AbstvactRice straw was fed ad libitum to Indonesian Zebu (Ongole) and swamp buffalo bulls. The straw was fed either untreated or treated with 4 % NaOH for 24 h, and with or without a Leucaena (L, leucocephala) supplement. Elephant grass (Pennisetum puvpuveum) was fed as a control diet.Alkali treatment improved digestibility of dietary nutrients and the metabolizability of dietary energy, and was associated with an increase in the movement of water and digesta through the gut. However, it also depressed appetite by 25-30%, and this may have been related to the high pH of both the diet and the rumen following feeding. Intake of the alkali-treated rice straw, when fed with Leucaena, was increased by up to 30%, whereas that of untreated rice straw was depressed by 10-20%. In the Leucaena-supplemented animals, increases were observed in rate of passage of digesta, balances of dietary nutrients (nitrogen, phosphorus and calcium) and levels of rumen metabolites. The animals offered elephant grass had similar intakes to those of animals receiving untreated, unsupplemented rice straw.The Ongoles and buffaloes responded in a similar manner to the various dietary treatments and, apart from differences in water metabolism, urinary urea-nitrogen excretion and rate of passage of digesta, the nutritional physiology of the two animal species was very similar.

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