| Symbiosis between microbes and ruminants gives the animal a unique ability to digest fiber and transform it into meat, milk, power and other useful products. Manipulation of rumen ecology with selective antimicrobial compounds can have beneficial effects by altering microbial output, allowing the animal to achieve greater levels of production per unit of input. Two experiments were conducted to determine effects of antimicrobial compounds on in vitro fermentation with ruminal microbes in continuous culture. Inclusion of bismuth subsalicylate decreased (P < 0.05) organic matter digestion, volatile fatty acid production and had negative influences on nitrogen and fatty acid metabolism. Results indicate that bismuth subsalicylate at 0.5% of diet dry matter was detrimental to overall fermentation with rumen microbes, and lower dosage levels should be investigated. In experiment 2, beta extract from the hop plant (Humulus lupulus) was administered to continuous culture fermenters at 0, 600, 1200 or 1800 mg of beta acids / kg of dry matter. Inclusion of beta extract did not affect (P > 0.05) ingredient digestion, volatile fatty acid production or nitrogen metabolism. Beta extract tended (P = 0.09) to increase culture pH, however effects were modest and lower than biologically relevant values. Further research investigating the adaptation of microbial populations to hop beta extract was recommended. |
