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Management of Brachiaria Cultivar Mulato in South Florida

Permanent Link: http://ufdc.ufl.edu/UFE0024523/00001

Material Information

Title: Management of Brachiaria Cultivar Mulato in South Florida
Physical Description: 1 online resource (82 p.)
Language: english
Creator: Inyang, Uduak
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: accumulation, animal, average, bahiagrass, brachiaria, crude, cultivar, daily, defoliation, digestibility, gain, hectare, height, herbage, hybrid, interval, mass, mulato, nutritive, performance, persistence, protein, rates, regrowth, stocking, stubble, value, yield
Agronomy -- Dissertations, Academic -- UF
Genre: Agronomy thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Bahiagrass (Paspalum notatum Fl?gge) is the most planted forage in Florida covering approximately 2.5 million acres. Nonetheless, loss of stands due to mole crickets indicates a need for other grass species adapted to south Florida. Brachiariagrasses are the most widely grown warm-season forage in tropical America. Mulato is the first hybrid in the Brachiaria genus and results from crossing ruzigrass (Brachiaria ruziziensis clone 44-6) and palisadegrass (Brachiaria brizantha CIAT 6297). This new cultivar is known for its tolerance of prolonged drought and superior nutritive value, but its response to defoliation is unknown. Two field experiments were conducted to determine the yield, animal performance, and nutritive value of Mulato under varied management intensities and in comparison with bahiagrass. The experiments were conducted at the Range Cattle Research and Education Center, Ona, FL. The first experiment tested the effect of three stocking rates 4, 8, and 12 heifers (LW = 350 ? 21 kg) ha-1 on animal performance and herbage production of Mulato and bahiagrass pastures. There was an increase in herbage yield but a decrease in herbage allowance with increasing stocking rates. Mulato had greater herbage accumulation, crude protein, and digestibility than bahiagrass. Heifers grazing bahiagrass and Mulato pastures had lower daily gain at 12 heifers ha-1 but there was no difference between grasses at stocking rates of 4 and 8 heifers ha-1. Gain per hectare (GHA) and herbage accumulation (HMA) were greatest for Mulato pastures stocked at 8 heifers ha-1. The second experiment determined the effects of regrowth interval (2 and 4 wk) and three stubble heights (2.5, 7.5, and 12.5 cm) under hay harvest management on the growth, nutritive value, and persistence of Mulato. When harvested every 2 wk at 2.5 cm, Mulato was less persistent but was greater in herbage accumulation and crude protein. Persistence of Mulato increased when harvested every 4 wk at a stubble height of 7.5 cm. It is concluded that Mulato is a feasible forage option for livestock producers in south Florida, but additional research assessing long-term persistence is needed.
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 Uduak Inyang.
Thesis: Thesis (M.S.)--University of Florida, 2009.
Local: Adviser: Vendramini, Joao M.B.
Local: Co-adviser: Sollenberger, Lynn E.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0024523:00001

Permanent Link: http://ufdc.ufl.edu/UFE0024523/00001

Material Information

Title: Management of Brachiaria Cultivar Mulato in South Florida
Physical Description: 1 online resource (82 p.)
Language: english
Creator: Inyang, Uduak
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2009

Subjects

Subjects / Keywords: accumulation, animal, average, bahiagrass, brachiaria, crude, cultivar, daily, defoliation, digestibility, gain, hectare, height, herbage, hybrid, interval, mass, mulato, nutritive, performance, persistence, protein, rates, regrowth, stocking, stubble, value, yield
Agronomy -- Dissertations, Academic -- UF
Genre: Agronomy thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Bahiagrass (Paspalum notatum Fl?gge) is the most planted forage in Florida covering approximately 2.5 million acres. Nonetheless, loss of stands due to mole crickets indicates a need for other grass species adapted to south Florida. Brachiariagrasses are the most widely grown warm-season forage in tropical America. Mulato is the first hybrid in the Brachiaria genus and results from crossing ruzigrass (Brachiaria ruziziensis clone 44-6) and palisadegrass (Brachiaria brizantha CIAT 6297). This new cultivar is known for its tolerance of prolonged drought and superior nutritive value, but its response to defoliation is unknown. Two field experiments were conducted to determine the yield, animal performance, and nutritive value of Mulato under varied management intensities and in comparison with bahiagrass. The experiments were conducted at the Range Cattle Research and Education Center, Ona, FL. The first experiment tested the effect of three stocking rates 4, 8, and 12 heifers (LW = 350 ? 21 kg) ha-1 on animal performance and herbage production of Mulato and bahiagrass pastures. There was an increase in herbage yield but a decrease in herbage allowance with increasing stocking rates. Mulato had greater herbage accumulation, crude protein, and digestibility than bahiagrass. Heifers grazing bahiagrass and Mulato pastures had lower daily gain at 12 heifers ha-1 but there was no difference between grasses at stocking rates of 4 and 8 heifers ha-1. Gain per hectare (GHA) and herbage accumulation (HMA) were greatest for Mulato pastures stocked at 8 heifers ha-1. The second experiment determined the effects of regrowth interval (2 and 4 wk) and three stubble heights (2.5, 7.5, and 12.5 cm) under hay harvest management on the growth, nutritive value, and persistence of Mulato. When harvested every 2 wk at 2.5 cm, Mulato was less persistent but was greater in herbage accumulation and crude protein. Persistence of Mulato increased when harvested every 4 wk at a stubble height of 7.5 cm. It is concluded that Mulato is a feasible forage option for livestock producers in south Florida, but additional research assessing long-term persistence is needed.
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 Uduak Inyang.
Thesis: Thesis (M.S.)--University of Florida, 2009.
Local: Adviser: Vendramini, Joao M.B.
Local: Co-adviser: Sollenberger, Lynn E.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2009
System ID: UFE0024523:00001


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1 MANAGEMENT OF BRACHIARIA C ULTIVAR MULATO IN SOUTH FLORIDA By INYANG UDUAK IME A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIR EMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2009

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2 2009 Inyang Uduak Ime

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3 To my father, Ime Sampson Inyang F or being an inspiration in pursuit of excellence and greatness all through the years

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4 ACKNOWLEDGMENTS The author would like to express her special thanks to Dr. Joa o Vendramini, chair of the supervisory committee. His relentless effort in planning and writing of the t hesis are sincerely appreciated. Extended thanks go to Dr. Lynn E. Sollenberger for his effort and assistan ce in making it possible for the smooth completion of the m asters program His guidance and motivation has undoubtedly shaped her perspective on an array of issues. Also thanks go to the rest of the advisory committee, Dr. Brent Sellers and Dr. Adegbola Ad esogan, for their w illingness to serve on the graduate committee and their thoughtful input in reviewing the thesis. Thanks are also due to Richard Fethiere of the Forage Evaluation Support Laboratory, for his assistance in sample analysis and Carly Althof f of the Range Cattle Research Unit for helping with field evaluations and data collection. Profound gratitude goes to Dr. Jerry Bennett, department chair, for recognizing the great potential for leadership and his recommendation for financial support towa rds the continuity of this graduate program Warm appreciation goes to the staff in Newell Hall (Kim Lottinville Cynthia Hight, Paula Cunningham, and Theresa Moore ) for their kind assistance. Great thanks go to Dr. John Arthington for funding my research in collaboration with the agronomy department (IFAS). The author wishes to express her appreciation to Dr. Ike Ezenwa, former advisor, for the opportunity to study in the United States. Gratitude goes to Mrs. Ebele Ezenwa ; Dr. Musibau Bam i kole ; Donna and C hucks Rowland; Drs. Joe and Ime Umana and also Dr. Charles Chekwa for their prayers, encouragement and support through the challenging times. Special thanks to Dr. Ademola Raji for his friendship and valuable support.

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5 Finally, great appreciation goes to m y parents, Ime Sampson Inyang and Afiong Inyang for instilling the right values and inspir ing the belief that it is possible to fulfill ones vision and aspiration s with an indomitable hustling spirit and an i ndefatigable attitude.

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6 TABLE OF CONTENTS pag e ACKNOWLEDGMENTS .................................................................................................................... 4 LIST OF TABLES ................................................................................................................................ 8 LIST OF FIGURES ............................................................................................................................ 10 ABSTRACT ........................................................................................................................................ 11 CHAPTER 1 INTRODUCTION ....................................................................................................................... 13 2 LITERATURE REVIEW ........................................................................................................... 16 Brachiaria: Origin, Introduction, and Economic Importance ................................................... 16 Center of Origin ................................................................................................................... 16 Introduction to the Ameri cas ............................................................................................... 16 Importance ............................................................................................................................ 17 The Important Brachiaria Species and Their Characteristics ................................................... 17 Brachiaria decumbens ......................................................................................................... 17 Brachiaria brizantha ........................................................................................................... 18 Brachiaria humidicola ........................................................................................................ 18 Brachiaria ruziziensis .......................................................................................................... 19 Description of the Mulato Hybrid .............................................................................................. 19 Breeding and Genetics ......................................................................................................... 19 Agronomic Characteristics and Nutritive Value ................................................................ 20 Bahiagrass .................................................................................................................................... 20 Origin .................................................................................................................................... 20 Agronomic Characteristics .................................................................................................. 21 Pensacola Bahiagrass ........................................................................................................... 21 Defoliation Fre quency and Intensity Effect ............................................................................... 22 Effect on Productivity .......................................................................................................... 23 Effect on Nutritive Value .................................................................................................... 25 Stocking Rates ............................................................................................................................. 26 Effect on Herbage Production and Nutritive Value ........................................................... 27 Effect on Animal Performance ........................................................................................... 28 3 EFFECT OF STOCKING RATES ON ANIMAL PERFORMANCE AND HERBAGE RESPONSES OF MULATO AND PENSACOLA BAHIAGRASS PASTURES ................. 31 Introduction ................................................................................................................................. 31 Materials and Methods ................................................................................................................ 33 Experimental Site ................................................................................................................. 33 Treatments and D esign ........................................................................................................ 33

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7 Pasture Management ............................................................................................................ 33 Plant and Animal Response Variables ............................................................................... 33 Statistical Analysis ............................................................................................................... 35 Results and Discussion ............................................................................................................... 36 Herbage Mass ....................................................................................................................... 36 Herbage Mass Accumulation Rate ..................................................................................... 38 Nutritive Value ..................................................................................................................... 39 Herbage Allowance ............................................................................................................. 43 Average Daily Gain ............................................................................................................. 45 Gain per Hectare .................................................................................................................. 48 Summary and Conclusions ......................................................................................................... 49 4 EFFECT OF STUBBLE HEIGHT AND HARVEST FREQUENCY ON FORAGE PRODUCTION AND NUTRITIVE VALUE OF BRACHIARIA CV. MULATO ................. 51 Introduction ................................................................................................................................. 51 Materials and Methods ................................................................................................................ 53 Experimental Site ................................................................................................................. 53 Treatments and Experimental Design ................................................................................ 54 Forage Measurements .......................................................................................................... 54 Statistical Analysis ............................................................................................................... 55 Results and Discussion ............................................................................................................... 55 Herbage Mass Accumulation .............................................................................................. 55 Forage Nutritive Value ........................................................................................................ 57 Summary and Conclusions .................................................................................................. 63 5 SUMMARY AND CONCLUSIONS ........................................................................................ 64 Mulato and Bahiagrass Grazing Study ...................................................................................... 65 Herbage Yield and Nutritive Value .................................................................................... 65 Animal Performance ............................................................................................................ 66 Defoliation Management Response ........................................................................................... 67 Herbage Mass Accumulation and Nutritive Value ............................................................ 67 Persistence ............................................................................................................................ 68 Implications of the Research ...................................................................................................... 68 APPENDIX : DATA TABLE ............................................................................................................. 69 LIST OF REFERENCES ................................................................................................................... 70 BIOGRAPHICAL SKETCH ............................................................................................................. 82

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8 LIST OF TABLES Table page 3 1 Stocking rate x species x month interaction effects on herbage mass of bahiagrass and Mulato past ures. .............................................................................................................. 36 3 2 Year x month interaction effects on herbage mass of bahiagrass and Mulato pastures. ... 37 3 3 Stocking rate x month in teraction effects on herbage mass accumulation rate of bahiagrass and Mulato pastures. ............................................................................................ 3 8 3 4 Year x species x month interaction effects on herbage mass accumulation rate of bahiagrass and Mul ato pastures. ............................................................................................ 39 3 5 Stocking rate x month interaction effects on crude protein of bahiagrass and Mulato pastures. .................................................................................................................................. 40 3 6 Stocki ng rate x month interaction effects on in vitro digestible organic matter of bahiagrass and Mulato pastures. ............................................................................................ 41 3 7 Year x species x month interaction effect on crude protein concentration of bahiagrass and Mulato pastures. ............................................................................................ 42 3 8 Year x species x month interaction effect on in vitro digestible organic matter concentration of bahiagrass and Mulato pastures. ............................................................... 43 3 9 Stocking rate x species x month interaction effect on herbage allowance of bahiagrass and Mulato pastures. ............................................................................................ 44 3 10 Year x month interaction effec ts on herbage allowance of bahiagrass and Mulato pastures. .................................................................................................................................. 45 3 11 Year x month interaction effects on ADG of Mulato and bahiagrass pastures. ................. 47 3 12 Stocking rate x species x month interaction effects on ADG of Mulato and bahiagrass pastures. ................................................................................................................ 48 4 1 Regrowth interval x month interaction effects on herbage mass of Mula to forage. .......... 56 4 2 Regrowth interval x stubble height interaction effects on crude protein of Mulato forage ...................................................................................................................................... 57 4 3 Regrowth inter val x month interaction effects on crude protein of Mulato forage. .......... 58 4 4 Stubble height x month interaction effects on crude protein concentration of Mulato forage. ..................................................................................................................................... 59

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9 4 5 Regrowth interval x month interaction effects on in vitro digestible dry matter concentration of Mulato forage. ............................................................................................ 60 4 6 Stubble height x month inter action effects on in vitro digestible dry matter concentration of Mulato forage. ............................................................................................ 61 4 7 Regrowth interval x stubble height interaction effects on percentage cover of Mulato. ... 62 A 1 Weather data for Years 2007 and 2008 in Ona, FL. ............................................................ 69

