IN-VITRO DETERMINATION OF RUMINAL PROTEIN DEGRADABILITY OF ALFALFA AND PRAIRIE HAY VIA A COMMERCIAL PROTEASE IN THE PRESENCE OR ABSENCE OF CELLULASE OR DRISELASE

Ruminal protein degradation of alfalfa (2.62% N, 49.6% NDF, and in viv o undegradable intake protein [UIP] = 16.4% of CP) and prairie hay (.8 8% N, 69.4% NDF, and in vivo UIP = 44.5% of CP) was estimated using th e Streptomyces griseus protease (SGP) in vitro method with or without pretreatment with two carbohydrases: cellulase from Penicillium funicu losum or driselase from Basidiomycetes. Driselase is a broad-spectrum carbohydrase. Incubating forage samples for 48 h with cellulase or dri selase at a concentration of 800 mg/g per g of hay nearly maximized AD F and NDF disappearances. This concentration and incubation time then were used to pretreat hay samples. A 2-h pretreatment was included to evaluate the potential for reducing the analysis time. Other sets of s amples were or were not pretreated with acetate buffer alone. Followin g pretreatment, samples were subjected to SGP for .25, .5, 1, 2, 4, 8, 12, 24, and 48 h. Pretreatment altered the sizes of protein pools and their degradation rates. When the UIP contents of the forages were es timated using SGP and a single-pool, first-order, kinetic model, cellu lase (48 h) or driselase pretreatments yielded UIP predictions that we re more similar to in vivo values. Some carbohydrase and protease comb inations also yielded single time-point estimates of UIP that were sim ilar to in vivo values. Similarly, when sufficient time was permitted for protease incubation, single time-point estimates derived from prot ease alone were similar to in vivo values.