Huber, German Miguel2019-08-202019-08-202019-05https://hdl.handle.net/11299/206170University of Minnesota M.S. thesis. May 2019. Major: Animal Sciences. Advisor: Alfredo DiCostanzo. 1 computer file (PDF); vi, 90 pages.Two experiments were conducted to determine the interaction of dietary roughage and sulfur concentration on performance of beef cattle, and effects of two dietary concentrations of Levucell SC in growing or finishing feedlot diets. In the first experiment, effect of various dietary concentrations of roughage (R) and sulfur (S) on performance of beef cattle fed finishing diets were examined. Eighty-four steers (initial BW 461 ± 36 kg), were allocated to one of four treatments in a randomized complete block design. Block was constituted by breed and source: 18 Angus-crossbred (Block 1), 30 Angus-Limousin (Block 2), or 36 Charolais steers (Block 3). Steers were fed in a Calan gate individual feeding system and treatments were arranged in a 2 x 3 factorial, with two dietary concentrations of S (0.28%, LS or 0.56%, HS) and three dietary concentrations of R (5%, LR; 10%, MR; 15%, HR). Steers were harvested after 134 d (blocks 1 and 2) and 92 d (block 3) on feed. Final carcass-adjusted BW was not affected by R, S, or their interaction (P ≥ 0.44), and averaged 641 kg across treatments. Dry matter intake increased linearly (P = 0.01) with increasing R. Greater dietary S concentration decreased (P = 0.02) DMI. Average daily gain was not affected (P ≥ 0.24) by R, S, or their interaction, and averaged 1.48 kg across treatments. Feed efficiency was not affected by dietary S concentration or the interaction (P ≥ 0.96), but decreased linearly (P = 0.01) with increasing R. Hot carcass weight (413 kg across treatments), LM area (100.2 sq. cm), 12th rib fat thickness (1.17 cm), marbling score (459), and frequency of individual USDA quality grades were not affected by S, R, or their interaction (P ≥ 0.14). A tendency (P = 0.03) for fewer carcasses grading USDA yield grade 1 and 2 was observed with increasing R. Results suggest that increasing dietary R concentration increases DMI and decreases feed efficiency while high dietary S concentrations decrease DMI. However, no interactions occurred to suggest that performance may be enhanced by feeding increased R in high-S feedlot diets. In the second experiment, effect of Saccharomyces cerevisiae (SC; Levucell SC 20) on growing and finishing steers were examined. Forty-seven Angus and Simmental steers were allocated in a randomized complete block design during a growing (Exp. 1; Initial BW = 341 ± 6.8 kg) and finishing (Exp. 2; Initial BW = 430 ± 7.7 kg) experiment to one of three dietary treatments: 0, 500, or 1,000 mg of SC/hd daily (SC0, SC500, and SC1000, respectively). Basal diets for Exp. 1 (1.14 Mcal NEg/kg, 15.6% CP) and Exp. 2 (1.39 Mcal NEg/kg, 16.7% CP) consisted primarily of corn earlage and modified distillers grains (MDG; Exp. 1) or dry-rolled corn and MDG (Exp. 2). Steers were fed in a Calan-gate individual feeding system and were weighed every 28 d throughout each experiment. Experiment 1 and Exp. 2 lasted 56 d and 115 d, respectively. For Exp.1, final BW (432 kg) and ADG (1.61 kg) were not affected (P ≥ 0.36) by treatment. In Exp. 1, DMI averaged 9.02, 9.02, and 9.84 kg/d (linear P = 0.12), and G:F averaged 0.178, 0.182, and 0.166 (linear P = 0.12, quadratic P = 0.17) for SC0, SC500, and SC1000, respectively. At the end of the step-up feeding period in Exp. 2 (0 to 28 d), ADG averaged 1.63, 1.97, and 1.88 kg (linear P = 0.16, quadratic P = 0.15) and G:F averaged 0.158, 0.189, and 0.183 (linear P = 0.11, quadratic P = 0.19) for SC0, SC500, and SC1000, respectively. In Exp. 2, DMI averaged 12.05, 11.34, and 11.09 kg/d (linear P = 0.13) for SC0, SC500, and SC1000, respectively. In Exp. 2, ADG averaged 1.77 kg and G:F averaged 0.156 and neither was affected (P ≥ 0.30) by SC inclusion. Inclusion of SC did not affect (P ≥ 0.16) HCW, 12th rib fat thickness, ribeye area, marbling score, or frequency of individual USDA quality or yield grades. Results suggest that using dietary SC concentration may increase DMI in high-forage growing diets. The linear trend for reduced DMI in finishing cattle fed live yeast merits further research to determine effects on feed efficiency. Keywords: Yeast, Cattle, Saccharomyces cerevisiae, Roughage, Distillers GrainsenThesis or Dissertation