Date of Graduation


Document Type


Degree Name

Master of Science in Animal Science (MS)

Degree Level



Animal Science


Elizabeth Kegley

Committee Member

Paul Beck

Second Committee Member

Jeremy Powell

Third Committee Member

Jiangchao Zhao


Beef Cattle, Health, Yeast


Supplemental dietary yeast products are beneficial during times of stress. Calves experience increased levels of stress during birth, weaning, and the post-weaning receiving period. Therefore, 3 experiments were conducted to determine how yeast supplementation affects growth performance and health during this time. In experiment 1, 2 truckloads of highly stressed calves (n = 175; initial body weight [BW] = 226 ± 24.5 kg) were assigned randomly to 1 of 3 treatments; unsupplemented control, or supplementation with 2 commercial yeast products (Y1 and Y2). Average daily gain (ADG) was not different (P = 0.99) during the 28 d receiving period; nor was there any difference (P = 0.29) in the percentage of calves treated for bovine respiratory disease. In experiment 2, heifer calves (n = 95; initial BW = 165 ± 27 kg) were randomly assigned to pastures and pastures were randomly assigned to treatment: 1) no yeast (CON), or 2) addition of yeast product (YP). Heifers were supplied treatments for 35 d prior to weaning and through a 42-d backgrounding period. Average daily gain prior to weaning was not different (P ≥ 0.45) between treatments. However, CON had increased (P = 0.01) ADG compared to YP from weaning to the end of the backgrounding period. Microbiome analysis found that supplemental yeast did not dramatically change α or β diversity nor was there a difference in community structure for rumen bacteria; fecal α or β diversity were different on d 34. In experiment 3, late gestation cows (n = 97) were supplemented YP approximately 45 d prior to parturition. At parturition colostrum and blood samples (n = 30) were collected to determine the effect on passive transfer. Supplementation ended 22 d after the last calf was born (d 85). Body weight on d 85 was greater (P = 0.01) for YP calves compared with CON. Cows that were supplemented YP had a lower (P = 0.03) neutrophil:lymphocyte at hour 0 and 48 after parturition. Similarly, calves on YP treatment had a lower (P = 0.02) neutrophil:lymphocyte at hour 48. Overall, effects of yeast supplementation have been variable between the 3 experiments.

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