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10 LIST OF FIGURES Figure page 3 1 Nonlinear correlation between HA and ADG for Mulato and bahiagrass pastures stocked at 4, 8, and 12 heifers ha1. ....................................................................................... 46 3 2 Average daily gain of heifers Mulato and bahiagrass pastures stocked at 4, 8, and 12 heifers ha1. ............................................................................................................................. 46 3 3 Gain per ha of heifers grazing Mulato and bahiagrass pastures stocked at 4, 8, and 12 heifers ha 1. ............................................................................................................................ 49

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11 Abstract of Thesis Presente d to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science MANAGEMENT OF BRACHIARIA C ULTIVAR MULATO IN SOUTH FLORIDA By Inyang Uduak Ime May 2009 Chair: Joao Vendr amini Cochair: Lynn Sollenberger Major: Agronomy Bahiagrass ( Paspalum notatum Flgge) is the most planted forage in Florida covering approximately 2.5 million acres. Nonetheless, loss of stands due to mole crickets indicate s a need for other grass species adapted to s outh Florida. Brachiariagrasses are the most widely grown warm -season forage in tropical America. Mulato is the first hybrid in the Brachiaria genus and results from crossing ruzigrass (Brachiaria ruziziensis clone 446) and palisadegrass ( Bra chiaria brizantha CIAT 6297). This new cultivar is known for its tolerance of prolonged drought and superior nutritive value, but its response to defoliation is unknown. Two field experiments were conducted to determine the yield, animal performance, and n utritive value of Mulato under varied management intensities and in comparison with bahiagrass. The experiment s w ere conducted at the Range Cattle Research and Education Center, Ona, FL. The first experiment tested the effect of three stocking rates [4, 8, and 12 heifers (LW = 350 21 kg) ha1] on animal performance and herbage production of Mulato and bahiagrass pastures. There was a n increase in herbage yield but a decrease in herbage allowance with increasing stocking rates. Mulato had greater herbage a ccumulation, crude protein and digestibility than bahiagrass. Heifers grazing bahiagrass and Mulato pastures had low er daily gain at 12 heifers ha1 but there was no difference between grasses at stocking rates of 4 and 8 heifers ha1. Gain per hectare (G HA) and

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12 herbage accumulation (HMA) w ere greatest for Mulato pastures stocked at 8 heifers ha1. The second experiment determined the effects of regrowth interval (2 and 4 wk) and three stubble heights (2.5, 7.5, and 12.5 cm ) under hay harvest management on the growth, nutritive value, and persistence of Mulato When harvested every 2 wk at 2.5 cm, Mulato was less persistent but was greater in herbage accumulation and crude protein. Persistence of Mulato increased when harvested every 4 wk at a stubble heigh t of 7.5 cm. It is concluded that Mulato is a feasible forage option for livestock producers in south Florida but additional research assessing long term persistence is needed

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13 CHAPTER 1 INTRODUCTION Florida is the 13th state in the USA in number of bee f cows with approximately one million head (USDA Census of Agriculture, 2002). Beef cattle produced cash receipts of 293 million US dollars in 1998 (Hodges et al., 2004) which increased to 4 30 m illion US dollars in 2007 In Florida, most beef cattle operations rely on warm -season grasses as the primary source of nutrients Bahiagrass is an essential resource to the beef industry in Florida. It is the most widely planted warm -season grass in the state, covering approximately one million hectares. Of this ar ea, 90% is grazed by beef cattle (Chambliss, 2000). Bahiagrass is relatively tolerant to drought and low fertility soils (Prates et al., 1975). This makes bahiagrass well adapted to the range of environmental conditions in Florida. The most widely distributed bahiagrass cultivar is Pensacola and it is known for its relatively high yields and moderate animal performance (Chambliss, 2000). Since 1996 through 2000, more than 150,000 h a of bahiagrass pastures were damaged by mole cricket (Scapteriscus spp.) in Florida (Adjei et al. 2001). Damage to bahiagrass pastures by armyworms ( Pseudaletia unipuncta), grasshoppers ( Melanoplus differentialis ), and loss of stands due to mole crickets stimulated a search for other grasses adapted to the S outh Florida enviro nment Brachiaria species are well adapted to low -fertility acid soils of the tropics because they are tolerant of high Al low P, and low Ca concentrations (Rao et al. 1995; Rao et al., 1996; Wenzl et al., 2002). Brachiaria cv. Mulato shares many of the desirable characteristics of bahiagrass, establishes from seed, tolerates low fertility and requires minimal pest control inputs, and is persistent when defoliated Although, Mulato d oes not tolerate variations in edaphic and climatic conditions as well a s bahiagrass does, it is adapted to infertile soils of C entral and S outh

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14 America ( Argel et al., 2005) Mulato is known for its tolerance of prolonged drought and recovery after sporadic frost. Some Brachiaria cultivars are being offered for sale in S outh Fl orida but little scientific information is available on these new entries. Stocking rate is the relationship between the number of animals and the area of pasture to which they are assigned over an extended period of time. Increasing stocking rate implies increasing animal s consum ing available herbage a given area of grassland but this often leads to a decrease in individual animal production. The effect of increasing management intensity on plant persistence and animal performance must be determined b efo re recommending plants for use by producers The s tocking rate and method adopted plays an important role in affecting cost of production, and utilizing available herbage (Matches, 1992). It is im p o rt a nt to understand the effects of defoliation frequency and intensity on plant persistence, productivity and nutritive value in order to develop harvest management recommendations (Chaparro et al. 1995, 1996). Frequent removal of forage may decrease non structural carbohydrate reserves, decreasing the plant s ability to produce DM; however, as interval between defoliation increases, CP and IV D OM may decrease. Frequent defoliation prevents plants from reaching maturity, thus increasing the proportion of young, lush herbage. Defoliation by grazing or clipping to a short stubble height may reduce persistence and cause encroachment by other grasses (New m an et al., 2002). Th e objective of this research was to assess the adaptation of Mulato to S outh Florida and develop basic management practices for this newly intr oduced warm -season grass cultivar. The research was divided into two experiments. The first experiment evaluated animal performance and forage response of bahiagrass and Mulato pastures to three stocking rates Animal performance was measured a s average da ily gain (ADG) and gain per hectare (GHA) of beef

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15 heifers grazing Mulato and bahiagrass pastures Forage responses included nutritive value, herbage mass (HM) herbage allowance (HA) and herbage mass accumulation (HMA) Results from this study will provid e information to producers consider ing the use of Mulato as an alternative warm -season grass species for bahiagrass. In addition, information provided by this study will allow producers to make better decisions regarding stocking rates for Mulato and bahia grass pastures and ultimately increase the profitability of their agriculture enterprise. The second experiment evaluated forage responses of two regrowth intervals and three stubble heights o f Mulato Forage responses measured include d nutritive value, HM A and Mulato percent cover over time These data will allow conclusions to be drawn about the harvest management practice s of Mulato hay fields that favor herbage production and persistence Data from bo th experiments will help producers understand manage ment strategies to optimize the utilization of Mulato as a complement or alternative to bahiagrass in S outh Florida.

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16 CHAPTER 2 LITERATURE REVIEW Brachiaria: O rigin, Introduction, and Economic Importance Cente r of Origin Brachiaria species are native f rom Africa. The commercially exploited brachiariagrasses species are: Brachiaria brizantha (palisadegrass); B. ruziziensis (ruzigrass); B. decumbens (signalgrass); and B. humidicola (koroniviagrass) (Miles, 2004). Apart from palisadegrass which is found t hroughout tropical Africa, the other three Brachiaria species are found around the latitude of the Equator in eastern Africa (Keller Grein et al. 1996). Brachiaria belongs to a small group of genera that includes Urochloa, Eriochloa, and Panicum All have the PEP CK (phosphoenol pyruvate carboxykinase) type of C4 photosynthetic pathway (Clayton and Renvoize, 1986) and, although they have been recognized for over 100 yr, the precise separation of these genera is still in doubt. Urochloa is scarcely separabl e from Brachiaria differing in little but the orientation of the spikelet (Renvoize et al., 1996). Some Brachiaria are difficult to separate from Panicum based on the inflorescence characteristics. A phylogenetic analysis based on nucleotide base sequenc e polymorphisms of the internal transcribed DNA did not separate Brachiaria from Urochloa. It was concluded that neither genus is monophyletic (Torres Gonzalez, 1998). Introduction to the Americas The e xisting Brachiaria cultivars were direct selections o f germplasm collected from Africa (Kenya, Ethiopia, Uganda, Tanzania, Zimbabwe, Rwanda, and Burundi). Brachiaria was first introduced in tropical Australia in the early 1960s and subsequently in tropical South America, beginning with Brazil in early 1970s (Parsons, 1972; Sendulsky, 1978). The Brachiaria

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17 cultivars were developed by several institutions and released in one or more tropical American countries Brazil, Colombia, Mexico, Cuba, etc. (Miles and Lapointe, 1992). Importance Brachiariagrasses are the most widely grown forages in tropical America, occupying over 80 million ha (Boddey et al., 2004). Brachiaria species are extensively used as pasture grasses. They are not commonly harvested and stored, although hay is sometimes made from signalgrass and other species (Boonman, 1993; Stur et al., 1996). They are planted primarily for fattening and breeding beef cattle, but are not pop ular for dairying because of their relatively low forage quality ( Stur et al., 1996). They are used often in rotation w ith annual crops such as rice [Oryza sativa L. (Sanz et al., 1999)]. Brachiaria species are popular among producers because they show rapid regrowth and good persistence under heavy or frequent defoliation (Rika et al ., 1991). The Important Brachiaria Spec ies and Their Characteristics Brachiaria decumbens Signalgrass is a vigorous stoloniferous perennial, established by seed, either broadcast or planted in rows (Gil et al., 1991). Once established, this species tolerates temporarily waterlogged soils, although it grows better on well drained ones. According to the Centro International de Agricultura Tropicale (CIAT), s ignalgrass can tolerate up to 6 mo of drought (CIAT, 1998). It is highly susceptible to spittlebug but tolerates leaf -eating insects. T he t emp erature for optimal growth of signalgrass is 30 to 35C. It is readily frosted. Values of in vitro dry matter digestibility (IVDMD) in signalgrass have ranged from 60 0 to 70 0 g kg1 in immature forage, and from 500 to 60 0 g kg1 in mature forage greater t han the average (55 0 g kg1) for tropical forage grasses (Lascano and Euclides, 1996).

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18 Brachiaria brizantha Palisadegrass is a highly productive grass that is propagated by seed and vegetatively by clumps and stems. It can spread slowly by seed as the seed ages to break its dormancy (Ellis, 1988). It requires more fertile and better drained soils than other species of Brachiaria and has a higher tolerance to drought. Palisadegrass persists under severe grazing and frequent harvesting (Granier and Lahore, 19 66; Urio et al., 1988). It has the ability to spread and suppress weeds and is highly resistant to rust, leaf cutting ants (Atta cephalotes ), and spittlebugs (Deois sp. and Notozulia entreriana), but is highly susceptible to Rhizoctonia foliar blight (CIAT 1998; Urriola et al., 1988). Rhizoctonia foliar blight is a disease that can be very destructive when environmental conditions are particularly conducive (high relative humidity, dense foliar growth, high nitrogen fertilization, and extended wet periods ). Palisadegrass is one of the most cultivated forage grasses in Central Brazil, due mainly to spittlebug resistance and high yield potential. In the Zona da Mata of the state of Pernambuco, n ortheastern Brazil, the total herbage accumulation in palisadegra ss pastures can reach 28 Mg dry matter ( DM ) ha1 during the grazing season (from September 1998 through April 1999, Santos et al., 2003). About 10.5 million ha (21% of total improved grassland areas) are cultivated with palisadegrass in Central Brazil, sup porting 56 million head of cattle ( Bos sp Vilela et al. 2004). Released by the Empresa Brasileira de Pesquisa Agropecuaria (EMBRAPA ) in 1984 Marandu palisadegrass currently ranks first in the Brazilian forage seed market: 44% of the total amount of s eed commercialized (Valle et al., 2004). Brachiaria humidicola Koroniviagrass is a s toloniferous perennial grass. Though established by seeds, farmers in the humid tropics favor vegetative propagation using mature stolons. It tolerates waterlogged or inte rmittently flooded soils such as chromic Vertisols (Amaya Hernandez and Carmona Munoz,

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19 1988). Although it can withstand dry periods (Urriola et al., 1988), DM yield was reduced by 40% (Tergas, 1981). Koroniviagrass has high DM yield with IVD D M ranging from 48 0 to 62 0 g kg1, and CP from 50 to 12 0 g kg1 (Hoyos and Lascano, 1985; Munoz, 1985), although N fertilization improves these parameters (Botrel et al., 1990). Koroniviagrass is highly resistant to leaf cutting ants and tolerates but is not truly res istant to spittlebugs (Lapointe and Miles, 1992). Brachiaria ruziziensis Ruzigrass has hi gh nutritive value and is propagated by seeds. It is fast growing early in the wet season and compatible with legumes. It has high seed production potential but low c ompetitiveness with weeds. It requires more fertile and well drained soils than palisadegrass It has good drought tolerance but is highly susceptible to spittlebugs. When harvested every 6 wk, ruzigrass had a CP of 14 0 g kg1 and IVDMD from 670 to 71 0 g kg1 (Vallejos, 1988; do Valle et al. 1988). Description of the Mulato Hybrid Breeding and Genetics A hybridization program was initiated at the CIAT, conducted in collaboration with EMBRAPA with the objective to produce improved brachiariagrass cultivars with outstanding agronomic characteristics, greater range of adaptation, higher biomass production and nutritional quality, and resistance to Rhizoctonia and multiple spittle bug species This effort generated Mulato, an apomictic hybrid (CIAT, 2000) whic h is the first commercial hybrid in the Brachiaria genus. Mulato result ed from crossing Brachiaria ruziziensis clone 44 6 X Brachiaria brizantha CIAT 6297, and this was carried out in 1988 (CIAT, 2001). A series of agronomic tests in Mexi co, Colombia, and Central America has proved Mulato to be high in vigor and with good production potential (Miles, 1999).

