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 al- falfa (2.62% N, 49.6% NDF, and in vivo undegradable intake protein (UIP) = 16.4% of CP) and prairie hay (.88% N, 69.4% NDF, and in vivo UIP = 44.5% of CP) was estimated using the Streptomyces griseus protease (SGP) in vitro method with or without pretreatment with two carbohydrases: cellulase from Penicillium funiculosum or driselase from Basidiomycetes. Drise- lase is a broad-spectrum carbohydrase. Incubating forage samples for 48 h with cellulase or driselase at a concentration of 800 mg/g per g of hay nearly maximized ADF and NDF disappearances. This con- centration and incubation time then were used to pretreat hay samples. A 2-h pretreatment was in- cluded to evaluate the potential for reducing the analysis time. Other sets of samples were or were not pretreated with acetate buffer alone. Following 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 estimated using SGP and a single-pool, first-order, kinetic model, cellulase (48 h) or driselase pretreatments yielded UIP predictions that were more similar to in vivo values. Some carbohydrase and protease combinations also yielded single time-point estimates of UIP that were similar to in vivo values. Similarly, when sufficient time was permitted for protease incubation, single time-point estimates derived from protease alone were similar to in vivo values.