The Estimation of Feed Protein Degradability in the Rumen Using Nylon Bag, Microbial Labelling (s) and Plant Labelling (n) Techniques

Three techniques for estimating rumen protein degradability were used together with in vivo apparent nitrogen digestibility estimates from sheep fed dried chopped Pangola grass or Siratro. The techniques used were 1) nitrogen disappearance from nylon bags suspended in the rumen, 2) S labelling of rumen microbial protein with plant nitrogen degradability calculated as the difference between microbial and total non-ammonia nitrogen flows, using a correction for endogenous nitrogen, and 3) N labelled plant protein incorporating an endogenous nitrogen determination. Significant differences (P < 0.05) between the two feeds for rumen protein degradability estimates were shown for all three techniques. The nylon bag technique gave significantly higher estimates of protein degradability for Siratro (79.6%) compared with Pangola grass (68.3%), but for the two isotope techniques, Panola grass was of higher degradability than Siratro. estimated from 35S Degradability labelling gave significantly lower estimates (91.5% Pangola, 79.6 Siratro) than those determined by the N plant labelled technique (98.6%) Pangola, 95.5% Siratro).