Effect of supplementation with different proportions of barley grain or citrus pulp on the digestive utilization of ammonia-treated straw by sheep

The effect of carbohydrate supplementation on rumen utilization of ammonia-treated straw was studied in four rumen-cannulated ewes (42.0 (s.e. 2.80) kg live weight) in a Latin-square design. Diets were a 50 : 50 mixture of ammoniated barley straw and a concentrate made up with different ratios of barley grain and citrus pulp, namely M1 (100 : 0), M2 (66 : 33), M3 (33 : 66) and M4 (0 : 100). Concentrates also included soya-bean meal and urea to make diets isonitrogenous. Diets were given in one meal in the morning at 0.8 kg/day. There were no significant differences among treatments in daily weighted means of rumen pH and concentration of volatile fatty acids. Acetate, propionate and butyrate molar proportions were not different among treatments, but proportions of isobutyrate (P < 0.05) and isovalerate (P < 0.10) were higher for M1 and M2. Ammonia concentration immediately before feeding was lower (P < 0.05) for M3 and M4 (72.1 and 51.3 mg/l) than for M1 and M2 (97.0 and 107.9 mg/l). Total rumen bacterial concentration was higher (P < 0.05) with the highest barley proportion, whereas enzymatic activity against structural carbohydrates of particle-associated bacteria did not differ significantly among treatments. Digestibility of neutral-detergent fibre increased (P < 0.05) with the increase in the proportion of citrus pulp in the concentrate (0.647, 0.674, 0.684 and 0.693 for M1, M2, M3 and M4; s.e. = 0.0086). Urinary excretion of purine derivatives decreased linearly (P < 0.05) as the proportion of citrus pulp in the diet increased, while faecal excretion of purine bases was not significantly affected by dietary treatments.