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20 Agronomic Characteristics and Nutritive Value Mulato is a semi -erect perennial apomictic grass that can grow up to 1.0 m tall. It is established by se ed, although it could be propagated vegetatively by rooted stem stocks. It produces vigorous cylindrical stems, some with a semi -prostrate habit, capable of rooting at the nodes when they come in close contact with soil. Mulato has lanceolate and highly pu bescent leaves of 40 to 60 cm in length and 2.5 to 3.5 cm width (Guiot and Melendez, 2003). Mulato grows well in humid tropical areas with high rainfall and short dry periods, and in sub-humid conditions with 5 to 6 dry months and annual rainfall of 700 mm It has been reported by Argel et al., 2005 that Mulato grows well in subtropical conditions where periodic frost occurs such as southern Florida in the US A It grows in acid to alkaline soils (pH 4.2 8.0), but it requires medium to high fertility and g ood drainage Mulato is drought tolerant and has the capacity to regrow again during critical times of the year. It has CP concentration fluctuating between 9 0 to 170 g kg1 and digestibility of 550 to 62 0 g kg1 (CIAT, 2005; CIAT, 2006). It produces 25% m ore DM yield than palisadegrass and signalgrass increasing animal productivity from 1 to 2 kg milk cow1 d1 over that achieved on palisadegrass cv. Marandu or palisadegrass cv. Toledo (Peters et al., 2003). Bahiagrass Origin Scott (1920), cited by Gate s et al. (2004), reported that bahiagrass was first introduced into the USA by the Bureau of Plant Industry and grown by the Florida Agricultural Experiment Station in 1913. After its introduction into Florida, it soon escaped from cultivation and rapidly became naturalized throughout Florida Bahiagrass is particularly tolerant of poor soil drainage, close continuous grazing, and marginal fertility. Currently, bahiagrass is widespread throughout

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21 the southern USA and Central and South America (Chambliss a nd Adjei, 2006). It is used extensively as pasture and utility turf on highway right s -of -way (Gates et al., 2004). Agronomic Characteristics Bahiagrass is a low -growing perennial spreading by short, stout rhizomes and can grow up to 30 cm tall. It is prim arily established by seed. It produces vigorous leaf growth and has a prostrate growth habit It has many large, fibrous roots and form s dense, tough sods, even on drought prone sandy soils. It has pubescent basal leaves, with a purple glabrous sheath. The culms (stems) of bahiagrass are ascending, usually ranging from 20 to 75 -cm tall, and the dark green leaves are 4 to 10 -mm wide and linear -elongate in shape. The leaf blades are typically 6 to 25 cm long and the leaf sheaths are generally 4 to 20 cm lon g Bahiagrass grows well in humid tropical areas with high rainfall and short dry periods but requires a minimum annual rainfall of 750 mm. It grows in acid soils (pH 5.0 6.5). Bahiagrass is drought tolerant but it produces less biomass during critical times of the year, particularly in winter. It has CP concentration fluctuating between 7 0 to 10 0 g kg1 and a digestibility from 49 0 to 51 0 g kg1. Bahiagrass is one of the most important cultivated grasses in Florida and the southern part of the Gulf Stat es of the USA. Pensacola B ahiagrass Pensacola bahiagrass belongs to the botanical variety Paspalum notatum var. saurae Parodi. It is a sod -forming perennial grass of tropical origin which concentrates its forage production near the soil surface. It is t aller, spreads faster, has longer narrower leaves, smaller spikelet s and can have more racemes per inflorescence than common bahiagrass (Gates et al., 2004). Pensacola bahiagrass was introduced into North America in 1936 (Burton, 1967) its widespread pro liferation throughout the lower southeastern USA demonstrates excellent adaptation by this species to regional environmental conditions. It is fairly frost tolerant and

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22 growth starts early in the spring. In Florida, DM yields of Pensacola bahiagrass during the growing season ranged from 3000 to 4000 kg ha1 (Blue, 1970). Nonetheless, most production occurs during spring and summer (April September). Plant response to short days appears to account for at least some of the seasonality of production. Mislevy et al. (2001) reported a 167% increase in total cool -season herbage accumulation of Pensacola bahiagrass when day length was extended from 10.4 to 15 h. Defoliation Frequency and Intensity Effect The principal function of green plants is to intercept eno ugh solar radiation in the foliage to guarantee the energy supply for their growth and development (Hodgson, 1990). Plants in pastures that are continuously stocked at a high stocking rate will be defoliated frequently, so there is little shading of leaves in the lower part of the canopy due to constant leaf removal. Forage plants must have adaptation mechanisms to survive frequent and severe grazing or harvests. The immediate effect of a harvest is the reductio n of leaf area, and therefore, the quantity of intercepted light, carbohydrate reserves, and root growth (Richards, 1993). The ability to rapidly re -establish the photosynthetic capacity of the canopy after defoliation is an important characteristic of defoliation -tolerant plants, and the presence of active shoot meristems allows for rapid leaf expansion from existing cells (Mott and Lucas 19 5 2). Swards sown to warm or cool -season perennial forages often change with time into mixtures that vary in botanical composition, herbage productivity, and nutr itive value. Cool -season swards clipped or grazed intensively can be invaded by warm -season species, such as crabgrass ( Digitaria spp.), and warm -season swards can be invaded by a number of cool -season species adapted to a site, especially in spring and la te summer. When established brachiariagrass pastures are defoliated, the regrowth curve is roughly sigmoid. After an initial lag in recovery of growth, the exponential growth phase begins but its

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23 extent and duration depends on the intensity of grazing and the species (Lascano and Euclides, 1996). The accumulation of DM in forage plants ensues from complex interactions of genetic attributes environment and their effect s on physiological processes and the morphologic characteristics of the plants (Da Silva and Quarry, 1997). Different grazing frequencies generate changes in the structure of the canopy, modifying the l ight environment and resulting in canopies with different photosynthetic potentials. The photosynthetic rate of individual le aves is reduced wh en there is dim inished grazing frequency. This compromis es the photosynthetic potential of the canopy while also generating a delay in regrowth. A lesser frequency of defoliation generates competition for light and reduces values of foliar photosynthesis a nd canopy. Braga et al (2006 ) recommended optimum management practices for Xaras palisadegrass to include grazing intervals shorter than 28 d, so that higher photosynthetic rates are achieved during the regrowth period. Effect on Productivity The influ ence of grazing frequency on ruzigrass palisadegrass and signalgrass fertilized with 170 kg ha1 N and clipped to a 7.5 -cm stubble height was found to be the opposite of effects observed for most grasses, showing highest persistence when grazing frequenc y wa s 2 or 3 wk. Delaying grazin g frequency of these three Brachiaria grasses to 5 or 7 weeks may allow plants to develop an oversupply of forage, which shades the stem bases and regenerative buds (Mislevy et al., 1996). The decrease in stand persistence of signalgrass and palisadegrass at each harvest frequency indicates that these grasses may not be adapted to clipping to a 7.5-cm stubble height. Koroniviagrass show ed the highest DM yield at 7 -wk regrowth interval s (Mislevy et al., 2002). Palisadegrass can be heavily grazed if regularly fertilized with N (Sivalingam, 1964). If grown with a legume, the grazing system must favor the legume, and adequ ate P must be provid ed. In Sri Lanka, Sivalingam (1964) recommended a cutting interval of 30 d when

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24 palisade grass was fertilized with N at 0, 45, 132, and 396 kg ha1. Cumulative DM yield of palisadegrass increased with increasing N rates from 0 to 400 kg ha1 when cut every 40 d (Mtengeti and Lwoga, 1989, unpublished report). Mulato had greater DM yield when cut every 28 (4.0 Mg ha1) compared to 21 (2.6 Mg ha1) and 35 d (4.6 Mg ha1; Hidalgo, 2004). Cuomo et al. (1996) compared three grazing frequencies, 20, 30, and 40 d, of bahiagrass across two growing seasons. At these frequencies, total forage DM product ion was 10.6, 11.8, and 12.3 Mg ha1, respectively. Herbage CP was significantly greater at 20 -d grazing frequency (124 g kg1), but it was equal for the 30 and 40-d intervals (110 g kg1). In vitro true digestibility did not significantly change across gr azing frequencies (590 g kg1). Stanley (1994) compared bahiagrass at harvest intervals of 1, 2, 4, 8, and 16 wk, with N fertilization rate of 336 kg ha1. Forage DM production was highest for the 8 -wk interval (18.9 Mg ha1). Relative production for the remaining harvest intervals (with DM productions of the 8 wk treatment assigned a value of 1.00) were 0.36, 0.53, 0.81, and 0.75 for the 1, 2, 4, and 16-wk treatments, respectively; illustrating an increase in forage production as harvest interval increase s to 8 -wk, but no further increase with delayed harvest Beaty et al. (1970) evaluated bahiagrass across six harvest frequencies, 1, 2, 3, 4, 5, and 6 wk. At these frequencies, average DM production for the 2 yr study were 3.5, 3.4, 3.0, 2.7, 3.8, and 2.6 Mg ha1, respectively, showing little effect of clipping frequency. Without fertilization, as much as 67% of total Pensacola herbage mass was found in the bottom layers (0 2.5 cm) of the canopy. This indicated that close defoliation may improve forage nut ritive value by reducing the amount of dead material that accumulates under lax defoliation methods. Gates et al. (1999) compared 2 4 -, and 8 -wk -old regrowth of Pensacola, Tifton 9 and RRPS C ycle 14. D epletion of reserves available for growth was evident in the reduction of

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25 etiolated spring growth of bahiagrass plots harvested biweekly (74 g DM m2) for 2 yr in comparison with 4 -wk (81g DM m2) or 8 -wk (105 g DM m2) harvest intervals. Effect on Nutritive Value According to Gates et al. (2001), Pensac ola bahiagrass exceeded Tifton 9 in CP concentrations on five different harvest dates. This was consistent with previous findings of Mislevy et al. (1990), who demonstrated that CP concentrations were higher in Pensacola than in Tifton 9 bahiagrass The CP concentration of all bahiagrass cultivars at 2 to 5w k grazing frequencies was more than adequate to meet the requirements of lactating beef cows (90 to 100 g kg1) and lactating heifers (100 to 120 g kg1, National Research Council, 1984). However, whe n grazing frequency ( GF ) was delayed to 7 w k forage CP concentration of all grasses was just adequate to meet requirements of lactating beef cows. In Araatuba, So Paulo Vendramini et al. (1999) evaluated Tifton 9 bahiagrass harvested at six regrowth i ntervals (20, 27, 34, 41, 48, and 55 d after staging). Plots received 60 kg ha1 of N for the period of January to March 1997. Dry matter yield ranged from 188 to 593 g m2. Crude protein was found to decrease linearly from 121 to 69 g kg1as regrowth inte rval increased. In a 3 -yr clipping study, Mislevy et al. (2005) reported greatest bahiagrass forage CP and IV D OM in April (157 and 534 g kg1respectively), October (157 and 542 g kg1, respectively), and December (177 and 587 g kg1, respectively), while lowest CP and IV D OM were always found in June (113 and 467 g kg1, respectively) and August (122 and 482 g kg1, respectively). Stewart et al. (2007) reported that Pensacola bahiagrass herbage CP and IV D OM in continuously stocked pastures generally decreas ed from May through August. Hirata (1993) reported greatest annual IVDDM of Pensacola when harvested at 2 -cm stubble height (570 g kg1) and lowest IVDDM at 22 -cm stubble (460 g kg1). This author also

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26 reported IV DDM was greater in the spring (580 g kg1 a t 2 -cm stubble and 540 g kg1at 22 -cm stubble) than autumn (530 g kg1 at 2 -cm stubble and 430 g kg1at 22 cm stubble). Haddad et al. (1999) evaluated the production characteristics and nutritive value of Pensacola bahiagrass at six regrowth intervals (20, 35, 50, 65, 80 and 95 d after staging) from December 1987 to March 1988 in Brazil They found DM production increased quadratically (from 161 to 418 g m2) while IV DDM decreased quadratically (from 678 to 373 g kg1) with increased regrowth intervals Had dad et al (1999) reported a decline in nutritive value of Pensacola bahiagrass from 20 to 50 d of regrowth after cutting [678 to 448 g kg1 (IVDDM) and 145 to 97 g kg1 (CP)] Results showed that the recommended harvest should be performed approximately a t 30 d interval s in order to balance forage production and nutritive value. The CP and IV D OM of signalgrass, ruzigrass, palisadegrass, and koronviagrass fertilized with 170 kg ha1 N and clipped to a 7.5 -cm stubble height decreased after 5 w k. Regardless of the grazing frequency koronviagrass was the lowest in IVDOM (Mislevy et al., 1996; Mislevy et al., 2003). Crude protein concentration of palisadegrass declined with longer cutting interval s but increased from 69 to 129 g kg1 when N was increased from 0 to 400 kg ha1. According to Mislevy et al. (1996), koronviagrass holds a distinct advantage over bahiagrass in digestibility. K oronviagrass had 77 (June July) and 80 g kg1 (August September) greater IVDOM than Pensacola bahiagrass when grazed at a 2 1 -d frequency. In a clipping trial, average IV D OM of koronviagrass from April to September was 120 g kg 1 higher than Pensacola (Mislevy and Everett, 1981). K oronviagrass and bahiagrass contained CP of 119 and 139 g kg1 and IVDOM of 550 and 499 g kg1, re spectively e arly in June Stocking Rates Stocking rate is a fundamental variable for management that affects vegetation, livestock, and economic responses (Gillen and McCollum, 1992; McCollum et al., 1999). When stocking

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27 rate is imposed across a relative ly wide range, it has a profound effect on the forage especially forage mass and subsequent animal performance (Burns et al., 1989). It h as been established that stocking rate affects ADG (Guerrero et al., 1984; Bransby et al., 1988; Gillen et al., 1992). At l ow stocking rates, ADG is maximized, but a heavier stocking rate maximizes gain per hectare. Maximum net return per hectare usually occurs between 55 to 60% of the stocking rate that produces maximum gain per hectare (Hart et al., 1988). Bransby et al (1988) proposed that the function describing the relationship between stocking rate and animal performance is unique for each forage type. Effect on Herbage Production and Nutritive Value Stewart et al. (200 7 ) evaluated the effects of three management in tensity treatments low (40 kg N ha1 yr1, 1. 4 AU ha1 target SR), moderate (120 kg N ha1 yr1, 2. 8 AU ha1 target SR), and high (360 kg N ha1 yr1, 4.2 AU ha1 target SR) on beef heifer performance and bahiagrass production and nutritive value. Herbage accumulation (41 vs. 17 kg ha1 d1), CP (140 vs. 99 g kg1), and IVDOM (505 vs. 459 g kg1) of bahiagrass pastures were greater for High than L ow intensity Herbage allowance was 1.4 kg DM kg1 liveweight ( LW ) for h igh compared to 4 .8 kg DM kg 1 LW for l o w management intensity. Utley et al. (1974) reported greater animal performance on continuously stocked Coastcross 1 -bermudagrass (0.68 kg d1) than on Pensacola bahiagrass and Coastal bermudagrass (average 0.46 kg d1), when pastures were grazed for 4 yr and fertilized with 168 kg N ha1 yr1 in Tifton, GA. Sollenberger et al. (1988) showed that total season ADG of bahiagrass seldom exceeds 0.5 kg d1. They showed ADG of 0.38 and 0.33 kg d1, and carrying capacities of 5.2 and 5.4 steers (320 kg ha1) fo r Pensacola bahiagrass and Floralta limpograss [Hemarthria altissima (Poir.) Stapf and C.E. Hubbard] respectively. Pastures were continuously stocked for 2 yr in Florida.

