Rumen fermentation, bacterial and total volatile fatty acid (TVFA) production rates in cattle fed on urea-molasses-mineral block licks supplement

Of twenty rumen fistulated calves, four were allocated randomly to each of five tests. Animals were offered only wheat straw ad lib (T-1), or in addition were supplemented with concentrate mixture (T-2), or any one of three different types of UMMB-lick type A (T-3), type B (T-4) and type C (T-5). A metabolism trial was conducted. Bacterial production rate (BPR) and total volatile fatty acid (VFA) production rate were estimated with an isotope dilution technique using S-35 sodium sulfate and C-14 sodium acetate, respectively. Nitrogen (N) balance in T-1 animals were negative but, positive in other treatment groups. Total-N, ammonia-N, non-protein-N, TCA-precipitable-N in rumen on treatment groups T-3 to T-5 were comparable with T-2 but higher than T-1 (P < 0.01). Ammonia levels in rumen improved significantly on UMMB supplementation. Bacterial pool size and BPR were improved three-fold (P < 0.01) in T-2 to T-5 in comparison with T-1. BPR per unit of digestible organic matter intake was higher on UMMB-lick type B and C than type A. Total VFA concentration, production rate and molar proportion of individual VFAs were higher (P < 0.01) and acetate to propionate ratio as well as non-glucogenic ratio were lower (P < 0.01) on treatment groups T-3, T-4 and T-5 than on T-1, while comparable with T-2. Y-ATP (gram of bacteria per mole of ATP) was 5.7, 8.9, 7.4, 9.7 and 9.6 in T-1 to T-5, respectively. Nitrogen incorporation efficiency by rumen bacteria was lower (P < 0.01) on supplementation of UMMB-licks compared to concentrate supplement. In conclusion, it would be possible for synergy in N and energy availability from UMMB-lick supplementation to wheat straw to stimulate microbial yield and fermentation in rumen like that from conventional concentrate supplement. The composition of UMMB-lick type B and type C was found to be better than type A in improving the microbial yield. (C) 1997 Elsevier Science B.V.