Effect of the addition of live yeast (Saccharomyces cerevisiae) on growth and carcass quality of steers fed high-forage or high-grain diets and on feed digestibility and in situ degradability

The effects of adding yeast culture (Saccharomyces cerevisiae, 5 x [10.sup.9] live organisms/g of growth medium) at 10 g/steer daily to three diets consisting of 75% alfalfa silage and 25% barley, 96% corn silage and 4.0% soybean meal, or 75% dry-rolled barley and 25% alfalfa hay on performance of growing and finishing steers and carcass characteristics, feed digestibility, and degradability in the rumen were determined. In separate trials over 2 yr, the performance of steers fed the three diets with no supplementary live yeast (control; C) or with live yeast (Y) was determined using 72 Hereford steer calves in eight pens each year in a randomized complete block design. The diets were fed sequentially and the steers were randomized before diets were switched. Each year at the end of the high-grain feeding segment of the trial, the steers were slaughtered when ultrasound backfat was such that the carcass would grade A1 or A2 (Canadian grades). The digestibility of feed DM, CP, and NDF of the three diets was determined sequentially using six and eight mature, ruminally cannulated steers in 2 yr, respectively. The degradation characteristics of the three diets in the rumen were determined using the nylon bag technique in two steers for each additive treatment. In the 1st yr, the feed efficiency of the corn silage diet was lower (P < .05) for C than for Y steers (5.9 vs 6.8). Differences (P < .05) were not observed between C and Y steers for any of the performance or carcass characteristics. The rate of degradation of alfalfa silage diet DM was decreased (P < .05) in the 1st yr for the steers receiving Y (15.8 vs 12.2 %/h, C vs Y). Addition of live yeast did not result in significant positive effects on feed utilization.