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28 Gain per hectare was 370 and 344 kg for bahiagrass and limpograss respectively, wh en pastures received N fertilization of 190 kg ha1 each year. However, this was because stocking rate was higher on limpograss than on bahiagrass. Dubeux et al., ( 2006) conducted a 3 yr study to evaluate the effects of a wide range of management intensities on patterns of herbage and soil nutrient responses in Pensacola bahiagrass pastures. The three management intensities were: l ow (40 kg N ha1 yr1 and 1.4 AU ha1 stocking rate [SR] ), m oderate (120 kg N ha1 yr1 and 2.8 AU ha1 SR), and h igh (360 kg N ha1 yr1 and 4.2 AU ha1 SR). It was reported that herbage N was greatest at the h igh SR, within the range of 20 to 23.5 g kg 1 DM but it showed lower values for l ow SR within the range of 14 to 15.7 g kg1 DM. At h igh SR, IV D OM varied from 436 to 558 g kg1 but showed lower values for l ow SR of 419 to 496 g kg1. In Florida, herbage mass accumulation (HMA) of Tifton 85 bermudagrass at SR 11.1, 11.2, and 13.7 AU ha1 varied throughout the grazing season ranging from 45 to 121 kg DM ha1 d1 in 2003 and from 56 to 133 kg DM ha1 d1 in 2004 (Vendramini et al, 2007). Effect on Animal Performance Stocking rate of pastures is a key determinant of pasture and animal production, and for most responses has a much greater impact than N fertilizer rate Stewart et al. (200 7 ) studied the effects of three management intensities (include stocking rates and N fertilization levels) on performance of beef heifers grazing bahiagrass pastures in Florida. Averages across 4 yr of grazing continuously stocked bahiagrass showed an ADG and gain per hectare of 0.34 kg and 101 kg ha1, and 0.28 kg and 252 kg ha1 for Low and High, respectively. Stewart et al. (2007) reported greater heifer ADG (0.34 and 0.28 kg d1, respectively) for Pensacola bahiagrass under low intensity man agement (40 kg N ha1 yr1, 1.4 AU ha1 SR) than high intensity (360 kg N ha1 yr1, 4.2 AU ha1 SR), but gain per hectare increased from low to high intensity (101 to 252 kg

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29 ha1). Greater CP (140 vs. 99 g kg1 ) and IV D OM (505 vs. 459 g kg1 ) were observ ed at high than at low intensity management for bahiagrass. Animut et al. (2005) studied s tocking rates of 4, 6, and 8 animals per 0.4-ha pasture, with equal numbers of sheep and goats stocked rotational ly. Average daily gain tended to decrease linearly a s SR increased (61, 51, and 47 g d1), and gain per hectare increased linearly to 610, 759, and 933 g d1 for SR4, SR6, and SR8, respectively. Hernndez Garay et al. (2004) reported a quadratic decrease in ADG of weanling bulls grazing stargrass (Cynodon nlemfuensis Vanderyst ) pastures as stocking rate increased from 2.5 to 7.5 bulls ha1. Average daily gain decreased from 0.70 to 0.26 kg d1 in Year 1 and 0.65 to 0.35 kg d1 in Year 2 as stocking rate increased from 2.5 to 7.5 head ha1. Salazar -Diaz (19 77) reported a relationship of 1.05, 1.02, and 1.36 kg of LW per kg N applied, with low, medium, and high SR, respectively for digitgrass ( Digitaria eriantha Steud.) pastures. Increased SR increases consumption of herbage ha1, but there is a shift in use of consumed energy from maximum daily animal growth at low SR, toward maintenance of the animals at moderate to high SR. Adjei et al. (1980) conducted grazing trials to study the effects of three SR (7.5, low; 10, medium; and 15 steers ha1, high) on fora ge yield, nutritive value, and utilization and animal performance of three stargrasses: UF 5 and McCaleb (Cynodon aethiopicus Clayton and Harlan) and UF 4 (Cynodon nlemfuensis Vanderyst var. nlemfuensis ). Additionally, the medium SR was imposed on Transvala digitgrass ( Digitaria eriantha Ste ud ) and Pensacola bahiagrass The average annual DM yields of stargrasses at low, medium, and high SR and of digitgrass and bahiagass at medium SR were 17.0, 18.3, 20.1, 15.0, and 10.0 Mg ha1, respectively. Th e ADG and gain per hectare at the medium SR on stargrass, digitgrass, and

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30 bahiagrass averaged 0.35, 0.28, 0.22, kg d1, and 580, 461, and 396 kg ha1, respectively. During 168d experimental period in Florida, ADG of yearling beef steers grazing stargrass (average of three cultivars and 2 yr) was 0.47, 0.38, and 0.21 kg d1 for SR treatments of 7.5, 10, and 15 steers ha1 (initial weight of 230 250 kg). Gunter et al. (2005) reported that the ADG of beef steers was decreased by increasing the stocking rate on dallisgrass pasture fertilized with 112 kg N ha1, Stocking rates of 3.7, 6.2, 8.6 and 11.1 steers ha1 resulted in an ADG of 0.63, 0.61, 0.51 and 0.34 kg d1, respectively. Increasing stocking rate resulted in quadratic decreases in the total BW gain per steer. Aiken et al (2006) studied the influence of stocking rate and steroidal implants on growth rate of steers grazing pasture of tall fescue ( Festuca arundinacea Schreb. ). Forage mass declined linearl y from 4000 to 3600 kg of DM ha1as stocking r ate increased. There was no ADG response to stocking rate but there was a linear decrease in gain per hectare as stocking rate increased. Trends in gain per hectare showed that 6.0 steer s ha1, with or without implantation, provided approximately a 75% inc rease in gain per hectare over the 3.0 steer ha1.

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31 CHAPTER 3 EFFECT OF STOCKING RATES ON ANIMAL PERFORMANCE AND HERBAGE RESPONSES OF MULATO AND PENSACOLA BAHIAGRASS PASTURES Introduction Bahiagrass ( Paspalum notatum Flgge) is the main forage used for t he beef cattle industry in Florida because of its reliability and persistence under adverse climatic conditions and management practices. It is the most widely planted warm -season grass in Florida covering approximately 1 million hecta res. Nonetheless, ov erdependence on bahiagrass pastures has made the industry vulnerable to potential loss es of bahiagrass stands to pests and diseases infestations. There is a need to identify alternative warm -season grasses adapted to Florida Although, Brachiaria cv. Mulat o does not tolerate variations in edaphic and climatic conditions as well as bahiagrass does, it is adapted to infertile soils is known for its tolerance of prolonged drought and recovery after sporadic frost (Argel et al., 2005). These attributes suggest potential for use in South Florida forage livestock systems. Mulato, the first hybrid in the Brachiaria genus has been proven to be high in vigor and with good production potential in South and Central America ( Miles, 1999). Brachiariagrasses are the most widely grown forages in tropical America, occupying over 80 million h a (Boddey et al., 2004). Brachiaria species are popular among producers because they show rapid regrowth and good persistence under heavy or frequent defoliation (Rika et al ., 1991). Mul ato is drought tolerant and has the capacity to regrow during critical times of the year. It has crude protein ( CP ) concentrations fluctuating between 90 to 170 g kg1 with digestibility of 550 to 620 g kg1 (CIAT, 2005; 2006). It produced 25% more yield t han palisadegrass and signalgrass increasing animal productivity from 1 to 2 kg milk cow1 d1 over that achieved on palisadegrass cv. Marandu or palisadegrass cv. Toledo (Peters et al., 2003).

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32 There are no data available in the literature comparing Mula to and bahiagrass forage characteristics in Florida. However, Mislevy et al. (1996) stated that koronviagrass (Brachiaria humidicola) holds a distinct advantage over bahiagrass in digestibility. Koronviagrass had 77 (June July) and 80 g kg 1 (August Septem ber) greater in vitro digestible organic matter (IVDOM ) than Pensacola bahiagrass when grazed at a 21 -d frequency. In a clipping trial, mean IVDOM of koronviagrass from April to September was 120 g kg 1 greater than Pensacola (Mislevy and Everett, 1981). K oronviagrass and bahiagrass CP were 119 and 139 g kg 1 and IVDOM 550 and 499 g kg 1, respectively, early in June. Stocking rate (SR) is the most critical grazing management decision (Vendramini and Sollenberger, 2007). Stocking rate has profound effects o n forage and animal production. Animut et al., (2005) studied three SR (4, 6, and 8 animals) per 0.4-ha pasture, with equal numbers of sheep and goats using rotational grazing in 2 -wk grazing periods. Average daily gain decreased linearly as SR i ncreased ( 61, 51, and 47 g d1), and total live weight gain (LW G) increased linearly to 610, 759, and 933 g d1 for 4, 6, and 8 animals per 0.4 ha respectively. Hernndez Garay et al. (2004) reported a quadratic decrease in average daily gain ( ADG ) of weanling bull s grazing stargrass (Cynodon nlemfuensis Vanderyst) pastures as increased from 2.5 to 7.5 bulls ha1. Average daily gain decreased from 0.70 to 0.26 kg d1 in Year 1 and 0.65 to 0.35 kg d1 in Year 2 as SR increased from 2.5 to 7.5 head ha1. It is nece ssary to evaluate and develop management practices to optimize the utilization of Mulato in grazing systems in South Florida. The objective of this study was to evaluate the effects of SR on herbage mass (HM), accumulation rate (HMA), and nutritive value a nd performance of beef heifers grazing Mulato and bahiagrass pastures.

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33 Materials and Methods Experimental Site This experiment was conducted at the University of Florida Range Cattle Research and Education Center (RCREC), Ona FL (27.4o N) in 2007 and 2008. The soil at the research site was classified as a sandy siliceous, hyperthermic Alf ic Alaquod ( EauGallie sand ). These sandy soils are poorly drained with slow permeability. Prior to initiation of the grazing trial, mean soil pH (in water) was 6.0. Mehli ch -I (0.05 -M HCl + 0.0125M H2SO4) extractable P, K, Mg, and Ca in the Ap1 horizon (0 to 15-cm depth) we re 34, 72, 234, and 1600 mg kg1. Treatments and Design Treatments were the factorial arrangement of three SR [4, 8, and 12 heifers ha1] and two fora ge species ( Mulato and bahiagrass) in a randomized incomplete block design with three replicates for 4 and 12 heifers ha1 and two replicates for the 8 heifers ha1 treatment. Pastures (0.25 ha ) were stocked continuous ly. Pasture Management Grazing was in itiated in May of each year when adequate forage was available to support the livestock (18 May 2007 and 19 May 2008). Pastures received 150 kg N ha1 split in three equal applications (April, June, and August). The periods of the grazing trial were from 18 May through 10 Sep t. 2007 (116 d) and 19 May through 9 Sep t. 2008 (114 d). Plant and Animal Response Variables Pastures were sampled just prior to initiation of grazing and every 14 d during the grazing period. Herbage mass, HMA, and nutritive value (C P and IVDOM) were measured. Double sampling was used to determine HM The indirect measure was the settling height of a 0.25-m2 aluminum disk, and the direct measure involved hand clipping all herbage from 2 cm above soil level to the top of the canopy us ing an electric clipper. Every 28 d, one or two double samples

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34 were taken from each of the sixteen experimental units for a total of 20 per species Sites were chosen that represent ed the range of herbage mass present on the pastures. At each site, the dis k settling height was measured and the forage clipped. Clipped forage w ere dried for 72 h and weighed. At sampling every 14 d, 2 0 sites for disk measures were chosen by walking a fixed number of ste ps between each drop of the disk to ensure that all secti ons of the pasture were represented The average disk height of the 20 sites were en tered into the equation to predict actual herbage mass. Be cause these pastures were stocked continuously, a cage technique was used to measure herbage accumulation. Three 1 -m2 cages w ere placed in the pasture at the initial sampling date. Placement sites were chosen where the disk settling height was the same (1cm) as that of the pasture average. Disk settling height was recorded at a specific site and the cage placed. Aft er 14 d, the cage was removed and the new disk settling height recorded. Herbage accumulation was calculated as the change in herbage mass during the 14 d that the cage was present. At the end of each 14 d period, cages were moved to new locations on the pas ture with a current average disk settling height. Herbage allowance was calculated for each pasture as the average herbage mass (mean across t wo sampling dates within each 28-d period) divided by the average total heifer live weight during that period ( Sollenberger et al., 2005). Herbage CP and IVDOM concentration w as measured at the initiation of grazing and at every 14 d thereafter. Hand plucked samples w ere taken from each pasture. The objective w as to represent the diet consumed by the grazing animal and the technique involve d removing the top 5 cm of herbage at approximately 30 sites randomly chosen in each experimental unit Herbage was composite d across sites, dried at 60C for 48 h in a forced air oven to constant weight and ground in a Wiley mil l (Model 4, Thomas -Wiley Laboratory Mill, Thomas Scientific,

