PSII-7 Effect of endophyte-infected tall fescue on body weight, vital signs, and liver function of beef heifers

Abstract Tall fescue was first introduced to the United States over 70 years ago. Since then, it has become the most common forage source for beef cattle in the Southeastern region of the US. Most tall fescue establishes a symbiotic relationship with a toxic fungal endophyte (Epichloë coenophiala), which contributes to the improved vigor of the plant due to acquired resistance to grazing, insects, heat, and drought. However, when consumed by cattle, it may cause fescue toxicosis, a condition characterized by reduced feed intake, body weight (BW) loss, vasoconstriction, and impaired reproductive performance in livestock species. Therefore, the aim of this study was to investigate the effect of endophyte-infected tall fescue consumption on growth performance and health-related traits in beef cattle. For this purpose, 24 Simmental x Angus heifers were divided into two dietary treatments, in which 12 heifers received endophyte-free tall fescue seeds (E-) and 12 heifers were fed with endophyte-infected tall fescue seeds (E+, 6,764 ppb of ergovaline) mixed with the diet for 45 d. The E+ heifers received a daily dose of 20 μg of ergovaline per kg of BW. The E- heifers received the same quantity of seeds as the E+ heifers. For each heifer, phenotypes related to growth (BW), vital signs (respiration rate RR, and body temperature TEMP), and liver functions (serum albumin ALB, alkaline phosphatase ALP, aspartate aminotransferase AST, gamma-glutamyltransferase GGT, cholesterol COL, bilirubin BIL, and triglycerides TRI) were analyzed at the end of the experiment. Phenotypes were analyzed using a linear model in R with diet included as a fixed effect. For analysis of BW, the BW at the beginning of the trial was included in the model as a covariate. Results showed that COL and ALP were significantly less (P 0.05) in the E+ heifers compared with the E- (-32.92 ± 11.16 mg/dL and -32.33 ± 13.95 U/L, respectively). Conversely, E+ heifers had greater (P 0.05) BW, RR, TEMP, and AST when compared with E- heifers (-17.82 ± 5.12 kg, 25.83 ± 5.52 breaths/min, 0.56 ± 0.12 oC, and 5.83 ± 2.18 U/L, respectively). Measurements of ALB, BIL, GGT, and TRI were not different between E+ and E- heifers. Our results suggest that heifers consuming endophyte-infected tall fescue have compromised vital signs and metabolically altered liver, which may impair growth performance. This study increases our understanding of the biological mechanisms affected by the fescue toxin in beef cattle.