.01 <0.001 <0.001 M 91.82 91.2791.2791.2291.26 OM F 94.80 94.4194.7493.9794.251.26 0.001 0.51 0.38 M 92.07 91.7391.2995.2389.79 aType= Forage sampling type. bIVDOM= In vitro digestible organic matter. cF= Hand-sampled forage. dM= Masticate. eSEM= Standard error of the mean, n=48.

PAGE 101

101 Table B-7. Effect of forage availability on chem ical analysis of bahi agrass at Brooksville. FAa Analysis H b Lc SEM d P -value Forage IVDOMe 50.84 50.74 0.85 0.94 CP 8.27 8.58 0.34 0.58 NDF 63.98 64.61 0.20 0.15 ADF 33.53 33.19 0.23 0.46 DM 90.91 91.29 0.08 0.08 OM 94.20 94.66 0.14 0.14 Masticate IVDOM 60.01 58.75 1.57 0.61 CP 11.06 10.50 0.31 0.32 NDF 54.81 59.87 1.65 0.16 ADF 30.65 32.37 0.75 0.14 DM 91.47 91.34 0.15 0.58 OM 90.91 93.11 0.90 0.21 aFA= Forage availability. bH= High forage availability. cL= Low forage availability. dSEM= Standard error of the mean, n=24. eIVDOM= In vitro digestible organic matter.

PAGE 102

102 Table B-8. Effect of forage availability and month on st eer selection index of bahiagrass forage at Brooksville. FA b Month Analysis Hc L d SEMe P -value June JulyAug Sept Oct Nov SEMeP -value IVDOM f 118.33 115.11 1.20 0.32 113.29. 124.29110.38 123.32112.333.16 0.09 CP 137.77 123.92 6.44 0.20 108.97. 129.94142.12 135.50137.7010.18 0.32 NDF 85.75 92.36 1.42 0.03 97.95. 93.6886.01 92.8574.182.25 0.01 ADF 91.89 97.42 3.08 0.27 104.18. 100.3193.02 96.4879.294.87 0.11 a{[(Masticate concentration forage concentr ation) / forage concentration] 100} + 100. bFA= Forage availability. cH= High forage availability. dL= Low forage availability. eSEM= Standard error of the mean, n=12. fIVDOM= In vitro diges tible organic matter. Table B-9. Effect of forage availability and mont h on overall mean forage mass (kg/ha) at Santa Fe. Month P -value FAa June July Aug Sept Oct Nov SEM d FA Month FA*Month H b 3,579 4,947 5,338 9,8823,8303,634439 0.02 <0.001<0.001 Lc 1,507 3,951 4,027 2,9643,7162,524 aFA= Forage availability. bH = High forage availability. cL= Low forage availability. dSEM= Standard error of mean, n=48.

PAGE 103

103 Table B-10. Effect of sampling type and month on chemical compositi on of bahiagrass at Santa Fe. Month P -value Analysis Typea June July Aug Sept Oct Nov SEMe Type Month Type*Month IVDOM b Fc 59.23 52.23 49.0257.9862.6447.991.84 <0.001 <0.001<0.001 M d 53.46 59.09 61.8763.4561.7355.67 CP F 15.35 9.70 10.6210.6210.168.690.29 0.004 <0.001<0.001 M 11.64 13.70 12.008.9811.499.98 NDF F 57.31 61.57 61.1567.3363.5863.630.58 <0.001 <0.001<0.001 M 60.28 61.32 61.5060.3665.9647.51 ADF F 27.85 32.01 30.4729.4332.0531.920.68 0.36 <0.001<0.001 M 31.49 29.39 33.2730.8133.5523.04 DM F 89.66 91.87 89.4890.6791.5191.080.26 0.008 <0.001<0.001 M 91.43 92.73 91.3190.7691.6689.29 OM F 94.27 95.06 94.6294.5894.1394.130.26 <0.001 <0.001<0.001 M 86.08 92.08 93.3592.8294.3092.20 aType= Forage sampling type. bIVDOM= In vitro digestible organic matter. cF= Hand-sampled forage. dM= Masticate. eSEM= Standard error of the mean, n=48.

