Protein sub-fractions and amino acid profiles of rumen-undegradable protein in dairy cows from soybean, cottonseed and fish meals

The aim of this study was to investigate the degradability and the amino acid content of the ruminal undegradable protein in dairy cows from soybean meal, cottonseed meal and fish meal. Three 600 kg ruminally fistulated Holstein dry dairy cows were used for in situ incubations. The rumen protein degradability of soybean meal, fish meal and cottonseed meal at rumen outflow rate of 8% were 63.47, 37.71 and 82.10%, respectively. From the SDS-PAGE pattern and densitometric scanning, the basic sub-unit of glycinin in soybean meal, as well as most sub-fractions of fish meal protein were not completely degraded after 24 h incubation, whereas the protein of cottonseed meal was almost completely degraded. However, the in vitro digestibility of the undegradable protein from soybean meal and fish meal were higher than that from cottonseed meal. In addition, the amino acid content of the ruminal undegraded proteins differs from that of the original feed consumed by cows.