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35 Swedesboro, NJ) to pass a 1 -mm stainless steel screen. Analyses were conducted at the University of Florida Forage Evaluation Support Laboratory using the micro-Kjeldahl technique for N (Gallaher et al., 1975) and the two-stage technique for IVDOM (Moore and Mott, 1974). The heifers were Angus -sired (crossbred cows sired by Angus bulls) with initial LW of 386 38 kg. Cattle w ere weighed at initiation of the experiment and every 28 d thereafter. Wei ghts were taken at 0800 h following a 16 -h feed and water fast. Average daily gain was calculated each 28 -d period through the entire grazing season. G ain per hectare (GHA) was calculated for each pasture over the entire grazing season. Statistical Analys is Response variables were ADG, GHA, HM, HMA, HA, CP and IVDOM The data were analyzed using PROC MIXED of SAS (SAS Institute Inc., 2006 ) with forage spe cies, stocking rate, species x stocking rate ( main plot ), year ( subplot ), and month as fixed effects. M onth was a repeated measure. Replicate and its interactions were considered random effects. For pasture variables, the model used was: Y ijkl i + R j + S k + P l + (AR) ij + (AS) ik + (AP) il + (RS) jk + (RP) jl + (ARS) ijk + (ARP) ijl + (RSP) jkl + (ARSP) ijkl + e ijk Where Yijk is the dependent variable Rj is the stocking rate effect (main plot) Sk is the specie effect (main plot) Ai is the year effect (sub plot) Pl is the month effect (sub -sub -plot) (AR)ij is the year*stocking rate interaction (AS)ik is the year*specie interaction (AP)il is the year* month interaction (RS)jk is the stocking rate*specie interaction (RP)jl is th e stocking rate month interaction (ARS)ijk is the year*stocking rate*specie s interaction (ARP)ijl is the year*stocking rate*month interaction (RSP)jkl is the stocking rate*specie s month interaction (ARSP)ijkl is the year*stocking rate*specie s month intera ction eijkl is the error

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36 Single degree of freedom orthogonal polynomial contrasts were used to test stocking rate effects. Treatments were considered different when P < 0.05. Interactions not discussed in the Results and Discussion section were not signifi cant when P > 0.05. The means reported are least squares means and were compared using PDIFF (SAS Institute Inc., 2006). The correlation of HA and ADG was determined by a nonlinear minimization procedure using the PROC NLP of SAS (SAS Institute Inc., 1999) Results and Discussion Herbage Mass There was a linear decrease i n HM from 5.8 to 3.2 Mg ha1 as SR increased from 4 to 12 heifers ha1. There was a SR x species x month interaction for HM (Table 3 -1) Table 3 1. Stocking rate x specie s x month interact ion effects on herbage mass of bahiagrass and Mulato pastures Species/ Stocking r ate Month SE May June July August September heifers ha 1 ---------------Mg ha 1 --------------Mulato 4 5.6 c 7.3 b 8.2 a 4.9 d 5.2 cd 0.3 8 4.7 a 5.2 a 5.0 a 3.4 b 3.2 b 0.4 12 4.7 a 4.4 a 3.3 b 2.6 c 2.5 c 0.3 Contrast L L L L L Bahia grass 4 5.3 cd 4.3 d 5.2 cd 5.9 c 5.9 c 0.3 8 4.0 ab 3. 3 b 3.7 b 4.4 ab 4.4 ab 0.4 12 3.8 ab 2.7 cd 2.6 bc 2.8 bc 3.0 bc 0.3 Contrast L L L L L Monthly means within stocking rate followed by the same lower case letter are not different ( P > 0.05) Stocking rate effect within month and grass species. L = Linear ( P < 0.05) The interaction occurred because Mulato had similar or greater HM than bahiagrass in May, June, and July but lower HM in August and September at 4 and 8 heifers ha1, respectively. The less HM of Mulato in August and September was observed because of the above average rainfall in August (Table 1, Appendix A), which resulted in soils with exce ssive moisture. It was

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37 observed that HM of Mulato was negatively impacted by poorly drained soils conditions to a greater degree than bahiagrass. Mulato had greater HM at 12 heifers ha1 SR for May, June, and July but there was no difference in the subsequent months. There were no effects of SR on HM of Mulato in May. This occurred because the experimental period started in May with similar HM across experimental units and there was not enough time for the different treatments to impact HM. There was a year month interaction for HM ( Table 3 2). Herbage mass was greater in 2008 than 2007 for May, June and July but there was no difference in August and September. This was attributed to greater rainfall in those months in 2008 (Table 1, Appendix A). In 2007, HM was the least in June and similar on May, July, August, and September. Table 3 2. Year x month interaction effects on herbage mass of bahiagrass and Mulato pastures. Year Month SE May June July August September -----------------------Mg ha 1 ------------------------2007 3.8 a 2.7 b 3.5 a 4.1 a 4.1 a 0.2 2008 5.6 b 6.4 a 5.8 b 3.9 c 4.0 c 0.2 P < 0.01 < 0.01 < 0.01 0.23 0.49 SE 0.2 Monthly means within year followed by the same lower case letter are not different ( P >0.05) P va lue of y ear effect within month However, in 2008, HM increased in June and decreased in August and September. Greater HM was expected in June because of the greater rainfall. The decrease in HM in August and September 2008 happened because of above avera ge rainfall and excessive soil moisture. The greatest HM was observed in June of 2008 with an average of 6.4 Mg ha1 while least HM was observed in June of 2007 with an average of 2.7 Mg ha1.

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38 Herbage Mass Accumulation Rate There was a quadratic increase i n HMA as SR increased. Herbage mass accumulation was 106, 1 28, and 118 kg ha1 d1 for stocking rate 4, 8, and 12 heifers ha1, respectively. Pastures grazed at 8 heifers ha1 SR had stubble height of approximately 15 cm with sufficient leaf area to optim ize light interception that resulted in greater HMA. P astures stocked at 12 heifers ha1 had stubble heights of approximately 5 cm and the reduced leaf area remaining compromised HMA. Table 3 3. Stocking rate x month interaction effects on herbage mass ac cumulation rate of bahiagrass and Mulato pastures Stocking rate Month SE May June July August heifers ha 1 ---------------kg ha 1 d 1 -----------4 127 b 156 a 70 c 72 c 8 8 124 b 179 a 117 bc 91 c 9 12 104 bc 168 a 115 b 86 c 9 Contrast L Q Q Q SE 8 7 7 9 Monthly means within stocking rate followed by the same lower case letter are not different ( P > 0.05) Stocking rates effects within month. L = Linear; and Q = Quadratic ( P < 0.05) Conversely, pastures stocked at 4 heifers ha1 h ad excessive HM which probably resulted in self -shading, increased senescence rates, and finally decreased HMA. There was a stocking rate month interaction for HMA (Table 3 3) Herbage mass accumulation increased from May to June and subsequently decreas ed in July and August, however, the decrease was greatest in the 4 heifers ha1 SR. There was a year species x month interaction for HMA (Table 3 4 ) In 2007, HMA of Mulato and bahiagrass increased from May to June, decreased in July in bahiagrass, and increased in July in Mulato pastures. This increase in HM from May to June was observed because of the limited rainfall in May 2007 followed by adequate moisture conditions from June

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39 to August. In 2008, HMA of Mulato decreased linearly from June to August because of the excessive soil moisture, which limited plant growth. On the other hand, bahiagrass HMA increased from May to June and subsequently decreased in July and August for the same reason mentioned previously. Table 3 4. Year x species x month inter action effects on herbage mass accumulation rate of bahiagrass and Mulato pastures. Year/Species Month SE May June July August --------------kg ha 1 d 1 -------------2007 Mulato 111 b 164 a 121 b 143 a 10 Bahiagrass 3 8 c 69 b 108 a 71 b 10 P < 0.01 < 0.01 0.36 < 0.01 2008 Mulato 119 a 114 a 47 b 34 b 10 Bahiagrass 87 b 158 a 106 b 65 c 10 P < 0.01 < 0.01 < 0.01 0.48 Mo nthly means within year and species followed by the same lower case letter are not different (P > 0.05) P value for species effect within month and year. Bahiagrass is known for its tolerance to poorly drained soils conditions, and the decrease in HMA in July was not as great as the decrease in Mulato HMA. Mislevy (1985) described Pensacola bahiagrass as warm -season grass tolerant to short periods of flooding conditions. Excessive soil moisture decreases oxygen replenishment around the root system, respiration, energy production, and consequently plant growth (Salisbury and Ross, 1992). This may have caused lo w HMA in those months in addition to the likelihood of N leaching from the rooting zone. Nutritive Value There was a linear in crease in CP (from 125 to 136 g kg1) and IVDOM (591 to 611 g kg1) concentrations as SR increased from 4 to 12 heifers ha1. Th e increased in nutritive value

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40 occurred because of the most frequent appearance of new tissues and the greater leaf: stem ratio in the greater SR treatments. Stewart et al. ( 2007 ) reported that CP (140 vs. 99 g kg1) and IVDOM (505 vs. 459 g kg1) of bahi agrass pastures were greater for High SR (4.2 AU ha1) than L ow SR (1.2 AU ). HernadezGaray et al., (2004) also reported increase in CP and IVDOM of stargrass pastures as stocking rates increased from 2.5 to 7.5 bulls ha1. There was a stocking rate mont h interaction on herbage CP and IVDOM of bahiagrass and Mulato. Herbage CP was greater for 8 and 12 heifer ha1 treatments in all months but May. The lack of difference in May was likely because of the short period for detecting treatments differences afte r the start of the experiment. Herbage nutritive value increased from May to June in all treatments, likely because of the regrowth promoted by the greater rainfall in June. The effect of the N fertilization from April was delayed by the decreased rainfall in May and the plants likely responded to the N fertilizer in June, resulting in plants with greater CP concentrations. Positive IVDOM response to N fertilization of warm -season grasses is not consistently reported in the literature; however there are man y examples of this occurring (Newman et al, 2002; Vendramini et al., 2008) Table 3 5. Stocking rate x month interaction effects on crude protein of bahiagrass and Mulato pastures Stocking rate Month SE May June July August September heifers ha 1 ------------------------g kg 1 ------------------------4 115 b 144 a 137 a 112 b 118 b 5 8 115 c 159 a 154 a 133 b 128 b 6 12 102 c 152 a 159 a 134 b 134 b 5 Contrast L Q L L L SE 6 Monthly means within stocking rate followed by the same lower case letter are not different ( P > 0.05)

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41 Stocking rate effect within month. NS = Not significant P > 0.05; L = Linear; and Q = Quadratic. Vendramini et al. (2008) reported increases in IVDOM concentrations of Tifton 85 bermudagrass with increasin g N fertilization levels from zero to 80 kg ha1harvest1). The greater IVDOM of Mulato and bahiagrass in June and July may be due to increased proportion of new leaves caused by the delayed effects of the N fertilization. There was no difference in forage CP and IVDOM concentrations between the 8 and 12 heifers ha1 SR but there was a consistent decrease in nutritive value in August and September. The reduction in nutritive value in August and September is likely due to higher temperature which resulted in rapid growth and increased HMA. Table 3 6 Stocking rate x month interaction effects on in vitro digestible organic matter of b ahiagrass and Mulato pastures Stocking Rate Month SE May June July August September heifers ha 1 -----------------g kg 1 -----------------4 589 b 608 a 623 a 569 c 567 c 8 8 579 b 638 a 648 a 596 b 594 b 10 12 555 d 628 b 657 a 612 b c 607 c 8 Contrast L Q L L L SE 10 10 10 9 9 Monthly means within stocking rate followed by the same lower case letter are not different ( P > 0.05) Stocking rate effect within month. L = Linear; and Q = Quadratic ( P < 0.05 ). There was a year species x month interaction on herbage CP and IVDOM concentrations (Tables 3 7 and 3 8) In 2007, there were no d ifferences in herba ge CP between species from May to August; however Mulato had greater CP concentration in September. In 2008, Mulato had greater CP concentration than bahiagrass in May, June, and September but no differences were detected in other months. In 2007 and 2008, bahiagrass CP concentration increased from May to June with a subsequent decrease from July to September. The CP

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42 concentration of Mulato also increased from May to June, followed by a decrease in August and subsequent increase in September 2007 and 2008. The last N fertilization occurred in August and the increase in CP concentration in September was expected. The reason for the continued decrease in CP concentration in bahiagrass from July to September i s not known. Table 3 7. Year x species x month inte raction effect on crude protein concentration of bahiagrass and Mulato pastures. Year/Species Month SE May June July August September -----------------g kg 1 -----------------2007 Mulato 108 c 172 a 163 a 143 b 158 a 5 Bahiagrass 104 d 165 a 154 b 130 c 111 d 5 P 0.48 0.27 0.21 0.06 <0.01 2008 Mulato 121 b 144 a 139 a 112 c 123 b 5 Bahiagrass 108 d 125 b 142 a 119 c 112 cd 5 P 0.05 <0.01 0.71 0.29 0.10 SE 5 Monthly means within species followed by the same lower case letter are not different ( P > 0.05) P value for species effect within month and year In vitro digestible organic matter concentrations were greater in Mulato than in bahiagrass pastures during the entire experimental period. An increase in IVDOM was obs erved from May to July with a subsequent decrease in August and September. The reason for the consistent reduction in IVDOM concentration in August and September is likely due to higher temperature which resulted in rapid growth and increased deposition of lignin which reduces digestibility (Mislevy et al. 2001; Ezenwa et al., 2006). Mulato IVDOM concentrations were greater in July, August, and September 2007 than in the same months in 2008, however, the same trend was not observed in bahiagrass. The greater IVDOM concentrations in Mulato in 2007 may be due to reduced rainfall during the experimental period (Table A, A ppendix). It was observed that bahiagrass IVDOM concentration were less affected by climatic variation between years than

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43 Mulato. Climatic fac tors, primarily rainfall and temperature can have significant impact on forage nutritive value (Adesogan et al., 2006). Table 3 8. Year x species x month interaction effect on in vitro digestible organic matter concentration of bahiagrass and Mulato pastur es. Year/Species Month SE May June July August September ---------------g kg 1 -------------2007 Mulato 635 c 704 b 726 a 689 b 686 b 10 Bahiagrass 487 bc 578 a 578 a 508 b 482 c 10 P <0.01 <0.01 <0.01 <0.01 <0.01 2008 Mula to 635 d 674 b 699 a 640 c 657 c 10 Bahiagrass 538 b 541 b 567 a 530 b 529 b 10 P <0.01 <0.01 <0.01 <0.01 <0.01 SE 10 Monthly means within species followed by the same lower case letter are not different ( P > 0.05) P value for species effect within month and year Forage nutritive value tends to decline as forages regrow due to accumulation of stems and deposition of lignin in leaves and stems Forage regrowth in the summer may have lower nutritive value due to increased lignin deposition associate d with high temperatures, and in Florida due to increased growth rates and maturation associated with high rainfall (Adesogan et al., 2006). Herbage Allowance There was a quadratic effect of SR on HA of Mulato and bahiagrass pastures. Herbage allowances we re 2.4, 1.0, and 0.5 kg DM kg1 LW for 4, 8, and 12 heifers ha1, respectively. According to Sollenberger and Moore (1997), HA below 1.0 kg DM kg1 LW is an indicator of lack of sufficient forage for ad libitum consumption. It was observed that stocking ra te above 8 heifers ha1 had decreased HA and likely compromised animal performance.