PAGE 104

104 Table B-11. Effect of forage availability on ch emical analysis of ba hiagrass at Santa Fe. FAa Analysis H b Lc SEM d P -value Forage IVDOMe 54.58 55.11 1.07 0.76 CP 10.88 10.83 0.22 0.90 NDF 63.07 61.80 0.56 0.25 ADF 30.62 30.62 0.65 0.99 DM 90.65 90.78 0.15 0.61 OM 94.55 94.37 0.03 0.06 Masticate IVDOM 57.85 60.58 0.99 0.19 CP 11.33 11.27 0.14 0.80 NDF 60.59 59.48 0.50 0.26 ADF 30.00 30.52 0.29 0.33 DM 91.57 90.82 0.19 0.11 OM 92.59 91.02 0.16 0.02 aFA= Forage availability. bH= High forage availability. cL= Low forage availability. dSEM= Standard error of the mean, n=24. eIVDOM= In vitro digestible organic matter.

PAGE 105

105 Table B-12. Effect of forage availability and month on st eer selection index of bahi agrass forage at Santa Fe. FA b Month Analysis Hc L d SEMe P -value June July Aug Sept Oct Nov SEMeP -value IVDOM f 107.78 110.36 3.84 0.65 90.79113.14126.00109.5398.78116.176.640.09 CP 110.60 105.27 8.80 0.69 79.07140.93112.2186.90113.05115.4715.240.21 NDF 96.38 96.25 2.48 0.97 105.0899.54 100.4994.53103.7374.504.300.03 ADF 98.43 100.02 3.02 0.72 113.1591.75 109.17104.60104.6872.005.220.02 a{[(Masticate concentration forage concentr ation) / forage concentration] 100} + 100. bFA= Forage availability. cH= High forage availability. dL= Low forage availability. eSEM= Standard error of the mean, n=12. fIVDOM= In vitro diges tible organic matter. Table B-13. Effect of forage availability and mont h on overall mean forage mass (kg/ha) at Marianna. Month P -value FAa June July Aug Sept Oct Nov SEM d FA Month FA*Month H b 1,304 3,079 9,603 9,3829,0823,856979 0.05 <0.0010.18 Lc 936 2,363 4,192 6,4145,8422,478 aFA= Forage availability. bH = High forage availability. cL= Low forage availability. dSEM= Standard error of mean, n=48.

PAGE 106

106 Table B-14. Effect of sampling type and month on chemical compositi on of bahiagrass at Marianna. Month P -value Analysis Typea June July Aug Sept Oct Nov SEMe Type Month Type*Month IVDOM b Fc 55.82 50.41 50.8761.4956.1546.091.43 <0.001 <0.001<0.001 M d 63.97 67.69 64.1264.1261.3359.33 CP F 17.30 10.58 8.828.489.4110.000.43 <0.001 <0.001<0.001 M 16.72 13.65 12.878.8310.6210.49 NDF F 59.12 45.01 60.1559.5462.1261.044.38 0.84 0.15 0.61 M 61.54 53.80 54.9358.9561.9258.39 ADF F 28.80 29.73 33.1526.8130.7631.930.79 0.39 <0.001<0.001 M 28.49 25.48 30.9331.5532.1428.77 DM F 90.95 91.45 89.7988.0492.1289.900.25 <0.001 <0.0010.004 M 93.13 92.46 90.8490.4492.3191.17 OM F 92.89 94.25 94.4494.4293.8894.130.26 <0.001 <0.001<0.001 M 92.03 90.74 93.3592.9593.3592.67 aType= Forage sampling type. bIVDOM= In vitro digestible organic matter. cF= Hand-sampled forage. dM= Masticate. eSEM= Standard error of the mean, n=48.

PAGE 107

107 Table B-15. Effect of forage availability on ch emical analysis of ba hiagrass at Marianna. FAa Analysis H b Lc SEM d P -value Forage IVDOMe 52.66 54.28 0.90 0.33 CP 10.24 11.28 0.26 0.10 NDF 54.88 60.78 3.29 0.33 ADF 30.20 30.20 0.91 0.99 DM 90.37 90.38 0.13 0.98 OM 93.96 94.04 0.16 0.75 Masticate IVDOM 62.93 63.92 0.91 0.52 CP 10.92 13.48 0.32 0.29 NDF 60.24 56.28 1.41 0.19 ADF 31.29 27.83 0.37 0.02 DM 91.81 91.64 0.11 0.37 OM 92.82 92.21 0.31 0.30 aFA= Forage availability. bH= High forage availability. cL= Low forage availability. dSEM= Standard error of the mean, n=24. eIVDOM= In vitro digestible organic matter.

