Ruminal fermentation pattern, bacterial population and ruminal degradation of feed ingredients as influenced by ruminal ammonia concentration

The effects of ruminal ammonia concentration on bacterial numbers, fermentation pattern and degradation of feed ingredients in the rumen were examined with three nonlactating Holstein cows fitted with ruminal cannulas. Cows were fed twice daily a complete mixed diet (90% whole plant oat silage and 10% concentrate mixture) containing 11.1% CP on a DM basis. Ammonium bicarbonate (NH4HCO3) was infused continuously into the rumen at levels of 0, 95, 190 or 280 g/d. Infusion of NH4HCO3 linearly increased (P less than .05) the concentrations of ruminal ammonia and blood urea N. Total VFA concentrations and mixed bacterial numbers also were increased (P less than .05) by NH4HCO3 infusion. Infusions of NH4HCO3 increased (P less than .05) butyrate and decreased (P less than .05) isobutyrate and isovalerate proportions. Infusion of NH4HCO3 increased (P less than .05) rate of degradation of soybean meal DM but did not (P greater than .05) influence degradation characteristics of fish meal and barley grain. In conclusion, supplementation of N by continuous infusion of NH4HCO3 appeared to stimulate bacterial growth and fermentation but it did not influence extent of ruminal degradation of selected feed ingredients.