In situ evaluation of ruminal degradability and intestinal digestibility of extruded soybeans

Abstract

Two ruminally cannulated Jersey cows were used to determine in situ ruminal degradability and intestinal digestibility of raw (E0) soybeans and soybeans extruded at 145°C (E145), 155°C (E155) and 165°C (E165). The degradation of dry matter (DM) and crude protein (CP) was estimated using nylon bags suspended in rumen for 2, 4, 8, 12, 16, 24 and 48 h calculating the effective ruminal degradabilities (ERD) for an assumed outflow rate of 0.06/h. Four extra sample bags were incubated for 12 h to determine CP digestibility using the mobile nylon bag method. Cows were fed a ration of 30% concentrate and 70% meadow hay. Soybean extrusion at all temperatures decreased the effective protein degradability significantly (P < 0.05). Soybean processing at the highest heat input (E165) decreased ERD (44.0%) in the rumen significantly while the values for E145 and E155 were similar, 50.8 and 50.3% respectively. Soybean extrusion at all tested temperatures was followed by a significant (P < 0.05) reduction in the proportion of the rapidly degraded DM and CP fractions a, and both the increased proportions and reduced breakdown rate (c) of the fraction b. The intestinal protein digestibility values of the rumen-undegraded protein of extruded soybean were somewhat higher, however the observed differences between treatments were not significant (P < 0.05). Estimated intestinal digestibilities were 87.2, 89.7, 92.0 and 92.6% for E0, E145, E155 and E165, respectively.