Intake and digestion in swamp buffaloes and cattle. 2. The comparative response to urea supplements in animals fed tropical grasses

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Abstract
Swamp buffaloes (Bubalus bubalis) and crossbred cattle (B. indicusxB. taurus) were offered two forages in two experiments. In Expt 1, four animals of each species were offered mature Rhodes grass hay (Chloris gayana) with a mineral supplement or with a supplement of minerals and urea (17·6 gN/d). In Expt 2, another group of four buffaloes and four cattle were offered mature spear grass hay(Heteropogon contortus) with mineral supplementation at intervals of 3 h. Four levels of urea (0, 5, 21 and 97 g/day) and35S-sulphate were continuously infused in four periods.Rhodes grass was consumed in greater amounts by cattle, whereas buffaloes ate more spear grass. Urea supplements increased intake of Rhodes grass by 12% in buffaloes and 22% in cattle, and of spear grass by 34% in buffaloes and 41 % in cattle. Digestibility of cell wall constituents and acid-detergent fibre of spear grass was lower (P< 0·05) in buffaloes than in cattle (417v. 499; 471v. 560 g/kg respectively). In Expt 2, dry matter digestibility progressively increased (P< 0·05) from 364 to 408 g/kg with increased urea infusion. Rumen dry matter pool increased by 11–21 % on infusion of 97 g urea/day, compared with no urea. Digestion of ground forages incubatedin situin the rumen was depressed below rumen ammonia levels of 30–60 mg N/l, while digestion of cotton thread was depressed below 60–80 mg N/l (Expt 1) or 150–200 mg N/l (Expt 2).Patterns of N content in cotton thread suggested that more microbes attached in buffaloes and there was subsequently faster detachment than in cattle, particularly with increased urea infusion.