Evaluation of the stress‐reducing effect of trace mineral injection in beef calves

BACKGROUND: Little is known about the effects of trace mineral supplementation on the stress response in beef calves. OBJECTIVES: To investigate the effect of injectable trace mineral supplementation (ITM) on the stress response in beef calves exposed to different types of stress. ANIMALS: Thirty weaned Angus and Angus crossbred calves. METHODS: The enrolled calves were randomly assigned to 2 groups: ITM, 15 calves received modified‐live virus vaccine (MLV) and ITM SC and 15 calves received MLV and saline SC (CONT). The calves were exposed to 3 types of stress: the stress of MLV vaccination (d0), nasal aerosol with bovine viral diarrhea virus‐2 (BVDV‐2) challenge (d5), and liver biopsy (d26). The calves' body weights and health status were monitored. Leukocyte counts, serum cortisol concentration ([cort]), BVDV‐2 serum neutralizing antibodies (SNA), and percentages of CD4(+), CD8(+), WC1(+) (,) and CD25(+) T‐lymphocytes were measured. RESULTS: Serum cortisol concentration ([cort]) showed strong associations with the percentage of CD8(+) (r ( s ) = .50), BVDV2‐SNA (r ( s ) = −.43), and WC1CD25(+) (r ( s ) = .41) cells, and rectal temperature (r ( s ) = .40). The highest [cort] was reported 3 days after aerosol BVDV‐2 challenge. Serum [cort] was decreased in ITM‐treated calves 3 days post‐BVDV‐2 challenge, compared with CONT calves, with an average decrease of 18.5 ng/μL (95% confidence interval [CI], −6.07 to −31.3). The ITM‐treated calves were heavier and healthier (P < .01) than the CONT calves. CONCLUSIONS AND CLINICAL IMPORTANCE: Trace mineral supplementation appears to have stress mitigation effects in beef cattle that may reflect positively on growth and health performance. Viral exposure is associated with a high degree of stress, which is considered a major welfare concern.