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44 Table 3 9. Stocking rate x species x month interaction effect on h e rbage allowance of bahiagrass and Mulato pastures. Species/ Stocking rate Month SE May June July Augus t September heifers ha 1 -----------------kg DM kg 1 LW --------------Mulato 4 2. 4 c 3. 0 b 3. 5 a 2. 3 c 2. 6 c 0.2 8 1. 0 a 1. 0 a 1. 0 a 0. 8 a 1. 2 a 0.2 12 0. 7 a 0. 6 a 0. 5 a 0. 5 a 0. 5 a 0.2 Contrast L L L L L Bahiagrass 4 2. 5 a 1. 5 c 2. 0 b 2. 6 a 1. 9 bc 0.2 8 1. 0 a 0. 6 a 0. 8 a 1. 0 a 0. 9 a 0.2 12 0. 7 a 0. 3 a 0. 3 a 0. 4 a 0. 4 a 0.2 Contrast L L L L L SE 0.2 Monthly means within stocking rate followed by the same lower case letter are not different ( P > 0.05) Stocking rate eff ect within month and grass species. L = Linear ( P < 0.05) There was a stocking rate x species x month interaction effect on HA. The interaction occurred because there was a declined in HA of bahiagrass at 4 heifers ha1 from May to June with a subsequent increase from June to August. At the same stocking rate, Mulato HA increased from May to July and decline d subsequently The increase in HA of Mulato pastures from May to July may be due to increased HMA that resulted in greater HM and consequently greater HA. The same trend was not observed in bahiagrass likely due to a smaller increase in HMA and HM. It was observed that HA was below the desirable levels (1.0 kg DM kg1 LW) during the entire experimental period, on both forage species, for the 12 heifers ha1 SR treatment. Herbage allowance of Mulato pastures stocked at 8 heifers ha1 was below 1.0 kg DM kg1 LW in August and in bahiagrass pastures in June, July, and September. This is an indication that greater HMA and HM observed in Mulato pastures corre lated with greater HA levels throughout the experimental period for the 8 heifers ha1 SR

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45 Table 3 10. Year x month interaction effects on herbage allowance of bahiagrass and Mulato pastures. Year Month SE May June July August September ---------kg DM kg 1 LW -------------2007 1.8 a 1.2 b 1.6 a 1.8 a 1.6 a 0.1 2008 1.0 ab 1.2 a 1.1 ab 0.7 c 0.9 bc 0.1 P <0.01 0.68 <0.01 <0.01 <0.01 SE 0.1 Monthly means within year followed by the same lower case letter are not different ( P >0.05) P value for y ear effect within month There was a year x month interaction on HA of Mulato and bahiagrass pastures (Table 3 10). Herbage allowance was greater in 2007 than in 2008 for May, July, August, and September except in the month of June when HA wa s the same in 2008. The decreased HA in 2008 occurred because of the decreased HMA caused by above average rainfall. The interaction occurred because there was a decrease in HA in 2008 from July to August and in 2007, the HA was constant from July to Septe mber. Average Daily Gain There was no effect of grass species on ADG ( P = 0.32) nor was there species x SR interaction ( P = 0.83) There was a nonlinear correlation between HA and ADG (Fig. 3 1). Average daily gain increased with increasing HA up to 1.2 k g DM kg1LW, and remained constant at ADG at ~ 0.28 kg d1 when HA was above 1.2 kg DM kg1LW. The close relationship between HA and ADG supports the conclusion that the major factor affecting gains at high SR was herbage quantity Parkin and Boultwood (19 81) also observed that HA was the main

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46 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0 0.5 1 1.5 2 2.5 3 3.5 4 ADG (kg d 1 ) HA (kg DM kg 1 LW ) Figure 3 1. Nonlinear correlation between HA and ADG for Mulato and bahiagrass pastures stocked at 4, 8, and 12 heifers ha1. 0 0.1 0.2 0.3 0.4 0 4 8 12 Stocking rate (heifers ha-1) ADG (kg d-1) Fig ure 3 2 A verage daily gain of heifers Mulato and bahi agrass pastures stocked at 4, 8, and 12 heifers ha1. ADG = 0.013 + 0.2427*HA for HA 0 to 1.2 ADG = 0.28 for HA > 1.2

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47 factor determining animal production on stargrass pastures. For continuously stocked pearl millet [Pennisetum glaucum (L.) R. Br.], no increase in ADG above an HA of 3.3 was observed (McCartor and Rouqu ette, 1977). There was a decrease in ADG from May to August for the heifers stocked at 4 and 8 heifers ha1 treatments on bahiagrass and Mulato pasture, however, the decrease was greater for heifers grazing bahiagrass pastures. The decrease in ADG later i n the experimental period is likely due to a combination of water standing on the pasture, which caused discomfort of the animals, and decreasing nutritive value of the forage. During periods with frequent rainfall, animals reduce grazing time thereby redu cing DM intake (Butris and Phillips, 1987). A year x month interaction effect was observed on ADG of heifers grazing bahiagrass and Mulato pastures (Table 3 11) The interaction occurred because heifers grazing bahiagrass pastures had greater ADG in May 2008 but a more rapid decrease in ADG in 2008 than 2007. The reason for the greater decrease in ADG in 2008 was likely because of excessive rainfall (Table A 1) and water standing in the pastures that likely caused discomfort of the animals. Despite great er HM, ADG was consistently lower in 2008. Table 3 11. Year x month interaction effects on ADG of Mulato and b ahiagrass pastures. Year Month SE May June July August -----------------k g d 1 ---------------2007 0. 66 a 0.09 b 0. 13 b 0. 12 c 0.05 2008 1. 03 a 0. 12 b 0. 23 c 0. 07 c 0.05 P <0.01 0.75 <0.01 0.55 SE 0.05 Monthly means within year followed by the same lower case letter are not different ( P >0.05) P value for y ear effect within month There was a specie s SR month interac tion on ADG of heifers grazing Mulato and bahiagrass pastures (Table 3 12) It was observed that animals grazing pastures stocked at the 12

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48 heifers ha1 SR presented decreased performance throughout the experimental period compared to 4 and 8 heifers ha1, primarily because of the limited forage quantity mentioned previously. The only exceptions were observed in May and August. The animals had greater ADG in May was possibly due in part to residual of gut fill effects resulting from the transition of the an imals from cool -season annual pasture to warm -season grass pasture. Table 3 12. Stocking rate x specie s x month interaction effects on ADG of Mulato and b ahiagrass pastures. Species/ Stocking rate Month SE May June July August heifers ha 1 --------------kg d 1 -----------Mulato 4 0. 79 a 0. 18 b 0. 22 c 0. 05 d 0.08 8 0. 83 a 0. 23 b 0. 18 b 0. 15 c 0.1 12 0. 74 a 0. 07 b 0. 33 c 0. 07 b 0.08 Contrast Q Q L L Bahiagrass 4 1. 05 a 0. 20 b 0. 33 d 0. 02 c 0.08 8 0. 85 a 0. 15 b 0. 02 bc 0. 11 c 0.1 12 0. 83 a 0. 06 b 0. 09 bc 0. 32 c 0.08 Contrast L L Q L SE 0.08 0.08 0.09 0.09 Monthly means within stocking rate followed by the same lower case letter are not different ( P > 0.05) Stocking rate effect within month and grass spe cies. L = Linear; and Q = Quadratic ( P > 0.05). Gain per Hectare There was a quadratic effect of SR on GHA for bahiagrass and Mulato with means of 190, 353, and 218 k g ha1 for 4, 8, and 12 heifers ha1 respectively. The SR of 8 heifers ha1 resulted in the greatest GHA. Understocked pastures accumulate excess forage that becomes lower in nutritive value resulting in low gain per unit land area (Mott and Lucas, 1952).

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49 0 50 100 150 200 250 300 350 400 0 4 8 12 GHA (kg ha 1 ) Stocking rate (heifers ha 1 ) Fig ure 3 3. Gain per ha of heifers grazing Mulato and bah iagrass pastures stocked at 4, 8, and 12 heifers ha 1. Hernandez Garay et al. (2004) studied the effect of stocking rate on weanling bulls grazing stargrass. Animal ADG decreased quadratically with increasing stocking rate from 1.3 to 3.8 AU (500 kg LW) h a1. The GHA was maximized at stocking rates of ~ 2.5 AU ha1. Summary and Conclusions Mulato had greater HM at all SR than bahiagrass. Herbage mass accumulation was the greatest at 8 heifers ha1for both grasses. Mulato showed greater HMA than bahiagrass in May, June and August. I n September, the greater HMA resulted in decreased CP and IVD O M concentrations. In general, CP and IV DOM of Mulato were greater in August and September than in May. Herbage CP concentration of Mulato was not affected by SR in May, July and August, but was greater at 8 than 4 heifers ha1 in June and September. In vitro digestible organic matter

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50 concentrations were greater at 8 than 4 heifers ha1 across the grazing period except in May. Mulato had greater IVDOM than bahiagrass thr ough out the experimental period. St ocking rate was the most influential factor in GHA and ADG Increasing SR from 4 to 12 heifers ha1 linearly decreased ADG. Gain per hectare was the greatest at 8 heifers ha1. There were no conclusive differences on ADG and GHA among species. Year and month significantly impact ed ADG. In general, Mulato had superior HM, HMA, and nutritive value than bahiagrass; however, it was observed that Mulato was more negatively impacted by flooded soils than bahiagrass. The slightl y superior forage HMA and nutritive value of Mulato did not result in greater animal performance. Stocking rate was the primary determinant of animal performance on Mulato and bahiagrass pastures. There is potential of using Mulato as an alternative forage for bahiagrass pastures in South Florida, however, Mulato should be planted in areas with well -drained soils and grazed at SR which allow HA of 1.2 kg DM kg1 LW or greater.

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51 CHAPTER 4 EFFECT OF STUBBLE HEIGHT AND HARVEST FREQUENCY ON FORAGE PRODUCTIO N AND NUTRITIVE VALUE OF BRACHIARIA CV. MULATO Introduction Bahiagrass ( Paspalum notatum Flgge) has been the primary forage species used for beef cattle producers in Florida due to its wide environmental adaptation and tolerance to minimal management inputs. However, more than 150,000 ha of bahiagrass pastures were damaged by mole cricket (Scapteriscus spp.) in Florida between 1996 and 2000 (Adjei et al. 2001). Damage to bahiagrass pastures by armyworms ( Pseudaletia unipuncta), grasshoppers (Melanoplus d ifferentialis ), and loss of stands due to mole crickets has stimulated a search for other grasses adapted to the S outh Florida environment Brachiaria species are popular among producers in tropical areas of the world because they show rapid regrowth and good persistence under heavy or frequent defoliation (Rika et al ., 1991). A hybridization program was initiated at the Centro Internacional de Agricultura Tropicale (CIAT) with the objective to produce improved brachiariagrass cultivars with outstanding agronomic characteristics, greater range of adaptation, higher biomass production and nutritional quality, and resistance to Rhizoctonia and multiple spittle bug species This effort generated an apomictic hybrid, Mulato (CIAT, 2000) which is the first hybrid in the Brachiaria genus. Although, Mulato does not tolerate variations in edaphic and climatic conditions as well as bahiagrass does, it is adapted to the infertile soils of Central and South America. According to Peters et al. (2003) Mulato produce d 25% more dry matter yield (DMY) than palisadegrass (Brachiaria brizantha) and signalgrass (Brachiaria humidicola), increasing animal productivity from 1 to 2 kg milk cow1 d1 over that achieved on Marandu or Toledo palisadegrass. Moreover, Mulato has shown superior nutritive value when compared to other brachiarias

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52 (CIAT, 2006). Mulato is known for its tolerance of prolonged drought and rapid recovery after sporadic frost (Argel et al., 2005) Because of these desirable characteristics, Mulato may be a po tential warm -season grass for use in South Florida forage livestock systems. Production and nutritive value of warm -season grasses are greatly affected by management practices, including regrowth interval and stubble height. Forage quality tends to decline as forages mature due to accumulation of stems and deposition of lignin in leaves and stems (Adesogan et al., 2006). Arthington and Brown (2003) reported that increas in g Pensacola bahiagrass regrowth interval from 4 to 10 wk resulted in decreased CP and digestibility. Additionally, f orage regrowth in the summer may have lower quality due to increased lignin deposition associated with high temperatures, and in Florida due to increased growth rates and maturation associated with high rainfall (Adesogan et al ., 2006). Brown and Mislevy (1988) reported summer yields of Pensacola were greater than spring yields, but crude protein ( CP ) and in vitro digestible organic matter (IVDOM ) concentrations were lower. Chaparro and Sollenberger (1997) reported frequent defoliation to short stubble height resulted in greatest IVDOM of Mott elephantgrass ( Pennisetum purpureum Schum.), while herbage harvested infrequently to short stubble was least digestible. When defoliated frequently, most of the harvested material of elep hantgrass consisted of leaf blade and less leaf sheath and stem (Chaparro et al., 1995). Beaty et al. (1970) indicated that close clipping (0 to 2.5 cm) of Pensacola bahiagrass produced highest DMY; however, stand deterioration was evident with frequent harvest s Mislevy and Everett (1981) found that total DM Y of Pensacola and Argentine bahiagrasses were greater at a 5 than a 10-cm stubble height while Beaty et al. (1968) reported total DM Y of Pensacola generally increased as stubble height decreased across

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53 six stubble heights. Similarly, Pedreira and Brown (1996) reported that annual yields of Pensacola and Tifton 9 were greater at 3.5 than 10 cm. Frequent defoliation may have negative effects on plant persistence. Stem base rhizome, stolon, and ro ot mas s are generally depleted under conditions of frequent and severe defoliation (Chambliss, 1999; 2000; and 2006). According to Youngner (1972), root growth is generally reduced by defoliation as results of the reduction of photosynthetically active tis sue and shortage of carbohydrates for root growth. Therefore, it is important to establish warm -season perennial grass pastures that tolerate different defoliation regimens while maintaining forage production persistence, and nutritive value. The general objective of this study was to evaluate the effect of harvest management strategies on Mulato The specific objectives of this study were to evaluate the effects of stubble height and regrowth interval on nutritive value, herbage mass accumulation, and pe rsistence of Mulato Materials and Methods Experimental Site This experiment was conducted at the University of Florida Range Cattle Research and Education Center (RCREC), Ona FL (27o26'N, 82o55'W) from 17 Aug. to 9 Nov. 2007. The soil at the research si te was classified as sandy siliceous, hyperthermic Alf ic Alaquod ( EauGallie sand ). These sandy soils are poorly drained with slow permeability. Prior to initiation of the clipping study, mean soil pH (in water) was 6.3. Mehlich I (0.05-M HCl + 0.0125M H2SO4) extractable P, K, Mg, and Ca in the Ap1 horizon (0 to 15-cm depth) we re 22, 63, 128, and 980 mg kg1.

