EFFECT OF POSTWEANING AGE ON RATE OF IN-SITU PROTEIN DISAPPEARANCE IN CALVES WEANED AT 5 WEEKS OF AGE

Four rumen-cannulated calves were used in a block design to evaluate the in situ rate of protein disappearance in the rumen of soybean meal, heat-treated soybean meal, corn gluten feed, and corn distillers grains at 2, 4, and 8 wk after weaning. The rates of degradation of the four feeds also were evaluated in an in situ experiment using lactating cows and in an enzymatic in vitro experiment using Streptomyces griseus to determine whether the in vitro method could predict protein degradation in the rumen of calves. An interaction between protein source and age after weaning occurred for rate of CP disappearance. For soybean meal and corn gluten feed, the rate of disappearance of CP increased with age, but no age effect on rate of CP disappearance occurred for heat-treated soybean meal or distillers grains. Rates of CP disappearance between cows and calves were similar for distillers grains and com gluten feed, but no similarities existed between the in vitro and in situ methods. During the first 4 wk after weaning, feedstuffs high in degradable protein have lower rumen degradation rates than they do at 8 wk after weaning. Rumen degradation rates of low degradable proteins do not change during the first 8 wk after weaning. In addition, the cow in situ and in vitro methods were not suitable for prediction of rumen protein degradability of early weaned calves.