Date of Graduation

5-2026

Document Type

Thesis

Degree Name

Bachelor of Science in Biology

Degree Level

Undergraduate

Department

Biological Sciences

Advisor/Mentor

Jeremy Powell

Committee Member

Jeremy Beaulieu

Second Committee Member

Jeffery Lewis

Third Committee Member

Faith Lessner

Abstract

The objective was to assess the effect of a probiotic microbial gel (BIOFRESH® Microbial Gel, Agrarian Solutions) administered on arrival in combination with feeding one of two different direct-fed microbials (DFM 365a or DFM 365b, Agrarian Solutions) on the health and growth performance of stocker calves at high risk for bovine respiratory disease (BRD). Beef heifer calves (n = 292, BW = 476 ± 5 lb) arriving on 3 separate receiving dates were used in the 42-day receiving study. On arrival (d -1), heifers were processed, stratified by d -1 body weight, and then assigned randomly to 9 pens (10 to 12 heifers/pen; total of 27 pens). Within truckloads, pens were assigned randomly to dietary treatment (9 pens/treatment). Calves were housed on 0.45 ha grass paddocks and fed grain supplements that served as carriers of the direct-fed microbial dietary treatments. The treatments were: 1) CON (grain supplement with no direct fed microbial), 2) DFMaGEL (dose of probiotic gel on d 0 then subsequent feeding of grain supplement with DFM 365a, intake goal 1.25g/heifer each day), and 3) DFMbGEL (dose of probiotic gel on d 0 then subsequent feeding of grain supplement with DFM 365b, intake goal 2.50g/heifer each day). Weights were recorded initially (d -1 and 0) and before feeding on days 14, 28, 41, and 42. Cattle were observed daily for morbidity, and cattle that presented symptoms of BRD and had rectal temperature ≥ 40°C were treated with antibiotics using a standard predetermined protocol. Statistical analyses were performed using MIXED and GLIMMIX procedures of SAS 9.4 with truckload as a random effect and pen within truckload specified as the subject. Supplementing cattle for the first 42 days after arrival with DFMaGel and DFMbGEL treatments did not result in differences in body weights (P ≥ 0.65) or average daily gain (P ≥ 0.46) when compared to calves receiving the CON. There was a numerical advantage in overall gain for the calves receiving the DFMbGEL treatment (P = 0.46; CON = 0.88, DFMaGEL = 0.84, DFMbGEL = 0.92 kg/d). Treatments did not affect morbidity incidences within this receiving period (P ≥ 0.12; CON= 48%, DFMaGEL= 44%, DFMbGEL= 55%, SEM= 8%). The antibiotic-associated costs (P = 0.36; CON = $14.03, DFMaGEL = $14.31, DFMbGEL = $18.43) did not differ between treatments. In conclusion, administering a probiotic gel at processing in combination with either direct-fed microbial supplement did not affect the overall health or growth performance during this 42-d receiving period in high-risk beef heifer calves.

Keywords

Bovine Respiratory Disease; Direct-Fed Microbials; Probiotic Microbial Gel; Stocker Cattle; Growth Performance; Cattle Health

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