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54 Treatments and Experimental Design Treatments were the factorial arrangement of three stubble heights (2.5, 7.5, and 12.5 cm ) and two harvest freque ncies ( 2 and 4 wk) in a randomized complete block design with four replicat es. Mulato plots w ere planted in May 2007 using the seeding rate of 10 kg ha1. In July 2007, the plots receive d 40 kg N ha1, 17 kg P ha1, and 66 kg K ha1 to stimulate growth and provide maintenance P and K. An additional 40 kg N ha1 w as applied after every 28 d harvest. Total -season N fertilization was 120 kg N ha1. Forage Measurements Plot size was 3 x 2 m with 1 -m alley between plots. Plots were staged to the treatment stubbl e height s on 17 Aug. 2007. At harvest dates, herbage was clipped to the target stubble height from two representative 0.25 -m2 quadrats per plot. Remaining herbage was clipped to the same stubble height using a sickle bar mower and removed. Herbage accumula tion data are presented by month and data from a given month are the total of one harvest of 4 -wk treatments or 2 harvests of the 2-wk treatment Forage samples were dried at 60oC to a constant weight, weighed, and ground in a Wiley mill (Model 4 Thomas -Wi ley Laboratory Mill, Thomas Scientific, Swedesboro, NJ) Herbage N concentration was determined by combustion using a N analyzer (Flash EA 1112 Series) and CP calculated as N x 6.25. The in vitro digestible dry matter concentration ( IVD DM ) was determined u sing the ANKOM (2005) adaptation of the Van Soest et al. (1966) method in an ANKOM Daisy II Incubator and ANKOM 200 Fiber Analyzer (ANKOM Technology, Macedon, NY) Mulato cover was determined visually by two observers at the end of the experimental perio d using a 1 -m2 quadrat divided in to 10 cm x 10-cm squares.

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55 Statistical Analysis Response variables were proportion of Mulato coverage, HMA, CP, and IVDDM concentration. The data were analyzed using PROC MIXED of SAS (SAS Institute Inc., 2006 ) with stubbl e height regrowth interval, month, and their interactions were fixed effects. Month was considered a repeated measure. Block and its interactions were random effects. Single degree of freedom orthogonal polynomial contrast was used to test stubble height effects. Treatments were considered different when P < 0.05. Interactions not mentioned in the text were not significant ( P > 0.05). The means reported are least squares means and were compared using PDIFF (SAS Institute Inc., 2006). For plot variables, t he model used was: Y ijkl i + S j + H k + B m + (PS) ij + (PH) ik + (SH) jk + (PSH) ijk + e ijk Where Y ijkl is the dependent variable S j is the stubble height effect (main plot) H k is the regrowth interval effect (main plot) P i is th e month effect (sub -plot) Bm is the block effect (SH) jk is the stubble height x regrowth interval interaction (PS) ij is the month x stubble height interaction (PH) ik is the month x regrowth interval interaction (PSH) ijk is the month x stubble height x regr owth interval interaction e ijkm is the error Results and Discussion H erbage M ass Accumulation There was a decrease in HMA from 2.6 to 1.9 Mg ha1 as stubble height increased from 2.5 to 12.5 cm. The quadratic effect occurred because HMA decreased from 2.5 to 7.5 cm but then remained relatively constant. Hidalgo (2004) found similar trends in the effects of stubble height on HMA of Mulato in South America. There was no difference in Mulato HMA when harvested above 7.5 cm stubble height (0.13 Mg ha1 d1 at 10cm and 0.14 Mg ha1 d1 at 20cm stubble ).

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56 Gates et al (1999) reported that low er cutting stubble heights resulted in greater HMA in bahiagrass plots. Herbage mass accumulation was maximized by cutting at low er stubble height and 8 -wk regrowth inter val (7.0 M g ha1) in the first year, however, the 4 -wk regrowth interval and low cutting height produced the greatest yield (11. 2 M g ha1) in the second year. Corroborating with the current study, the authors concluded that stubble height consistently affe cted HMA. There was a regrowth interval month interaction for HMA. The interaction occurred because HMA declined from 3.0 to 0.8 Mg ha1 from August to October when harvested at 2 wk, however, HMA increased from August to September and subsequently decr eased in October in the 4 -wk treatment. The 4-wk regrowth interval had greater HMA than the 2 -wk in September, less in August, and similar in October (Table 4 1). Shorter daylengths and lower temperatures (Table 1, Appendix A) likely decreased Mulato growt h from August to October (Sinclair et al., 2003) Hidalgo (2004) reported that Mulato had greater HMA when cut every 35 d (4.6 Mg ha1) compared to 28 d (4.0 Mg ha1) and 21 d (2.6 Mg ha1) regrowth interval s In addition, below average rainfall (more than 25.7 mm less than normal) may have contributed to decreased HMA in October. Table 4 1. Regrowth interval x month interaction effects on herbage mass of Mulato forage. Regrowth interval Month SE August September October wk ---------------Mg ha 1 ----------2 3. 0 a 2. 6 b 0. 8 c 0.1 4 2. 5 b 3. 2 a 1. 0 c 0.1 P <0.01 <0.01 0.28 SE 0.1 Monthly means within regrowth interval followed by the same lower case letter are not different ( P > 0.05) P value for effect of regrowth interval within m onth.

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57 Mislevy and Everett (1981) found that total DM yields of Pensacola bahiagrass and koroniviagrass ( Brachiaria humidicola) were greater at 5 than 10-cm stubble when clipped every 30 d. Koroniviagrass showed no difference in yield ( 2.9 M g ha1) than Pensacola (2.5 M g ha1) a t the 5 cm stubble height. There was also no difference in DM yield (1.8 M g ha1) at 10 cm between both grasses. Forage Nutritive Value There was a regrowth interval stubble height and regrowth interval x month interaction s on herbage CP concentration. Herbage CP of Mulato was the greatest when cut to 2.5 cm at 2 wk regrowth interval and the least when cut to 12.5 cm at 4wk regrowth interval (Table 4 2). The regrowth interval x stubble height interaction occurred because the re was a linear decline in CP concentration from 200 to 160 g kg1 as stubble height increased from 2.5 to 12.5 cm at the 2 wk regrowth interval S tubble height did not affect CP concentrations at the 4 wk regrowth interval. Herbage CP was greater at 2 wk compared with 4 wk regrowth interval at all stubble heights. The more frequent harvest at shorter stubble heights resulted in a greater proportion of new leaf tissue and decreased appearance of stems, resulting in plant material with greater CP concent ration. Table 4 2. Regrowth interval x stubble height interaction effects on crude protein of Mulato forage Regrowth interval Stubble height (cm) Contrast 2.5 7.5 12.5 wk --------------g kg 1 -------------2 200 180 160 L 4 130 130 120 NS P <0.01 <0.01 <0.01 SE 6 Effect of stubble height within regrowth interval; NS = Not significant ( P > 0.05); L = L inear, (P <0.05). P value for regrowth interval effect within a stubble height

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58 Crude protein concentration of Mulato decreased as regrowth interval increased This response was similar to that reported by Hidalgo (2004) who found that CP decreased from 100 to 92 g kg1 as harvest interval of Mulato was delay ed from 21 to 35 d Vendramini et al. (2008) found tha t there was a linear increase in CP concentration of Tifton 85 bermudagrass ( Cynodon sp.) with increasing N fertilization, but the rate of increase was greater for the 2 than the 4 -wk regrowth interval. Herbage CP was affected by a regrowth interval month interaction (Table 4 3). When harvested at 2 wk, herbage CP was greater across all months compared to harvests at 4 wk. The interaction occurred because t here was no difference in herbage CP between harvests in August and October at the 2 wk regrowth interval. However, herbage CP concentration increased from August to October when forage was harvested at a 4 wk regrowth interval. Herbage CP was lowest at both 2 and 4 wk in September The greater CP concentration in October may be due to decreased HMA and less of a N dilu tion effect. Similar results were reported by Vendramini et al. (2008) with Tifton 85 bermudagrass. Tifton 85 had greater CP concentration when harvested at a 2 wk than a 4 wk regrowth interval (160 vs. 120 g kg1 for 2 and 4 wk, respectively). Table 4 3. Regrowth interval x month interaction effects on crude protein of Mulato forage. Regrowth interval Month SE August September October wk -----------g kg 1 -----------2 190 a 170Ab 190 a 4 4 130 b 110 c 150 a 4 P <0.01 <0.01 <0.01 SE 4 Monthly means within regrowth interval followed by the same lower case letter are not different ( P > 0.05). P value for effect of regrowth interval within month.

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59 Arthington and Brown (2005 ) found that increased forage maturity (10 -wk regrowth) wa s associated with 38% l ower CP concentration compared with harvesting at 4 -wk regrowth, when averaged across several different species of warm -season grasses Arthington and Brown (2003) also reported that increases in Pensacola maturity from 4 to 10-wk r egrowth resulted in decreased CP and digestibility Haddad et al (1999) reported a decline in CP of Pensacola bahiagrass from 20 to 50 d of regrowth after cutting ( from 145 to 97 g kg1). The decrease in CP concentration at longer regrowth intervals in w arm -season grasses is attributed to N dilution effects caused by greater HMA and associated deposition of cell wall There was a linear decrease in CP concentration from 170 to 140 g kg1 as stubble height increased from 2.5 to 12.5 cm. There was a stubbl e height month interaction on herbage CP of Mulato. The CP of Mulato was greatest when cut in October at 2.5 cm and least when cut in September at 12.5 cm. There was a linear decline in CP concentration as stubble height increased from 2.5 to 12.5 cm in all months The reason for consistent reduction in CP in September is due to higher temperature which resulted in rapid growth and increased HMA. Table 4 4. Stubble height x month interaction effects on crude protein concentration of Mulato forage. Stubb le height Month SE August September October cm -----------------g kg 1 ---------------2.5 170 b 150 c 190 a 5 7.5 160 b 140 c 170 a 5 12.5 140 b 130 c 150 a 5 Contrast L L L SE 5 Monthly means within stubble height followed by the sam e lower case letter are not different ( P > 0.05). Effect of stubble height on CP concentration within month; L = Linear ( P < 0.05). A similar trend in nutritive value was reported by Mislevy et al. (2005) on bahiagrass plots. The greatest bahiagrass CP concentrations were reported in the fall, October (157 g kg1) and

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60 December (177 g kg1), while lowest CP was always found in the summer ( June 113 g kg1 ; August 122 g kg1). There was a regrowth interval month interaction on IVDDM. Herbage digestibil ity of Mulato was the greatest in October and the least in September at the 4 wk regrowth interval (Table 4 5 ). Mulato had the greatest IVDDM concentrations in October due to slower growth rates, lower growth temperature and less mature herbage. The prese nce of a higher proportion of young, less mature leaf and stems resulted in greater IVDDM for the 2 wk than 4 wk regrowth interval in August and September, but in October the response was reversed, likely associated with slower forage growth rates that m onth. There was an increase in IVDDM as time progressed from August to October at 2 wk regrowth interval (Table 4 5) A quadratic trend was observed for IVDDM harvested at 4 -wk regrowth interval. The digestibility was 690 g kg1 in August, decreased to 66 0 g kg1 in September and increased to 780 g kg1 in October. Table 4 5. Regrowth interval x month interaction effects on in vitro digestible dry matter concentration of Mulato forage. Regrowth interval Month SE August September October wk -------------g kg 1 ---------------2 710 b 740 a 740 a 8 4 690 b 660 c 780 a 8 P 0.04 <0.01 <0.01 SE 8 Monthly means within a regrowth interval followed by the same lower case letter are not different ( P > 0.05) P value for effect of regrowt h interval within month. Arthington and Brown (2005 ) reported decreased IV D OM when harvest was delayed from 4 to 10 wk (average IV D OM decrease = 11, 9, and 62 g kg1 for bahiagrass, bermudagrass, and stargrass, respectively. Haddad et al (1999) reported a decline in IVDDM of Pensacola bahiagrass from 20 to 50 d of regrowth after cutting from 678 to 448 g kg1. Gates et al (1999)