PAGE 108

108 Table B-16. Effect of forage availability and month on st eer selection index of bahi agrass forage at Marianna. FA b Month Analysis Hc L d SEMe P -value June July Aug Sept Oct Nov SEMeP -value IVDOM f 119.68 118.09 7.41 0.96 115.83134.53126.02104.03107.78128.1212.840.55 CP 106.99 124.53 5.85 0.09 96.82130.03147.61104.75111.63103.7110.130.09 NDF 114.64 92.62 6.57 0.06 104.29131.6391.4498.8699.9295.6311.370.31 ADF 103.85 92.93 4.56 0.15 98.9185.48 93.46117.30105.4289.807.900.21 a{[(Masticate concentration forage concentr ation) / forage concentration] 100} + 100. bFA= Forage availability. cH= High forage availability. dL= Low forage availability. eSEM= Standard error of the mean, n=12. fIVDOM= In vitro diges tible organic matter.

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109 LITERATURE CITED Acosta, R. A. and M. M. Kothm ann. 1978. Chemi cal composition of esophageal-fistula forage samples as influenced by drying method a nd salivary leaching. J. Anim. Sci. 47:691-698. Adams, W. E. ,and M. Stelly. 1958. A compar ison of Coastal and Common bermudagrasses ( Cynodon dactylon (L.) Pers.) in the Piedmont Region: I. Yield response to fertilization. Agron J. 50:457-459. Adams, W. E., M. Stelly, H. D. Morris, and C. B. Elkins. 1967. A comparison of Coastal and common bermudagrasses ( Cynodon dactylon (L.) Pers.) in the Pied mont region. II. Effect of fertilization and crimson clover ( Trifolium incarnatum ) on nitrogen phosphorus, and potassium contents of the forage. Agron J. 59:281-284. Anderson, B., J. K. Ward, K. P. Vogel, M. G. Wa rd, H. J. Gorz, and F. A. Haskins. 1988. Forage quality and performance of yearlings grazing switchgrass strains se lected for differing digestibility. J. Anim. Sci. 66:2239-2244. AOAC. 2007. Official Met hods of Analysis. 18th ed. Associ ation of Official Analytical Chemists, Arlington, VA. Arnold, G. W. and M. L. Dudzinski. 1978. Etiology of Free-Ranging Domestic Animals. Elsevier Scientific P ubl. Co., Brooklyn, New York. Arthington, J. D., and W. F. Brown. 2005. Estimati on of feeding value of four tropical forage species at two stages of matu rity. J. Anim. Sci. 83:1726-1731. Bailey, D. W. 1995. Daily selection of f eeding areas by cattle in homogeneous and heterogeneous environments. A ppl. Anim. Behav. Sci. 45:183-200. Ball, D. M., C. S. Hoveland, and G. D. Lacefield. 2002. Southern forages, 3rd Ed. Modern concepts for forage crop management. Potash & Phosphate Institute and the Foundation for Agronomic Research, Norcross, GA. Barnes, R. F., C. J. Nelson, K. J. Moore, M. Collis {eds.}. 2007. Forages: The Science of Grassland Agriculture. Iowa State University Press. Ames, IA. Barton, II, F. E., H. E. Amos, D. Burdick, and R. L. Wilson. 1976. Relationship of chemical analysis to in vitro digestibility for selected tropical and temperate grasses. J. Anim. Sci. 43(2):504-512. Beaty, E. R., R. L. Stanley, and J. Powell. 1968. E ffect of height of cut on yield of Pensacola bahiagrass. Agron. J. 60:356-358. Bennett, L. L., A. C. Hammond, M. J. Williams, C. C. Chase Jr., and W. E. Kunkle. 1999. Diet selection by steers using microhi stological and stable carbon isotope ratio analyses. J. Anim. Sci. 77:2252-2258.

