The objective of this study was to determine the effects of supplemental Bacillus subtilis (BS, 0.5 × 1011 CFU/day), injectable vitamin E and selenium (ES, 1000 mg α-tocopherol acetate and 10 mg sodium selenite), or both during the transition period on health parameters and the incidence of retained fetal membranes (RFM) of dairy cows under tropical conditions (average temperature humidity index = 77.0). Thirty-two crossbred Holstein-Friesian cows were used in a randomized design trial with a 2 × 2 factorial arrangement of treatments. Cows were randomly assigned to one of four treatments, including no supplementation (CON), single intramuscular injection of ES on day - 21 before the expected calving date (ES), daily oral supplementation of BS between day - 21 and day 21 relative to calving, or both ES and BS. Body condition score (BCS) and blood samples were collected on days - 28, - 14, 0, 14, and 28 relative to calving. Mean concentrations of corpuscular hemoglobin were higher (33.12 vs 34.03 g/dL, p = 0.06) and platelets were lower (380.97 vs 302.32 × 103/μL, p = 0.10) with ES than without ES. Cows fed supplemental BS had lower concentrations of creatinine and albumin and tended to have lower AST and β-hydroxybutyrate (BHBA) levels. However, concentrations of glucose were higher for cows fed BS than for those without BS. No differences in the incidence of RFM were observed. In summary, supplemental B. subtilis could reduce indicators of negative energy balance by increasing glucose and lowering BHBA and improve health parameters by keeping WBCs and monocytes in a healthy range during the transition period.
Keywords: B. subtilis; Health parameters; Selenium; Transition period; Tropical environment; Vitamin E.