Degradability of forage proteins by in situ and in vitro enzymatic methods

The overall objective of these two studies was to evaluate the efficacy of using the proteolytic enzyme from Streptomyces griseus to estimate concentr ations of ruminally degradable protein (RDP) in a wide array of forages. In the first study, alfalfa and prairie bays that previously had been evaluat ed in vivo for RDP were incubated in a replicated 3 x 3 factorial combinati on of enzyme concentrations (6.6, 0.66, and 0.066 activity units/ml of incu bation medium) and incubation times (2, 4, and 48 h). Two treatment combina tions (6.6 activity units for 4 h and 0.066 activity units for 48 h) yielde d respective RDP estimates for alfalfa and prairie hay that were close to t he known in vivo values. In the second study, 20 diverse forages were evalu ated for RDP by using the in situ technique. These forages also were evalua ted for RDP with the two enzyme concentrations identified in the first stud y, but incubation times were expanded to include 1, 2, 3, 4, and 5 h at the high concentration and 24, 30, 36, 42, 48, and 54 h at the low concentrati on. At the high enzyme concentration, r(2) statistics from linear regressio ns of enzymatic estimates of RDP on corresponding estimates obtained by the in situ procedure were high (r(2) greater than or equal to 0.898) at all i ncubation times; in addition, slopes (range = 0.88 to 1.00) and intercepts (range = -9.4 to 3.5%) approached unity and 0, respectively. At the lower e nzyme concentration, r(2) statistics were still good (>0.81), but slopes (0 .59 to 0.67) and intercepts (18.5 to 21.9%) for all incubation times did no t meet the respective goals of unity and 0.