Effect of inoculum preparation and dietary energy on microbial numbers and rumen protein degradation activity

Chilling of whole rumen contents prior to preparation of strained rumen fluid enriched with particle-associated microorganisms resulted in rumen inoculum with the highest microbial dry weight, total bacterial counts, and degradation rates for casein and soybean meal. Strained rumen fluid, whole rumen contents blended with strained rumen fluid, chilled strained rumen fluid, and strained rumen fluid plus particle-associated microorganisms were lower in bacterial counts and microbial dry weight. Except for strained rumen fluid plus particle-associated microorganisms, protein degradation rates were also lower. Three ruminally cannulated cows were used in a 3 X 3 Latin square experiment to determine the effect of diet on rumen microbial numbers and protein degradation rates. Cows were fed the following diets ad libitum: 1) 100% alfalfa hay (20.7% crude protein); 2) 63% alfalfa hay and 37% corn-soybean meal concentrate (18.2% crude protein); and 3) 37% alfalfa hay and 63% corn-soybean meal concentrate (15.1% crude protein). Diet 3 yielded rumen contents with the highest concentration of microbial dry weight, total and viable bacterial counts, total protozoal counts, and fractional degradation rates for casein and bovine serum albumin. However, degradation rate per unit microbial dry matter was not altered by diet.