Protein evaluation in ruminants. 2. Evaluation of agroindustrial by-product-based rations in metabolic and rumen studies of buffalo calves

Abstract

Six growing male buffalo calves fitted with a rumen fistula were fed a 40% wheat straw and 60% concentrate mixture containing urea (basal diet), groundnut cake (GNC), mustard cake (MC), cottonseed cake (CSC), guar meal (GM) or sun-dried poultry excreta (PE) as a supplementary protein source in a 6 × 6 Latin square design. The dry matter intake was kept constant for all the diets. Six metabolic trials were conducted while allowing the switch over every 32nd day. After every trial, rumen liquor samples were collected for 3 consecutive days at 0, 1, 2, 4 and 6 h after feeding. There was no difference ( P < 0.05) in the crude protein digestibility of isonitrogenous diets based on different natural protein sources, i.e. GNC, MC, CSC and GM. The crude fibre digestibility was not affected by the different protein supplements ( P < 0.05) although it appeared to be less with the supplementation of CSC. The crude fat digestibility was found to be more ( P < 0.05) on oilseed cake diet compared with the GM, PE and basal diets. Urinary-N excretion was significantly higher with the GNC diet and less with the GM and PE diets compared with the MC and CSC diets. The mean pH of the strained rumen liquor (SRL) was almost the same on the test diets (7.28–7.33), but was significantly less ( P < 0.05) for the basal diet (7.20). An increase in the total-N (mg per 100 ml SRL) concentration observed at 1 h postfeeding was least for the GM diet and maximum for the GNC and CSC diets, whereas the mean level of total-N from GNC, MC and GM did not differ significantly ( P < 0.05) from one diet to another (110.2, 105.2 and 109.2 mg per 100 ml SRL). Also, in the case of GM, there was a slow decline in N concentration at 2 and 4 h postfeeding compared with GNC and MC. The protein-N concentration (measured as TCA-N) (trichloroacetic acid precipitate-N) ranged from 53.7 to 66.0 mg per 100 ml SRL and the differences between various protein sources were significant ( P < 0.05). The higher level of the non-protein-N fraction in the SRL for the GM and PE diets observed at 4 h postfeeding was attributed to the higher level of amino-N. The mean NH 3-N concentration ranged from 22.4 to 35.6 mg per 100 ml SRL and was significantly higher for the diet at all times. It appeared that the rate of release of NH 3 for GNC was more than its incorporation into microbial protein, thereby resulting into its net loss via the urine. The results also indicated that GM protein degradation was of a continuous nature which encouraged greater utilization of NH 3-N for the synthesis of microbial-N.