Effect of a controlled-release urea supplementation on feed intake, digestibility, nitrogen balance and ruminal kinetics of sheep fed low quality tropical forage

Four ruminally cannulated crossbred sheep (25 +/- 3.3 kg BW) were divided into a 4 x 4 Latin square design to measure the effects of controlled-release urea supplement (CRUS). The basal diet consisted of 60% sugar cane tops (Saccharum officinarum), 30% full plant corn stubble (Zea mays), and 10% King grass (Pennisetum purpureum). Feed intake, digestibility, N balance and in situ ruminal kinetics were studied with four diets, D1 (control), D2, D3 and D4, which included the ratios of 100:0%, 90:10%, 80:20% or 70:30% of basal diet with CRUS. Results showed DMI differences (P < 0.05) for D4 (822 g per day) versus D1, D2 and D3 (580, 659 and 700 g per day, respectively). N retention increased (P < 0.05) for D4 (35.69 g per day) versus D1, D2 and D3 (9.29, 6.85 and 19.10 g per day, respectively). In vivo N digestibility was greater (P < 0.05) in D4 (79.63%) than in D1 (57.57%). In vivo digestibility of DM, OM, GE, cellulose and hemicellulose was similar among the four groups. Digestibility of cell walls in D4 was higher (P < 0.05) at 74.06% versus 67.78% in D1. In situ DM digestibility showed differences (P < 0.05) among all diets at 9, 12, 24 and 48 h of incubation. Potentially digestible fiber, 52.61%, was higher (P < 0.05) in D4 versus 31.00% in D1. Indigestible fiber, 35.29%, was lowest (P < 0.05) in D4 compared to 81.51% in D1, Digestion rate constant (kd) was different (P < 0.05) between the experimental diets and control. Passage constant (k(p)) was different (P < 0.05) between all diets (0.036/h in D4 to 0.081/h in D1). True digestibility was higher (P < 0.05) in D4 (44.64%) compared to D1 (19.55%), but in D2 (24.54%) and D3 (28.22%) there was no difference. Cellulose in situ digestion rate, the potentially digestible fiber, was higher (P < 0.05) in D3 (42.74%) as compared to D1 (22.50%). Time of disappearance of cellulose in D4 (14.79 h) was less (P < 0.05) than in D1 (24.03 h), however there was no difference between D1 and D2. Hemicellulose in situ digestion was different (P < 0.05) between D3 (45.48%) and D1 (23.61%). Digestion rate was higher (P < 0.05) between D3 and DI as compared to D1. Passage rate was different (P < 0.05) between D4 (0.033/h) and D1 (0.018/h). True digestibility in D3 (34.84%) and D4 (34.62%) was higher (P < 0.05) than that in D1 (20.06%) and D2 (25.86%), Half-time disappearance (t(1/2)) for hemicellulose was higher (P < 0.05) in D1 (62.36 h) than in D3 (28.00 h) and D4 (20.64 h). This study demonstrated that low quality forages at 70% of the total diet can be efficiently utilized by sheep when controlled-release urea supplementation is 30% of the feeding regime. (C) 2001 Published by Elsevier Science B.V.