Effects of Injectable Trace Minerals at the Start of the Breeding Season on Attainment of Pregnancy in Commercial Beef Cows

Abstract Text: Our objective was to evaluate the effects of a single application of injectable trace minerals (ITM; MultiMin 90, MultiMin USA, Inc., Fort Collins, CO) on pregnancy attainment of lactating beef cows. Mature Brahman x British crossbred beef cows (n = 3,750) were enrolled from 14 separate commercial cow/calf operations in central and southern Florida. Ranch breeding season ranged from 90 to 120 d with study enrollment < 30 d after the start of the breeding season. During enrollment, cows were administered 5 mL of ITM or sterile saline subcutaneously in alternating order. The ITM contained 60, 10, 15, and 5 mg/mL of Zn, Mn, Cu, and Se, respectively. At the time of treatment administration, cow body condition score (BCS) was recorded and assigned a BCS category group (1 = low; 2 = moderate; 3 = high). In addition, samples of pasture forage and trace mineral supplement were collected. To estimate ranch trace mineral status, liver biopsy samples were collected from 10% (maximum of 16) of the enrolled cows. Treatment assignment was identified by an individual number and color coded ear tag. Tags were removed during pregnancy diagnosis. Overall tag loss was low and equally distributed between treatments (96.3 and 95.5% tag recovery for ITM and Saline, respectively) resulting in a total of 3,597 collected tags for pregnancy analysis. Average Se and Cu were highly variable among ranches (Se, range = 0.39 – 4.36 and average = 1.14 ± 1.04 mg/kg DM; Cu, range = 65 – 307 and average = 158 ± 78 mg/kg DM). There were 5 and 3 ranches classified as Se and Cu deficient (liver concentrations < 0.60 and 100 mg/kg DM, respectively). There was no ranch x treatment interaction (P = 0.50) or overall treatment effect (P = 0.19) for pregnancy attainment (88.8 and 87.2% pregnant for ITM and Saline, respectively; SEM = 0.88). Attainment of pregnancy increased (P < 0.001) with increasing BCS category (83.9, 86.7, and 91.0 for low, medium and high BCS categories, respectively). Interestingly, although not statistically significant (P = 0.62), the numeric difference between the percentage pregnancy attainment due to ITM increased as cow BCS decreased (3.1, 1.8, and 0.1% for low, medium, and high BCS categories, respectively). Provided at the start of the breeding season, ITM injection did not significantly improve pregnancy outcome in the commercial cow/calf ranches enrolled in this study.

Keywords: injectable trace minerals, cow, pregnancy