166 Effects of dietary inclusion of Silvafeed plant extract supplements on performance and health of heifers grazing endophyte-infected tall fescue

Supplemental plant extracts may improve animal health status and performance of cattle grazing endophyte-infected (E+) toxic tall fescue. The objective was to assess dietary inclusion of Silvafeed plant extracts on heifer performance and physiological measures associated with fescue toxicosis and vaccine response. A total of 44 yearling heifers (292.6 ± 29.0 kg) were maintained as a single group on E+ tall fescue prior to the start of the treatment period. Heifers were assigned to one of three treatment groups: 1) E+ pastures with soybean hulls (SH; n = 3 pastures), 2) E+ pastures with soybean hulls and BX additive (BX; 10 g/heifer daily; n = 3 pastures), and 3) E+ pastures with soybean hulls and ATX additive (ATX; 5 g/heifer daily; n = 3 pastures). Treatments were administered over an 84-d period between April and June and offered as-fed at 1.8 kg/heifer daily. Heifer body weight and hair coat scores were recorded on d 0, 28, 56, and 84 relative to the start of the treatment period. On d 56, heifers received a modified live multivalent BRD vaccine and serum samples were collected on d 0, 14, and 28 relative to vaccination. Samples for blood urea nitrogen (BUN) collected on d 56 were analyzed by colorimetric methods. Serum prolactin collected on d 84 was analyzed by radioimmunoassay. Heifer body weight, average daily gain (ADG), hair coat scores, and BHV-1 titers were analyzed using the LME4 package of R. Pairwise comparisons were conducted using the EMMEANS package of R. Data from d 0 was used as a covariate with pasture block included as a random effect. Serum prolactin and BUN were analyzed using the MIXED procedure of SAS with treatment as a fixed effect and block as a random effect. Heifer body weight (P ≥ 0.1), hair coat scores (P ≥ 0.1), and ADG (P = 0.40) did not differ between treatments over the 84-d treatment period. However, there was a tendency for an increase in ADG of heifers receiving ATX (0.53 kg/d) and BX (0.49 kg/d) relative to heifers receiving SH only (0.23 kg/d) between d 56 and d 84 (P = 0.07). There was no impact of treatment on BHV-1 titers (P ≥ 0.1). Serum prolactin (P = 0.97) and BUN (P = 0.38) did not differ between treatments. Preliminary results show the potential for improved weight gain, suggesting further investigation with more experimental units is warranted.