The Nutritive Value of Tropical Pastures for Grazing Cattle PDF Download

Author: Luiz Carlos Lopes Freire
Publisher:
ISBN:
Category : Animal nutrition
Languages : en
Pages : 346

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Book Description
The present study describes experiments aimed at manipulating and evaluating the nutritive value of tropical pastures for grazing cattle. Before commencing experiments with grazing cattle, an experiment was conducted with sheep to determine whether the digestion of mature tropical grass forage varied appreciably from that expected from temperate grass of similar composition. Results from this experiment indicated that despite the low intake and digestibility of mature tropical grass, the digestible fraction of this forage behaved in ways predicted from published data obtained with temperate species. It was concluded that principles of rumen function and ruminant nutrition established with temperate forage species could validly be applied to tropical forage species. The subsequent experiment was aimed at avaluating the effects of superphosphate fertiliser on the botanical and chemical composition and nutritive value of the diet selected by cattle grazing Stylosanthes-native grass pastures. The data obtained in this experiment showed that superphosphate fertiliser improved the nutritive value of the diet selected. Animals grazing fertilised pastures had a significantly higher organic matter intake than those grazing unfertilised pastures during the wet and dry seasons but not during the wet-dry transition. This lower consumption with unfertilised pastures during the wet and dry seasons was associated with lower digestibility of the diet selected and possibly also with lower phosphorus content during the wet season. There was no evidence that higher organic matter intake observed for fertilised pastures was associated with a greater production of legume nor with the ingestion of a greater proportion of legume in total diet. It appears that the amount of legume in the diet was mainly determined by the time of the year and by the proportion of legume available in the pasture. Three experiments were conducted to evaluate the use of monensin sodium for manipulating rumen fermentation on the nutritive value of native pasture. The first experiment studied the effect of monensin on liveweight change of steers grazing a native pasture and the second examined this effect on the nutritive value of the forage selected during the wet and dry seasons, while the third used penned animals to study the effect of monensin on the nutritive value and utilisation of native pasture hay with and without nitrogen supplements. Results from these experiments indicated that monensin was efficient in changing the rumen fermentation patterns by increasing the production of propionic acid and reducing acetic and butyric acids. However, no beneficial effects on intake and liveweight gain of grazing animals was observed by the use of monensin during the wet or dry season. Although supplementation of the low quality hay with urea plus formaldehyde-treated casein produced an increase in the digestible organic matter intake (largely by improving both intake and digestibility), no benefit for the animal was achieved by the use of monensin. Comparisons made between predicted and observed liveweight gain of cattle grazing tropical pastures suggest that liveweight gain could accurately predicted from digestible organic matter intake by the use of tables presented by the Commonwealth Agricultural Bureaux - CAB (1980). However, estimates of feed consumption from formulae presented by the CAB underestimated the observed intakes by 25% during the wet season. There is, therefore, an urgent need for the development of equations that would allow the estimation of the digestible organic matter intake. A relationship between organic matter digestibility and digestible organic matter intake is proposed and its limitations are discussed. Although it is clear that much research is needed to elucidate problems of nutrition of cattle grazing tropical pastures, the results from this investigation suggest that the CAB system does provide a useful framework to base the development of system for livestock feeding for tropical as well as for temperate Australia.