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110 Bertrand, J. E., and L. S. Dunavin. 1985. Grazing evaluation of two hybrid bermudagrasses, Callie bermudagrass and Pensacola bahiagrass in North Florida. Pages 67-70 in Florida Beef Cattle Res. Rep. Univ. of Florida, Gainesville. Birkelo, C. P., D. E. Johnson, and H. P. Phe tteplace. 1991. Maintenance requirements of beef cattle as affected by season on different pl anes of nutrition. J. Anim. Sci. 69:1214-1222. Blackstone, J. B., R. W. Rice, and W. M. Johnson. 1965. A study of the esophageal fistula sampling technique. Proc. West. Sec. Amer. Soc. Anim. Sci. 16:75. Brown, W. E., J. M. Spiers, and C. W. T hurman. 1976. Performance of five warm-season perennial grasses grown in southe rn Mississippi. Agron. J. 68:821-823. Brown, R. H. 1985. Growth of C3 and C4 grasses under low N levels. Crop Sci. 25:954-957. Brown, W. F., and M. B. Adjei. 2001. Urea and/ or feather meal supplementation for yearling steers grazing limpograss (Hemarth ria altissima var. 'Floralta' ) pasture. J. Anim. Sci. 79:3170-3176. Brown, W. F., and P. Mislevy. 1988. Influence of maturity and seas on on the yield and quality of tropical grasses. Pages 46 in Florida Beef Cattle Res. Rep. Univ. of Florida, Gainesville. Brown, W. F., J. D. Phillips, and D. B. Jones. 1987. Ammoniation or cane molasses supplementation of low quality forages. J. Anim. Sci. 64:1205-1214. Burns, J. C. 2006. Grazing research in the humid East: A historical perspective. Crop Sci. 46:118-130. Burton, G. W. 1967. A search for the origin of Pensacola bahiagrass. Econ. Bot. 21:379-382. Burton, G. W., G. M. Prine, and J. E. Jackson. 1957. Studies of drouth tolerance and water use of several Southern grasses. Agron. J. 49:498-503. Carroll, F. D., D. D. Nelson, H. Wolf, and G. Plange. 1964. Energy utilization in heifers as affected by a low-protein isocalor ic diet. J. Anim. Sci. 23:758-763. Cassard, D. W., and E. M. Juergenson. 1971. A pproved Practices in Feeds and Feeding. 4th ed. The Interstate Printers and Publishers. Danville, IL. Chambliss, C. G., F. A. Johnson, and M. B. Adjei. 2006. Bermudagrass production in Florida (SS-AGR-60). Gainesville: University of Fl orida Institute of Food and Agricultural Sciences. Retrieved September 29, 2008, from http://edis.ifas.ufl.edu/AA220.

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111 Chambliss, C. G., and L. E. Sollenberger. 1991. Bahiagrass: The foundation of cow-calf nutrition in Florida. In: 40th Annual Florida Beef Cattle Short Course, Univ. of Florida, Gainesville. p 74-80. Chapman, H. D., W. H. Marchant, P. R. Utley, R. E. Hellwig, and W. G. Monson. 1972. Performance of steers on Pensacola bahiagra ss Coastal bermudagrass, and Coastcross-1 bermudagrass pastures and pellets J. Anim. Sci. 34(3):373-378. Chizzoti, M. L., S. C. Valadares Filho, L. O. Te deschi, F. H. M. Chizzoti, and G. E. Carstens. 2007. Energy and protein requirements for grwoth and maintenance of F1 Nellore x Red Angus bulls, steers, and heifer. J. Anim. Sci. 85:1971-1981. Chizzotti, M. L., L. O. Tedeschi, and S. C. Valadares Filho. 2008. A meta-analysis of energy and protein requirements for maintenance and gr owth of Nellore cattle. J. Anim. Sci. 86:1588-1597. Coleman, S. W., and K. M. Barth. 1973. Quality of diets selected by gr azing animals and its relation to quality of available forage and sp ecies composition of pastures. J. Anim. Sci. 36:754-761. Connor, J. M., V. R. Bohman, A. L. Lesperance, and F. E. Kinsinger. 1963. Nutritive evaluation of summer range forage with cattle. J. Anim. Sci. 22:961-969. Corbett, J. L., M. Freer, and M. M. Graham. 19 85. A generalized equation to predict the varying maintenance metabolism of sheep and cattle. Energy Metab. Proc. Symp. 32:62-65. Cullison, A. E. 1975. Feeds and feeding. Reston Publishing Company, Inc. Reston, VA. Cuomo, G. J., D. C. Blouin, D. L. Corkern, J. E. McCoy, and R. Walz. 1996. Plant morphology and forage nutritive value of three bahiagra sses as affected by harvest frequency. Agron. J. 88:85-89. Davis, C. E., V. D. Jolley, G. D. Mooso, L. R. Robison, and R. D. Horrocks. 1989. Quality of stockpiled limpograss forage at varying fertility levels. Agron. J. 79:229-235. Delfino, J. G. and G. W. Mathison. 1991. Effects of cold environment and intake level on the energetic efficiency of feedlot steers. J. Anim. Sci. 69:4577-4587. Dubbs, T. M., E. S. Vanzant, S. E. Kitts, R. F. Bapst, B. G. Fieser, and C. M. Howlett. 2003. Characterization of season and sampling method effects on measurement of forage quality in fescue-based past ures. J. Anim. Sci. 81:1308-1315. Duble, R. L., J. A. Lancaster, and E. C. Holt. 1971. Forage characteristics limiting animal performance on warm-season perennial grasses. Agron. J. 63:795-798.

