Paper-Lecture26 - I N VITRO F IBRE DIGESTION ASSOCIATIVE EFFECTS IN TROPICAL GRASS-LEGUME M IXTURES W.F BROWN Z.Q LAI 1 and W.D PITMAN Agricultural

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IN VITRO FIBRE DIGESTION: ASSOCIATIVE EFFECTS IN TROPICAL GRASS-LEGUME MIXTURES W.F. BROWN, Z.Q. LAI and W.D. PITMAN 1 Agricultural Research and Education Center, University of Florida, Ona Florida, U.S.A. _______________________________ Correspondence: Dr. W.F. Brown, Agricultural Research and Education Center, Route 1 Box 62, Ona FL 33865, USA. Present address: Guangxi Animal Science Research Institute, Nanning, 1 Guangxi, Peoples Republic of China. Abbreviated title: Associative effects in grass-legume mixtures. In Vitro Fibre Digestion: Associative Effects in Tropical Grass-Legume Mixtures 1 Abstract 2 This research evaluated the effects of source of ruminal fluid inoculum 3 and grass:legume proportion on the kinetics of in vitro neutral detergent
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1 fibre (NDF) digestion in grass-legume mixtures. Species used were the 2 grasses, bahiagrass ( Paspalum notatum ) and limpograss ( Hemarthria altissima ), 3 and the legumes, aeschynomene ( Aeschynomene americana ) and hairy indigo 4( Indigofera hirsuta ). Sources of ruminal fluid were from steers fed 5 limpograss hay (6.0 g/kg N) alone, or limpograss hay supplemented with urea or 6 cottenseed meal. 7 In vitro NDF digestion of 100% grass was greater when ruminal fluid from 8 steers fed limpograss hay plus supplemental N was used than ruminal fluid from 9 steers fed limpograss hay only. This suggested that activity of ruminal 10 microorganisms from steers fed limpograss hay only was limited in N and/or 11 other factors necessary for optimal in vitro fibre digestion. When ruminal 12 fluid from steers fed limpograss hay only was used, mixtures of aeschynomene 13 with either grass resulted in NDF digestion values that were greater 14 than the weighted average of NDF digestion values of the individual 15 forages. The magnitude of these increases were similar to the improvement in 16 NDF digestion of pure grass obtained using ruminal fluid from steers 17 fed limpograss hay plus supplemental N, suggesting that aeschynomene provided 18 soluble and/or degradable N to the fermentation. The likely mode of 19 action of the positive associative effects on NDF digestion was a 20 reduced lag time for the initiation of fibre digestion. 21 22 23 Introduction 24 Low crude protein concentration and high indigestible fibre content of 25 many tropical grasses have been related to reduced voluntary intake (Milford 26 and Minson 1965) and animal performance (Minson and Milford 1967), resulting 27 in low production levels or costly supplemental feeding. Input costs for 28 providing adequate nutrient supply to ruminants on low-quality forage-based 29 diets might better be directed at improving forage utilization rather than for 30 supplemental feed. 31 Incorporation of legumes into tropical grass pastures has been used to 32 improve the nutritional status of ruminants above that obtained with grass 33 alone. However, little is known about specific benefits of individual
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3 1 legumes, or ranges in nutritional improvement with legumes of varying quality 2 attributes. In low-protein (less than 70 g/kg crude protein) forage-based 3
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This note was uploaded on 09/19/2011 for the course ANS 5446 taught by Professor Brown during the Spring '08 term at University of Florida.

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Paper-Lecture26 - I N VITRO F IBRE DIGESTION ASSOCIATIVE EFFECTS IN TROPICAL GRASS-LEGUME M IXTURES W.F BROWN Z.Q LAI 1 and W.D PITMAN Agricultural

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