The influence of poultry waste and other nitrogen sources upon carbohydrate fermentation in vitro and glucose metabolism in vivo in sheep
Experiments were conducted to investigate the comparative effects of the nitrogen sources, poultry waste, urea or casein/fish meal on the microbial fermentation of carbohydrates in vitro and on in vivo glucose metabolism in sheep. In vitro studies An artificial rumen designed by Czerkawski and Breckenridge (1969) was used in the present study. A series of short term incubations were carried out in which starch or cellulose was incubated with casein, urea, poultry waste or casein + urea. These food combinations were isonitrogenous and had identical dry matter contents. An additional treatment containing grass cubes, hay and poultry waste was also studied. Control incubations were carried out in parallel with all treatment incubations. Nutrients used in control incubations were grass cubes and hay. The duration of each incubation was 61/2h. Fermentation parameters studied were, rate of gas production, pH, and concentrations of volatile fatty acids and ammonia. The fermentation of poultry waste with either of the carbohydrate sources gave rise to a higher volume of gas production than either casein or urea. Urea resulted in a reduction in the volume of gas in the incubation vessels and caused a much larger increase in pH of the incubation medium than did poultry waste. Using mixtures based on starch, the total gas produced in the medium containing poultry waste after 60 and 390 min. of incubation was 44% and 100% greater respectively than that produced from the medium containing casein. Similarly when poultry waste was fermented with cellulose, the total gas production after 60 and 390 min. was 59% and 108% greater respectively than that produced from the fermentation of cellulose + casein. The differences in gas production between urea and poultry waste or urea and casein were not quantified since urea resulted in a reduction in the volume of gas produced. From the starch and cellulose based diets, VFA production in the presence of poultry waste was greater than that from either casein or urea. At the end of incubation, production of VFA from the fermentation of starch + poultry waste was 1.5 or 3.5 times greater than that from starch + casein or starch + urea respectively. Similarly, for a mixture containing cellulose, VFA production in the presence of poultry waste was 2.3 or 6 times higher than that derived from casein or urea respectively. With both starch and cellulose, poultry waste maintained much lower concentrations of ammonia and much lower levels of pH than did urea but considerably higher than those observed with casein. Incubation of grass cubes and hay with poultry waste resulted in greater production of gas and VFA than that obtained from the controls (grass cubes and hay). In vivo studies The primed-continuous infusion technique of Steele et al. (1956) was used to study the comparative effects of poultry waste, urea or fish meal on glucose metabolism with 3 sheep using a 3 x 3 Latin square design. The animals were frequently fed during the experimental period and were maintained on medium quality high roughage diets. Although there were no significant changes in blood glucose level in sheep receiving different nitrogen supplements, the urea and poultry waste containing diets showed a tendency to give lower values than did the fish meal diet. Similarly overall mean insulin concentrations tended to be higher for the fish meal diet than those for the poultry waste or urea diet. Plasma levels of free fatty acid showed small differences between diets which were not significant. Irreversible loss of glucose, glucose pool size, glucose space were estimated. In three out of nine infusions plateau specific activity of glucose was achieved. Consequently, these parameters were calculated for two animals only on each of the dietary treatments. When a plateau glucose specific activity was not attained, the animals exhibited irregular feeding behaviour after about 3h. of infusion and blood analysis showed that they had unusually high levels of cortisol. Plasma glucose concentrations of these animals throughout the infusion period, varied considerably. It appears that uneven feeding behaviour resulted in large fluctuations in the plasma glucose concentrations and specific activity. The results of the in vitro study indicated that poultry waste is more efficient in promoting the utilization of both starch and cellulose than either urea or casein. Poultry waste also caused an improvement in the overall digestion of natural roughage feeds. It was not possible to draw firm conclusion on the results of in vivo experiments because, of the variable data. No significant differences were observed in the concentrations of plasma glucose, insulin, urea or free fatty acids between dietary treatments of fish meal, urea or poultry waste.