Effects of Dietary Inclusion of Tannin-Based Supplements on Performance and Health of Yearling Beef Heifers Grazing Toxic, Endophyte-Infected Tall Fescue

This study evaluated dietary inclusion of tannin-based feed additives on heifer performance and physiological measures associated with fescue toxicosis and vaccine response. Forty-five yearling beef heifers (292.6 ± 29.0 kg) grazing toxic, endophyte-infected (E+) tall fescue pastures were assigned to 1 of 3 treatment groups: (1) soybean hulls (SH; <i>n</i> = 3 pastures), (2) SH and BX tannin-saponin additive (BX; 10.0 g heifer^-1 d^-1; <i>n</i> = 3 pastures), and (3) SH and ATX tannin-polyphenol additive (ATX; 5.0 g heifer^-1 d^-1; <i>n</i> = 3 pastures). Treatments were administered over an 84 d period. Data were analyzed using R and SAS 9.4 with treatment as a fixed effect, block as a random effect, and pasture as the experimental unit. Treatment effects were assessed at the pasture level. Average daily gain (ADG) of heifers receiving ATX (0.53 kg/d) and BX (0.49 kg/d) were increased relative to heifers receiving SH only (0.23 kg/d) between D56 and D84 (<i>p</i> = 0.07). There was no impact of treatment on other performance measures (<i>p</i> > 0.15) or on serum metabolite responses including bovine herpesvirus type 1 (BHV-1) titers (<i>p</i> > 0.15), prolactin (<i>p</i> = 0.97), haptoglobin (<i>p</i> = 0.26), and blood urea nitrogen (BUN; <i>p</i> = 0.38). Preliminary results show the potential for improved weight gain, suggesting further investigation with more experimental units is warranted.