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61 reported that forage IVDMD ranged from more than 600 g kg1 early in the season to 400 g kg1 or less by the end of the growing season for Pensacola, Tifton 9 and RRPS cycle 14. Cuomo et al. (1988) observed a quadratic trend in IVDDM response to harvest frequency of three cultivars of bahiagrass. Digestibility declined from 595 (20 d) to 587 (30 d) and increase d slightly to 592 g kg1 (40 d) when harvest at 5 cm stubble height. There was a stubble height month interaction on IVDDM concentrations of Mulato (Table 4 6 ). For all stubble heights IVDDM concentration increased from August to October but the increase was greater for the 2.5 cm stubble height treatment than the others The decreased HMA in October and cooler weather resulted in less mature, more digestible material. Table 4 6. Stubble height x month interaction effects on in vitro digestible dry matter concentration of Mulato forage. Stubble height Month SE August September October cm -------------g kg 1 ---------------2.5 660 b 660 b 750 a 10 7.5 710 b 710 b 780 a 10 12.5 720 b 720 b 750 a 10 Contrast L L Q SE 10 Monthly means within stu bble height followed by the same lower case letter are not different ( P > 0.05). S tubble height effect within month; L = Linear ( P < 0.05) ; and Q = Quadratic ( P < 0.05) Th ese result s agree with Mislevy et al. (2005) who report ed greatest bahiagrass IV D OM in October (542 g kg1) and December (587 g kg1), while lowest IV D OM w as always found in July (467 g kg1) and August (482 g kg1). T here was regrowth interval stubble height interaction for Mulato ground cover (Table 4 7). Continuous clipping of Mul ato at a 2 wk interval at 2.5 cm stubble height tended to decrease persistence and increase bare ground. There was no difference in Mulato cover associated with clipping every 2 to 4 wk at 2.5 cm but there was an increase in Mulato ground

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62 cover when har vested at 4 wk compared to 2 wk at 7.5 cm stubble height Increasing stubble height from 7.5 to 12.5 increased the ground cover of Mulato at 2 wk regrowth interval, but there was no difference in ground cover between 7.5 to 12.5 cm stubble heights at 4 wk regrowth interval. According to Beaty et al. (1970) P ensacola bahiagrass stands were gradually reduced after frequent clipping due to a re duction in root and stolon mass and subsequent reduction in nonstructural carbohydrates available for regrowth. Tab le 4 7. Regrowth interval x stubble height interaction effect s on percentage cover of Mulato. Regrowth interval Stubble height (cm) SE 2.5 7.5 12.5 W k ------------% ------------2 63 b 67 b 91 a 4 4 70 b 86 a 84 a 4 P 0.20 <0.01 0.15 SE 4 Stubble height means within a regrowth interval followed by the same lower case letter are not different ( P > 0.05). P value for effect of regrowth interval within stubble height. Mislevy and Everett (1981) reported Pensacola and Argentine stands harvested to 10 cm every 30 d had superior stand persistence and minimal weed encroachment than plants harvested to 5 cm. Mislevy at al. (1989) studied the responses of three stargrasses to treatment combinations of grazing intensity (stubble heights of 5 25 cm) and frequency (pastures grazed at plant heights above stubble ranging from 0 60 cm). The authors concluded that stubble height was the primary factor that affected persistence of stargrass. Allowing a postgraze stubble height of 15 25 cm resulted in lowest weed cover for all cultivars.

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63 Summary and C onclusions Mulato had greater HMA when harvested at shorter stubble. The effects of regrowth interval on HMA were not conclusive in the first year of defoliation Monthly HMA of Mulato was greater at 2 t han 4 wk regrowth interval. In general, CP and IVDD M of Mulato were greater in October than August and September. Herbage CP concentration of Mulato was greater at 2 than 4 wk regrowth interval, regardless of stubble height. In vitro digestible dry matter concentrations were greater at 2 than the 4 wk regrowth interval through the experimental period except in October. Stubble height was the most influential factor in Mulato persistence. The 2.5 cm stubble height treatment resulted in the least Mulato co ver, regardless of the regrowth interval. When harvested at 7.5 cm stubble height, the 4 wk regrowth showed superior cover than the 2 wk regrowth interval. The results from this study imply that harvesting Mulato in August and September at 7.5 cm stubb le every 4 wk regrowth interval enhance s HMA while maintaining the Mulato stand. Conversely harvesting Mulato at 2.5 cm stubble height increases its HMA but decreases Mulato stands. The 2 wk regrowth interval resulted in forage with greater nutritive va lue. The decision of the regrowth interval to harvest Mulato is dependent on the nutrient requirements of the animals that will consume the forage.

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64 CHAPTER 5 SUMMARY AND CONCLUSIONS Bahiagrass has been the primary warm -season pasture grass used in cow -c alf production systems in Florida due to its wide environmental adaptation and toleranc e to minimal management inputs. However, there is a necessity to evaluate warm -season grasses with potential to complement bahiagrass forage systems. Brachiaria cv. Mula to does not tolerate variations in edaphic and climatic conditions as well as bahiagrass but it is adapted to the infertile soils of Central and South America and merits evaluation in Florida Production and nutritive value of warm -season grasses are gre atly affected by management practices, such as regrowth interval and stubble height. Regrowth interval and season of year play major roles in determining forage nutritive value Forage nutritive value tends to decline as forages regrow due to accumulation of stems and deposition of lignin in the cell wall of leaves and stems (Adesogan et al., 2006). Warm -season grasses decrease crude protein ( CP ) and in vitro digestible organic matter (IVDOM ) concentrations with advancing maturity (Ball et al., 2001), prima rily due to reproductive stem elongation (Coleman et al., 2004). Forage regrowth in the summer may have lower quality due to increased lignin deposition associated with high temperatures, and in Florida due to increased growth rates and maturation associat ed with high rainfall (Adesogan et al., 2006). On graz ed pasture s tocking rate has a profound effect on forage characteristics and animal performance ( Burns et al., 1989). It is important to understand the effects of defoliation intensity on plant persist ence, productivity and nutritive value in order to develop best management recommendations for grazing systems (Chaparro et al. 1995, 1996). The objectives of this study were i) to determine forage characteristics and animal performance of heifers grazi ng Mulato and bahiagrass pastures (Chapter 3); and ii) to determine

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65 the effects of defoliation management on herbage production, nutritive value, and persistence of Mulato (Chapter 4). The overall goal of the research effort was to assess the potential of using Mulato in grazing systems and develop a range of management practices to optimize the utilization of Mulato in South Florida. Mulato and Bahiagrass Grazing Study Herbage Y ield and Nutritive Value The periods of the grazing trial were from 18 May th rough 10 Sep t. 2007 (116 d) and 19 May through 9 Sep t. 2008 (114 d). Treatments were the factorial arrangement of three stocking rates [4, 8, and 12 heifers (LW = 350 21 kg) ha1] and two forage species ( Mulato and bahiagrass) in a randomized incomplete block design with three replicates for 4 and 12 heifers ha1 and two replicates for the 8 heifers ha1 treatment. Pastures were 0.25 ha and were stocked continuous ly Double sampling w as used to determine herbage mass (HM) For laboratory analyses, harvest ed samples collected every 14 d were analyzed for IVDOM and N concentration. Be cause these pastures were stocked continuously a cage technique was used to measure herbage accumulation Three 1 -m2 cages w ere used per pasture, and d isk settling height was r ecorded at specific site s where cage s were placed. Herbage allowance (HA) was calculated for each pasture as the average herbage mass (mean across t wo sampling dates within each 28d period) divided by the average total heifer live weight during that period (Sollenberger et al., 2005). Cattle w ere weighed at the initiation of the experiment an d every 28 d thereafter. Average daily gai n and gain per hectar e was calculated each 28 -d period through the entire grazing season. There was a linear decrease in HM a s stocking rate increased. Mulato and bah ia grass HM were affected by climatic variation during experimental period. Mulato had greater HM than bahiagrass in the early months of the experimental period but presented similar HM in August

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66 and September. It wa s observed that Mulato decreased HM in greater magnitude than bahiagrass in conditions of excessive soil moisture. In addition, pastures stocked at 12 heifers ha1 had a more pronounced decrease in HM from May to September than the other stocking rate trea tments. In 2008, pastures had greater HM in May, June, and July than in 2007. This occurred because of more favorable rainfall conditions in 2008. On the other hand, HM increased from July to September in 2007, but a decrease was observed during the same period in 2008. There was a quadratic effect of stocking rate on H MA. Herbage mass accumulation was greatest at the 8 heifer ha1 stocking rate treatment. Mulato had greater HMA than bahiagrass during the experimental period. Bahiagrass increased HMA from May to June and July with a subsequent decrease in August. There was no dif ference in monthly HMA of Mulato in 2007. However there was a significant decrease from June to August in 2008. The decreased occurred because of the excessive soil moisture condit ions mentioned previously. Mulato showed greater HMA than bahiagrass in May, June and August. In 2008, HMA of Mulato decreased linearly from June to August because of the excessive soil water concentration that limited plant growth There was a linear de crease in CP and IVDOM concentrations of Mulato and bahiagrass as stocking rates increased from 4 to 12 heifers ha1. Herbage CP concentration of Mulato and bahiagrass was greater in the first year than in the second year. Mulato showed greater herbage CP concentration than bahiagrass in September in both years Mulato had greater IVDOM than bahiagrass throughout the entire experimental period Animal Performance Herbage allowance (HA) decreased below 1.0 kg dry matter ( DM ) kg1 liveweight ( LW ) when stocki ng rate was raised above 8 heifers ha1. This likely compromised animal performance and was consistent with previous observations which indicat e lack of sufficient forage for ad libitum consumption at this HA (Sollenberger and Moore, 1997)

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67 There was a li near decrease in average daily gain (ADG) with increasing SR from 4 to 12 heifers ha1. There was significant reduction in ADG on bahiagrass and Mulato pastures by mid summer The decrease in ADG later in the experimental period is likely due to a combinat ion of water standing on the pasture, which caused discomfort of the animals, and decrease d forage nutritive value. Average daily gain was the greatest at 8 least at 12 heifers ha1. Gain per hectare was the greatest at 8 heifers ha1. Under stocked pastu res accumulate forage that becomes both underutilized and hence the low gain per unit land area basis (Mott and Lucas, 1952). There were no c onclusive differences i n ADG and GHA between species Defoliation Management Response Treatments were the factorial combinations of two regrowth intervals (2 and 4 wk) and three stubble heights ( 2.5, 7.5, and 12.5 cm ) evaluated in 1 yr. Treatments were replicated four times in a completely randomized design. Mulato plot s were planted in May 2007. Plot size was 3 x 2 m with a 1 -m alley between plots. Plots were staged to a 15-cm stubble on 17 Aug 2007. Herbage accumulation data were reported for a given 4 wk period based on one harvest of the 4 wk treatment and two harvests of the 2 -wk treatment. For laboratory analyse s, harvested samples were analyzed for IVDOM and N concentration Mulato cover was quantified at the start and end of the experiment al period to determine stand persistence. Herbage M ass A ccumulation and Nutritive Value Mulato produced low yield in early f all and excellent yield during summer. The decline in yield in autumn can be attributed to shorter daylengths (Sinclair et al., 2003) and possibly to the below average rainfall ( 26 mm less than normal in October) The rate of decline in yield toward autum n was less at a 2 wk lowest frequency than at 4 wk. Total herbage yield of Mulato when clipped at 2 wk (twice a month) was greater than at 4 wk.

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68 The decline in CP in months when HMA was greater was attributed to dilution of CP across leaves. In general, CP and IVD D M of Mulato harvested in October were greater than that of forage harvested in August through to September. Herbage CP of Mulato was greater at 2 wk regardless of stubble height than for the 4 wk regrowth interval. Forage digestibility of Mu lato was greater at 2 than 4 wk regrowth interval through the clipping period except in October. Persistence There was no difference in persistence between the 2 and 4 wk defoliation treatments except at the 7.5 cm stubble height where the Mulato cover was greater at the 4 wk regrowth interval. Clipping Mulato below 2.5 cm at a regrowth interval of less than 2 wk would likely result in decreased persistence of less than 60% of the initial stand after 1 yr Implication s of the Research Animals grazin g Mulato pastures did not have greater animal performance despite Mulatos superior HM, HMA, and nutritive value than bahiagrass Considering the inputs and edaphic -climatic conditions of this study, Mulato should be grazed at a stocking rate of 8 heifers ha1 to optimize GHA and ADG. However, long -term studies should be conducted to evaluate the persistence of Mulato pastures grazed at this stocking rate for multiple years. B ecause Mulato was more negatively impacted by flooding conditions of the soil than bahiagrass Mulato should be planted in areas with well -drained soils A defoliation regime of 4 wk regrowth interval at a 7.5 cm stubble height is recommended for optimizing HMA of Mulato while maintaining the persistence of the stand There is potentia l for Mulato as an alternative forage for bahiagrass pastures in South Florida, however, future research on persistence of Mulato on varied soil moisture conditions and at different latitudes is needed to determine the adaptability of Mulato throughout Flo rida.

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69 APPENDIX DATA TABLE Table A 1. Weather data for Years 2007 and 2008 in Ona, FL. Month Rainfall Average temperature 2007 2008 65 yr 2007 2008 63 yr Average Average ---------------mm -------------------------o C -----------------Jan. 36.8 23.6 54.9 17.2 16.0 9.7 Feb. 51.3 39.9 66.8 15.4 18.3 10.3 Mar. 16.0 57.4 79.2 19.0 18.8 12.5 Apr. 41.9 7.9 63.0 20.1 20.0 14.4 May 10.4 71.1 94.7 23.2 24.1 17.4 June 206.0 253.2 220.7 25.2 25.3 20.6 July 154.4 198.1 212.6 26.2 25.8 21 .8 Aug. 210.8 254.0 209.6 27.0 26.3 22.1 Sep. 171.2 142.7 186.9 25.8 26.1 21.7 Oct. 52.3 41.9 78.0 24.8 22.2 18.2 Nov. 2.3 49.0 18.6 13.8 Dec. 52.6 51.1 18.7 10.7 Total 1006 1089.8 1366.5

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82 BIOGRAPHICAL SKETCH Uduak Ime Inyang was born in Lagos Nigeria. She received a Bachelor of Agriculture in a nimal science (2002) at the University of Benin, Benin City, Nigeria She t aught a griculture s c ience and m athematics for a year after graduation at Federal Government Girls College, Ezzamgbo, Ebonyi, Nigeria. In 2005, s he worked as a Consultant at Gas to Power Integrated Project, funded by World Bank in conjunction with the Federal G overnment of Ni geria. Uduak began her m asters program in a gronomy at the University of Florida, under the supervision of Dr. Ike Ezenwa of the Southwest Florida Research and Education Center, Immokalee in 2007 before his resign ation. Uduak moved to the Range Cattle Resea rch and Education Center, Ona, Florida to conduct her research on Brachiaria hybrid (Mulato) advised by Dr. Joao Vendramini in May 2007. She served as a Graduate Research Assistant from 2007 through 2009. Uduak hopes to pursue a doctoral program in Food and Resource Economics in the near future