Some effects of starch on protein utilization by sheep

Abstract

1. One feeding experiment was carried out with seven adult rams (49–65 kg) and a second with eight young rams (39–51 kg) to compare the influence of starch supplementation on the utilization of protein; soya-bean meal was the main protein source in all diets. Cottonseed hulls and Rhodes hay served as energy sources in the basal diets. The energy content of the experimental groups (four adult or four young rams) was increased to 150% of that of the control groups by addition of crushed maize while the intake of digestible protein was equalized by adding maize gluten to control diets.2. Adult rams retained 20% more nitrogen and young rams 20% less nitrogen on the highenergy than on the control diet. The effect in young rams was not significant.3. Addition of maize to the diets was followed by a decrease in protein digestibility, but no parallel trend was found between protein digestibility and efficiency of nitrogen retention.4. In both experiments rumen ammonia and blood urea values were higher in sheep given the control diet than in those receiving the diet supplemented with maize.5. The dehydrogenase activity of rumen contents from young rams was only slightly raised by the maize supplement compared with the much larger increase that occurred in adult rams.6. The concentrations of total volatile fatty acids in the rumen contents of adult and young rams were not markedly influenced by the addition of maize to their diets but a slight increase in the concentrations of propionic and butyric acids and a decrease of the ratio of acetic to propionic acid occurred.