Prediction of in situ protein degradability in the rumen. Results of a European ringtest

Abstract

Five samples of feeds (Soyabean meal, coconut meal, cottonseed meal, barley and fish meal) were analyzed by 23 laboratories representing 17 countries. The analyses made were crude protein, solubility of the protein measured on filter paper and the degradation of crude protein and dry matter using nylon bags incubated in the rumen of cows or sheep for different lengths of time (0, 2, 4, 8, 16, 24 and 48 hours). The mean protein degradabilities calculated by assuming a ruminal outflow rate of 8% h −1 were for soyabean meal, coconut meal, cottonseed meal, barley and fish meal, 63%, s.d. = 11.1; 47%, s.d. = 8.0; 51%, s.d. = 9.1; 72%, s.d. = 8.4 and 23%, s.d. = 5.5, respectively, which is comparable to what has been found in in vivo experiments with similar feeds. The variation between laboratories was considerable for all the analyses including the determination of crude protein contents of the feeds and solubilities of protein measured on filter paper. The variation between laboratories in the determination of protein degradability was mainly associated with differences between laboratories in the methods used for sample preparation and processing, and in the bags used for incubation. It was likely also influenced by the poor repeatabilities between laboratories in the determination of crude protein content and by the type of filter and nylon bag material used. It was to a lesser degree influenced by the rate of protein degradation in the different rumen environments. Greater emphasis should be given to calibration of the crude protein analysis in the different laboratories and to standardization of the procedures for measuring protein solubility on filter paper and protein disappearance from nylon bags.