Influence of rumen ammonia concentration on the rumen degradation rates of barley and maize.

Four rumen-cannulated steers were given barley and maize diets supplemented with graded levels of an ammonium acetate solution. Animals were fed hourly from automatic feeders and water consumption was controlled to achieve steady-state conditions in the rumen. Dacron bags containing rolled barley or ground barley were incubated in the rumen of barley-fed steers, while ground maize and autoclaved maize were incubated in the rumen of maize-fed steers. Fractional degradation rates of dry matter were estimated for each cereal substrate incubated using a single-pol exponential decay model. No differences in degradation rate due to the method of feed processing were detected; however, barley was degraded at a faster rate than maize. Furthermore, the minimum rumen ammonia-nitrogen concentration required to maximize the degradation rate of barley (125 mg/l) was greater than that required to maximize the degradation rate of maize (61 mg/l). These results indicate that the optimal NH3-N concentration required to maximize the rate of grain digestion in the rumen is influenced by the chemical or structural characteristics of the grain.