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117 Thompson, W. R., J. C. Meiske, R. D. Goodrich, J. R. Rust, and F. M. Byers. 1983. Influence of body composition on energy requirements of beef cows during winter. J. Anim. Sci. 56:1241-1252. Thonney, M. L., R. W. Touchberry, R. D. Goodr ich, and J. C. Meiske. 1976. Intraspecies relationship between fasting heat produc tion and body weight: A reevaluation of W.75. J. Anim. Sci. 43:692-704. Tilley, J. M. A. and R. A. Terry. 1963. A two-stage technique for the in vitro digestion of forage crops. J. Br. Grassland Soc. 18:104-111. USDA, National Agricultural Statistics Servic e, Florida Field Offi ce. 2007. Livestock County estimates. Orlando, FL: U. S. Department of Agriculture. http://www.usda.gov/wps/portal/!ut/p/_ s.7_0_A/7_0_1OB?navid=SEARCH&mode=sim ple&q=florida+livestock+county+estimate&x= 0&y=0&site=usda. Accessed October 2, 2008. Utley, P. R., H. D. Chapman, W. G. Monson, W. H. Marchant, and W. C. McCormick. 1974. Coastcross-1 bermudagrass, Coastal bermuda grass and Pensacola bahiagrass as summer pasture for steers. J. Anim. Sci. 38:490-495. Van Es, A. J. H. 1972. Maintenance. in: W. Lenkeit, K. Breirem and E. Crasemann (Ed.) Hanbuch der Tierernahrung. pp.1-54. Paul Parey, Hamburg. Van Soest, P. J., J. B. Robertson, and B. A. Lewis. 1991. Methods for dietary fiber, neutral detergent fiber, and nonstarch polysaccharides in relation to animal nutrition. J. Dairy Sci. 74:2773-2784. Vermorel, M., J. C. Bouvier, and Y. Geay. 1980. Energy utilization by growing calves: Effect of age, milk intake, and feed level. Energy Metab. Proc. Symp. 26:9-53. Villapando, R. R., and D. A. Graetz. 2001. Phosphor us sorption and desorption properties of the spodic horizon from selected Florida spodos ols. Soil Sci. Soc. Am. J. 65:331-339. Warrington, B. G., F. M. Byers, G. T. Schelling, D. W. Forrest, J. F. Baker, and L. W. Greene. 1988. Gestation nutrition, tissue exchange and maintenance requirements of heifers. J. Anim. Sci. 66:774-782. Waterman, R. C., E. E. Grings, T. W. Geary, A. J. Roberts, L. J. Alexander, and M. D. MacNeil. 2007. Influence of seasonal forage quality on glucose kinetics of young beef cows. J. Anim. Sci. 85:2582-2595. Weir, W. C., and D. T. Torrell. 1959. Selectiv e grazing by sheep as shown by a comparison of the chemical composition of range and pastur e forage obtained by hand clipping and that collected by esophageal-fistulate d sheep. J. Anim. Sci. 18:641-649.

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119 BIOGRAPHICAL SKETCH Ashley Lynn Hughes was born in 1984, in Tampa, FL. She lived in Miam i, FL, until the age of 14, and then moved to a beef cattle ranc h in Okeechobee, FL. While living and working on the ranch, she developed an interest in the beef cattle industry. This prompted her to begin an undergraduate degree in animal sc iences at the University of Florida in 2002 after graduating from Okeechobee High School. Midway through her te nure at UF, Ashley decided to change her major to food and resource economics, since she wished to attend culinary school after graduation. However, her employment in the dairy and ruminant nutrition labs as an undergraduate influenced her to remain in the an imal science industry. After graduating with her B. S. degree in 2006, she immediately began work ing toward a masters degree in beef cattle nutrition. During her studies, Ashley was i nvolved with Gator Collegiate Cattlewomen, Dairy Science Club, Agricultural and Life Sciences College Council, Board of College Councils, and the Animal Science Graduate Student Association. As a University of Florida student, Ashley cultivated a love of the Florid a Gators and has been proud to cel ebrate their football and two basketball national championships. Upon completion of her masters degree, Ashley will begin a career at the Georgia Beef Board.