In vitro protein degradation of feeds using concentrated enzymes extracted from rumen contents

A method was developed and evaluated to measure protein degradation of feeds using proteolytic enzymes extracted from rumen contents. Strained rumen fluid was centrifuged and the pellet was extracted with butanol and acetone. Enzymes were then solubilized from the residue in water, and frozen for later use. Feed protein was degraded by incubating feeds with enzyme at 38°C. At the end of the degradation period, trichloroacetic acid was added to precipitate undigested protein. The final enzyme preparation maintained 62% of the proteolytic activity on azocasein of the original rumen fluid (plus rinse of solids). When enzyme was incubated at 38°C, activity on azocasein decreased slightly for 12 h and then increased. There was no difference between 3, 5 or 10 ml of enzyme on degradation of soya bean meal or lucerne hay protein at 6 or 16 h. This suggests that enzyme was supplied in excess for the duration of the incubation. Soya bean meal protein degraded at 0.15 h−1 for the first 2 h and slowed to 0.01 h−1 from 8 to 24 h. Similarly, lucerne hay protein degraded at 0.06 h−1 for the first 2 h and then slowed to 0.01 h−1. Degradation of feed protein was less than that measured using live microbes in a previous study. The method is simple with low variation within treatment, and enzyme activity appeared to be supplied in excess for extended incubations, but it appears that some requirements for long-term (> 2 h) protein degradation have not been met.