Effects of supplementing a Bacillus-based direct-fed microbial on performance and immune function of beef heifers grazing endophyte-infected tall fescue pastures

Objective

Our objective was to evaluate the effects of a Bacillus-based direct-fed microbial (DFM) on performance and immune function of beef heifers grazing endophyte-infected tall fescue pastures.

Materials and Methods

Crossbred beef heifers (n = 192; 196 kg ± 15.4 kg) were randomly assigned to 24 pastures (1.8 ha; 8 heifers/pasture; 12 pastures/treatment). Each day heifers received 2.83 kg (as-fed basis) of a commodity mix containing equal parts cracked corn, soyhull pellets, dried distillers grains. Treatments were created with a vitamin and mineral supplement containing a Bacillus-based DFM (BOVA; 3 g/head per day) or without additional additives (control) included in the commodity mix (50 kg of mineral/1,000 kg of commodity mix). Heifers were weighed every 28 d. Two heifers per pasture were randomly selected a priori for blood draws at each weighing to measure plasma cytokine concentration. The same heifers also received ova egg albumin injections on d 1 and 14, with additional blood collected on d 14, 28, 42, and 56 for serum albumin IgG measurement.

Results and Discussion

Body weight and ADG were not different between treatments. Feeding BOVA reduced the proinflammatory cytokines IL-1α and IFN-γ, along with the anti-inflammatory cytokine IL-1 F5 and the chemokines MIG and MIP-1 β. However, TNF-α, IFN-αA, IL-21, IL-13, and IP-10 were not affected by treatment. Egg albumin IgG did not differ between treatments.

Implications and Applications

The reduction of cytokines indicates that supplementing a Bacillus-based DFM may reduce inflammation in beef heifers grazing endophyte-infected tall fescue.