Rumen escape protein in concentrate ingredients determined with the nylon bag and enzymatic techniques

Rumen escape protein (REP) was determined for 26 concentrate feed ingredients using the nylon bag technique and in vitro using a proteolytic enzyme preparation of Streptomyces griseus. In vitro, the samples were incubated for 0, 1, 6 and 24 h. The highest correlation was observed between percentage REP (%REP), determined with the nylon bag technique, and the in vitro undegradable fraction after 1 h of incubation (%U1) (R2=0.77). Longer incubation times weakened the relationship. %REP could be estimated from %U1 according to: %REP=−0.76 (±5.99)+0.81 (±0.09)×%U1. The 0 h incubation, representing in vitro solubility, had a relationship (R2=0.67) with in situ %REP, suggesting that %REP is mainly determined by crude protein (CP) solubility and to a lesser extent by degradation.