Effects of isoflavone supplementation, via red clover hay, on the growth and postgraze physiological recovery of beef steers grazing endophyte-infected tall fescue pastures

Authors: Davis, Brittany; JACOBS, ALAYNA - Oak Ridge Institute For Science And Education (ORISE); Flythe, Michael; Hamilton, Tracy; JI, HUIHUA - University Of Kentucky; SCHRICK, NEAL - University Of Tennessee; GOODMAN, JACK - University Of Kentucky

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/11/2025
Publication Date: 9/5/2025
Citation: Davis, B.E., Jacobs, A.A., Flythe, M.D., Hamilton, T.A., Ji, H., Schrick, N.F., Goodman, J.P. 2025. Effects of isoflavone supplementation, via red clover hay, on the growth and postgraze physiological recovery of beef steers grazing endophyte-infected tall fescue pastures. Journal of Animal Science. 103. Article skaf304. https://doi.org/10.1093/jas/skaf304.
DOI: https://doi.org/10.1093/jas/skaf304

Interpretive Summary: Endophyte-infected (E+) tall fescue is an important forage for livestock operations, but cattle consuming this forage can develop fescue toxicosis with symptoms including depressed prolactin levels, vasoconstriction, and decreased growth rates that can persist as long as five weeks after grazing. Isoflavones found naturally in forage legumes, such as red clover, can alleviate fescue toxicosis symptoms. This study was conducted to determine if isoflavone supplementation via red clover hay, daily or every other day, would improve growth performance of beef steers while grazing E+ tall fescue pastures and reduce postgraze recovery time. Steers supplemented with isoflavones via red clover hay daily or every other day had greater weight gain over the grazing period and had shorter postgraze recovery from prolactin depression and vasoconstriction, when compared with steers supplemented with a common isoflavone-free protein supplement, dried distillers’ grains with solubles. The results of this study suggest that isoflavone supplementation could be an effective management strategy to alleviate fescue toxicosis related health and performance losses in beef steers, both during and after grazing. More research is needed to determine how isoflavone supplementation while grazing E+ tall fescue could benefit the health and performance of cattle when transitioning to the finishing phase of production.

Technical Abstract: Livestock grazing endophyte-infected (E+) tall fescue can exhibit persistent systemic vasoconstriction and fescue toxicosis. Isoflavones in legumes, most notably red clover (RC), are known hypotensive agents. The objective of the experiment was to evaluate the effect of isoflavone supplementation via RC hay, every day or every other day (QOD), on average daily gain (ADG) of steers grazing E+ tall fescue pastures and their physiological recovery after grazing when managed on a non-toxic diet (28-d). In Spring 2018 (62-d) and 2019 (65-d), 36 Angus × steers were blocked by initial body weight (BW) into pastures (n = 6 pastures year-1) assigned to one of three supplement treatments: Dried distillers’ grain with solubles (DDGS) only (CON; pasture + DDGS), 7.5% RC hay daily (7.5%-RC; pasture + DDGS + RC hay), or 7.5% RC hay every other day (7.5%-RC QOD; daily rotation of either: CON or 7.5%-RC). All supplements were isonitrogenous, and shrunk BW was collected at the start and end of the grazing period for determination of ADG. Each year, immediately after the grazing period, three steers were randomly selected from each pasture and moved to outdoor partially covered pens where they were fed a non-toxic diet for a recovery period of 28-d. The caudal artery of each steer was imaged immediately after grazing and then every 7-d over the recovery period using Doppler ultrasonography to monitor artery luminal areas (CAA). Jugular blood samples were collected immediately after grazing and on d-28 of recovery for determination of serum prolactin. Data were analyzed using the Mixed procedure of SAS with repeated measures and significance was set at P = 0.05. Steer ADG was greater with 7.5%-RC daily or QOD (7.5%-RC: 0.77 kg d-1; 7.5%-RC QOD: 0.83 kg d-1), compared to CON (0.55 kg d-1; P < 0.01). Isoflavone supplementation via RC hay during the grazing period resulted in 2.5× larger CAA and higher serum prolactin concentrations at the end of grazing and over the recovery period, respectfully, compared with CON steers (P < 0.05). Furthermore, steers supplemented with 7.5%-RC during the grazing period were never vasoconstricted over the recovery period, but CON steers did not exhibit CAA recovery until d-21 (P < 0.05). Supplementation of isoflavones via RC hay daily or QOD, is an effective management strategy to improve ADG in cattle grazing E+ tall fescue pastures and reducing the time required for physiological recovery post-grazing.