THE NUTRITIVE VALUE OF PRESSURE-STEAMED ASPEN (POPULUS TREMULOIDES) FOR MATURE SHEEP
Four rumen-fistulated sheep, 62 kg average body weight (BW), were assigned four pelleted diets containing 0 (control), 15, 30 and 45% steam-processed aspen (SPA) in a 4 × 4 Latin square design. All diets were formulated to be isonitrogenous to the control diet which contained 45% ground alfalfa hay as a roughage source. Intake of dry matter (DM), crude protein (CP), crude fiber (CF) and gross energy (GE) per kg BW0.75 were not affected (P > 0.05) by addition of SPA to pelleted sheep diets. However, digestible energy (DE) consumption apparently decreased with SPA diets. Apparent digestibilities of DM and GE significantly (P < 0.05) decreased for the SPA diets; however, CP and CF digestibility coefficients and N retention were not different (P > 0.05) among the four treatments. Ruminal pH for all treatments fell rapidly within 1 h post feeding and remained low to 12 h, whereas ammonia (NH3) levels were significantly (P < 0.05) elevated for all aspen-fed animals, from 1 h through 12 h post feeding. Total VFA concentrations and molar concentrations of acetic, propionic and butyric acids in ruminal fluid were comparatively lower for sheep fed the 45% SPA diet versus those receiving the other treatments. Blood serum glucose concentration was significantly (P < 0.05) depressed when 45% SPA was fed to mature sheep.