Manipulation of the rumen fermentation and its effects on digestive physiology
The aims of the present study were to determine the effects of various forms of rumen manipulation on rumen fermentation, blood metabolites and circulating gastrointestinal hormones in ruminants, and to assess any post-ruminal effects of manipulating agents. The mechanism of gut hormone release in steers fed by intragastric infusion was also examined. A long term study of defaunation in sheep indicated that a steady state was reached six months after defaunation. Whereas at the end of this period ruminal concentrations of end products of rumen fermentation and blood metabolites were similar in both faunated and defaunated animals, after only one month defaunated animals had lower rumen ammonia and blood urea concentrations than their faunated counterparts. In general the plasma concentrations of the gastrointestinal hormones gastrin and CCK remained similar between faunated and defaunated animals, although the gastrin concentration in defaunated sheep increased at one year when compared to six months after defaunation. In steers the reintroduction of protozoa increased blood glucose, which increase plasma insulin secretion. The addition of the fungal feed additive, Aspergillus oryzae increased the viable count of bacteria and the molar proportion of propionate in the rumen of sheep, but did not alter gut hormones or blood metabolites. The inclusion of Saccharomyces cerevisiae fermentation extract, monensin and their combination altered rumen fermentation and microbial populations in both sheep and bulls, but gastrointestinal hormones and blood metabolites remained unchanged. Post-ruminal infusion of yeast culture had no effect on either gastrointestinal hormones or blood metabolites. However, post-ruminal infusion of monensin increased gastrin and blood urea concentrations, suggesting a post-ruminal role of monensin in nitrogen recycling. In the current study rumen manipulations likely to affect both the supply of protein from the rumen and the end products of rumen fermentation had no significant effects on hormonal secretion. The pattern of gastrin and insulin stimulation by protein and protein breakdown products in steers fed by intragastric infusions indicated that the stimulation of these hormones by luminal contents is different in ruminants compared with monogastric animals.