Ruminal degradation of crude protein in feedstuff – comparison of two methods

The rate of ruminal degradation of crude protein of feedstuff is important in order to estimate the amount of absorbable protein available in the intestine. In many countries the in sacco method is well accepted as a reference. However, this method is time-consuming and requires ruminal fistulated animals. Therefore, great efforts are undertaken to establish simpler in vitro methods which could facilitate the estimation of the protein value in feeds for ruminants. In the present study 17 commercial dairy compound feeds were used to investigate their ruminal crude protein degradation both by the in sacco and an in vitro method using two enzymes (cellulase and protease). Among the two methods only small differences in the calculated amount of absorbable protein occurred resulting from a good relationship between the in sacco and in vitro method (R2  = 0.86). However, before the enzymatic method developed by the RAP can be recommended for routine analyses further research is needed to clarify the effect of various factors such as the content of protein and other nutrients of the feedstuff on its accuracy.