Date of Graduation

5-2026

Document Type

Thesis

Degree Name

Bachelor of Science in Agricultural, Food and Life Sciences

Degree Level

Undergraduate

Department

Animal Science

Advisor/Mentor

Dr. Elizabeth Kegley

Committee Member

Dr. Jeremy Powell

Second Committee Member

Dr. Ken Coffey

Abstract

Due to the increased risk of bacterial populations developing resistance to current antibiotics, consumer perceptions surrounding the utilization of antibiotics use in cattle, and the endemic incidence of bovine respiratory disease (BRD) among growing and finishing cattle, alternative management strategies to improve the health of cattle must be developed. The objective of this study was to evaluate the use of a supplement containing a yeast culture and an essential oils blend (YEO) on the health and growth performance of stocker calves at high-risk for BRD. Crossbred male beef calves (n = 185) received on two separate dates were used in a 42-d study. Upon arrival (d -1), calves were weighed, ear tagged, ear notched for persistent-infected bovine viral diarrhea virus testing and were housed in a common pen overnight with ad libitum access to bermudagrass hay and water. The next day (d 0), cattle were stratified by body weight and arrival castration status (steer or bull) and assigned to 1 of 8 pens (10 to 12 calves/pen). Cattle were vaccinated for clostridial and respiratory pathogens, treated with an anthelmintic, branded, and castrated (if necessary) on d 0. Within each truckload, pens were assigned randomly to 1 of 2 dietary treatments which were: 1) a corn-distillers’ grain-soybean meal-based supplement with no YEO (CON), and 2) the CON supplement with the addition of YEO with a target intake of 2.5 g/calf daily. Supplements were formulated for offering at 0.9, 1.4, and 1.8 kg/day and increased as consumption rose. Body weights were taken initially (d -1 and 0) and prior to supplement feeding on days 14, 28, 41, and 42. Cattle were observed daily for signs of clinical BRD. If presenting symptoms of BRD and if rectal temperature was ≥ 40°C, cattle were deemed morbid and treated with an antibiotic according to a standard preplanned protocol. Data were analyzed using MIXED and GLIMMIX procedures of SAS 9.4. Truckload was a random effect and pen within truckload was specified as the subject. Significance was declared if P ≤ 0.05 and tendencies were declared if 0.05 < P ≤ 0.10. Supplementing YEO for the duration of the 42-d trial did not affect body weights (P ≥ 0.7974; CON = 273 kg, YEO = 274 kg) or average daily gain (P ≥ 0.2069; CON = 0.81 kg/d, YEO = 0.81 kg/d). Morbidity rates (P ≥ 0.1752; CON = 45%, YEO = 46%), day of antibiotic administration (P ≥ 0.2186), or rectal temperatures (P ≥ 0.1718) associated with BRD were not improved by YEO supplementation. To conclude, the inclusion of this YEO did not improve overall growth performance or incidence of BRD in high-risk beef calves within this 42-d receiving period; however, continued investigation is needed for future product formulations.

Keywords

Receiving Cattle; DFM; BRD; Yeast; Essential Oil

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