Rumen escape protein in grass and grass silage determined with a nylon bag and an enzymatic technique

Rumen escape protein (REP) was determined for six grasses and 16 grass silages using a nylon bag technique and an in vitro technique using a proteolytic enzyme preparation of Streptomyces griseus. In vitro, the samples were incubated for 0, 1, 6 and 24 h. The highest correlation observed between percentage REP (%REP), determined with the nylon bag technique, and the in vitro undegradable fraction (U) occurred at 24 h of incubation (%U24; R2=0.71). Shorter incubation periods weakened the relationship (R2=0.46–0.59). Percentage REP could be estimated from %U24 as %REP=3.3 (±4.02) + 1.31 (±0.19) ∗%U24. For the incubation periods investigated, results show that the highest relationship with %REP occurred with an incubation period of 24 h for these grass and grass silage samples.