ALFALFA SUPPLEMENTATION OF CORNCOB DIETS FOR SHEEP: EFFECT OF RUMINAL OR POSTRUMINAL SUPPLY OF PROTEIN ON INTAKE, DIGESTIBILITY, DIGESTA, PASSAGE AND LIVEWEIGHT CHANGES
In trial 1, nine wethers (18 mo old; 50 kg liveweight) fitted with tubes inserted into the abomasum, were assigned to three 3 × 3 Latin squares to determine effects of supplementing a basal diet of ground corncobs with either alfalfa (30% of dry matter intake) or soy protein (60 g d−1 infused postruminally). In each period, following determination of effect of supplementation on intake, digestibility and digesta passage were determined, the latter by pulse dosing with chromium mordanted cell walls from cobs through the feed. Total dry matter intakes were increased (P < 0.05) from 780 g d−1 to 1143 g d−1 by the supplements with a corresponding improvement in liveweight gain, but there was no difference between supplements. Apparent digestibilities of dry matter, organic matter and cell wall were decreased (P < 0.05) by alfalfa supplementation but not by soy protein infusion; however, intakes of digestible energy were identical for both supplements. Relative to the basal diet, alfalfa increased digesta passage but not rumen fill whereas infusion of soy protein increased digesta fill in the rumen but not digesta passage. In trial 2, addition of soy protein directly to the basal diet resulted in an intake similar to alfalfa supplementation (1154 vs. 1262 g dry matter d−1 respectively). Fecal output, estimated using a single compartment model to describe digesta passage through the tract, yielded results similar to those obtained by total collection. Key words: Roughage (poor quality), abomasal infusion, chromium-mordanted cell walls, fecal output estimation