Date of Graduation

8-2018

Document Type

Thesis

Degree Name

Master of Science in Animal Science (MS)

Degree Level

Graduate

Department

Animal Science

Advisor/Mentor

Kegley, Elizabeth B.

Committee Member

Beck, Paul A.

Second Committee Member

Powell, Jeremy G.

Third Committee Member

Zhao, Jiangchao

Keywords

Beef Cattle; Health; Yeast

Abstract

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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