The effect of protein supplements varying in degradability on the intake and utilization of poor-quality roughages
A series of experiments were conducted to study the effect of protein or non-protein supplementation on the intake and utilization of poor-quality roughages. 1. In the first experiment an estimate of the rate and extent of degradation of soyabean meal, heat-treated soyabean meal, formaldehyde-treated soyabean meal and fishmeal was measured in sacco. The proteins were incubated in the rumen of cows receiving high roughage diets. A highly positive correlation was observed between the nitrogen (N) and the dry matter (DM) disappearance. A highly significant (P < 0.001) difference in N disappearance between the different proteins was observed. Soyabean meal was highly degraded, fishmeal was less degraded but had the highest N loss during the first few hours, whereas the treated proteins were least degraded. The N disappearance was significantly (P < 0.001) affected by the basal diet given to the animals. Using a mathematical model, degradability values for these proteins were calculated. The amino, acid composition and the acid-pepsin digestibility of N of the residues left in the bags indicated little variation in composition and nutritive value from the original protein. In the second experiment, the proportion of undegraded dietary protein and the microbial protein entering the small intestine were studied in vivo in duodenally fistulated sheep. Poor-quality chopped hay (B) or chopped hay with isonitrogenous supplements of urea (BU), soyabean meal (BS) or fishmeal (BF) were used. Ru-P and Cr-EDTA were used as digesta markers, and 35S was used as a microbial marker. Very low nitrogen flow rates were observed for all diets. The microbial protein synthesis was 4.9, 6.7, 4.9 and 8.7 g, N/kg FOM for diets E3, BU, BS and BF respectively. High rumen degradabiIity values of 0.78, 0.97, 0.95 and 0.87 were calculated for the respective diets. 2. Two experiments were carried out with steers to study the intake of barley straw and low quality hay supplemented with urea and/or fishmeal. The urea was offered either with a concentrate supplement of rolled barley or sprayed on to the roughage. Fishmeal supplementation increased the voluntary intake of both roughages and was superior to urea. Urea was more beneficial when mixed with the concentrate supplement rather than when sprayed on the hay. 3. To investigate further the intake of poor-quality roughages, growing steers lighter in weight than those used in the previous experiments were used in three experiments. The basal energy supplement in these experiments was a mixture of tapioca and molasses. In Experiment Five long barley straw was offered with nitrogen supplements of urea, soyabean meal and fishmeal/urea. The diets provided different amounts of rumen degradable protein (RDP) and undegradable protein (UDP). The experiment was supported by a digestibility trial. There were no significant differences in the DM intake of straw between the treatments. There was no response to any extra RDP or UDP. In Experiments Six and Seven the barley straw was treated with aqueous ammonia and offered in long form. The effect of three amounts of RDP on the intake of the treated straw was studied in Experiment Six using urea as the nitrogen supplement in two treatments. The daily intake of the treated straw was highest from the treatment which had no urea and a lower RDP than the suggested requirements. The high urea diet which supplied excess of RDP resulted in the1 lowest intake of ammonia-treated straw. The response in liveweight gain of growing steers given ammonia- treated straw with a nitrogen source of a low degradability was studied in Experiment Seven. Two amounts of UDF supplied by fishmeal were used with two energy levels. The results showed a clear response in liveweight gain to additional UDP at both energy levels. However, the actual liveweight gains were less than the predicted gains.