Soybean meal mitigates vasoconstriction and serotonin suppression during fescue toxicosis in beef cattle

Authors: SOUSA, LUIZ - University Of Kentucky; Davis, Brittany; HARMON, DAVID - University Of Kentucky; TROTTA, RONALD - University Of Kentucky

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/21/2026
Publication Date: 4/10/2026
Citation: Sousa, L.C., Davis, B.E., Harmon, D.L., Trotta, R.J. 2026. Soybean meal mitigates vasoconstriction and serotonin suppression during fescue toxicosis in beef cattle. Journal of Animal Science. 104. Article skag108. https://doi.org/10.1093/jas/skag108.
DOI: https://doi.org/10.1093/jas/skag108

Interpretive Summary: Fescue toxicosis, caused by the consumption of ergot alkaloids from toxic endophyte-infected tall fescue grass (TE) decreases the growth of over 9 million calves in the Southeastern U.S. annually. Our objectives were to evaluate the effects of soybean hulls, whole soybean, and soybean meal supplementation on the mitigation of ergot alkaloid-induced vasoconstriction, heat stress susceptibility, and systemic immunity in beef cattle during fescue toxicosis. Feed intake, meal duration, and meal size were not affected by treatments. Steers receiving TE increased the number of meals compared with steers fed non-toxic endophyte-infected tall fescue seed (NTE) and TE + soybean meal. Soybean meal supplementation mitigated fescue toxicosis vasoconstriction and promoted peripheral blood flow, as evidenced by a 10.4% increase in caudal artery cross-sectional area relative to the pre-treatment baseline, and decreased systolic blood pressure compared with TE steers. Measures of heat stress (respiration rate, and rectal temperature) were not influenced by soybean feed supplementation. Soybean meal supplementation increased serum serotonin by up to 34% compared with other TE-containing treatments. Among the soybean-based feeds evaluated, soybean meal was the most effective because of the observed vasodilatory benefits and the restoration of serum serotonin and normal feeding behavior in beef cattle challenged with fescue toxicosis.

Technical Abstract: The objectives were to evaluate the effects of soybean hulls, whole soybeans, or soybean meal supplementation on the mitigation of vasoconstrictive, heat stress, and inflammatory responses in beef cattle during fescue toxicosis. Ten ruminally-cannulated Angus ' Holstein steers were used in a 5 ' 10 Latin rectangle design. Five treatments were evaluated: 1) non-toxic endophyte-infected tall fescue seed (NTE), 2) toxic endophyte-infected tall fescue seed (TE), 3) TE + soybean hulls (SBH), 4) TE + whole soybean (WSB), or 5) TE + soybean meal (SBM). Treatment periods lasted 7 d, followed by a 14-d washout. Feed intake and feeding behavior were recorded daily. Caudal artery hemodynamics were assessed before feeding (0 h), 4 h, and 8 h after the morning feeding on days -1 (baseline) and 7. Physiological stress measures (skin and rectal temperatures, respiration rate, blood pressure, heart rate) were collected at 0 h, 4 h, and 8 h on days 1 and 7. Blood samples were collected at 0 h and 4-h on days 1 and 7. Treatments did not influence (P = 0.35) total dry matter (DM) intake, basal diet DM intake, meal duration, or meal size. Steers receiving TE or TE + WSB consumed a greater (P = 0.02) number of meals compared with NTE and TE + SBH steers. Relative caudal artery cross-sectional area decreased (P = 0.02) by 8.62% for steers receiving TE and increased (P = 0.02) by 10.4% for steers receiving TE + SBM. Systolic blood pressure of the caudal artery tended to increase (P = 0.06) in steers fed TE compared with steers receiving NTE or TE + SBM. Respiration rate, rectal temperature, and neck skin temperature were not influenced by soybean feed supplementation (P = 0.24). Rump skin temperature decreased (P = 0.02) in steers receiving TE compared with NTE and TE + SBM. Soybean meal supplementation increased (P = 0.01) serum serotonin concentration by up to 34% compared with other TE-containing treatments. Dietary supplementation of soybean-based feeds has the potential to alleviate symptoms of fescue toxicosis in cattle. Among soybean-based feeds evaluated, soybean meal was the most effective because of the mitigation of ergot alkaloid-induced vasoconstriction, promotion of vasodilation, and restoration of serum serotonin and normal feeding behavior in beef cattle challenged with fescue toxicosis.