Effects of overseeding red clover in endophyte-infected tall fescue pastures on steer physiology and performance

Authors: Harlow, Brittany; Flythe, Michael; Hamilton, Tracy; JI, HUIHUA - University Of Kentucky; SCHRICK, F. NEAL - University Of Kentucky; AIKEN, GLEN - University Of Florida

Submitted to: Applied Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2021
Publication Date: 11/23/2021
Citation: Harlow, B.E., Flythe, M.D., Hamilton, T.A., Ji, H., Schrick, F., Aiken, G.E. 2021. Effects of overseeding red clover in endophyte-infected tall fescue pastures on steer physiology and performance. Applied Animal Science. 37(6):748-757. https://doi.org/10.15232/aas.2021-02152.
DOI: https://doi.org/10.15232/aas.2021-02152

Interpretive Summary: all fescue is the most prevalent cool-season perennial grass in the United States. The vast majority of tall fescue is infected by a fungal endophyte that produces alkaloids allowing the perennial grass to be persistent and productive over a wide range of environments. Unfortunately, the fungus also produces ergot alkaloids that can cause a toxicosis that annually costs the U.S. beef industry ~$1 billion in lost production. Cattle suffering from fescue toxicosis often have poor performance and health due to vasoconstriction caused by consumption of ergot alkaloids. Therefore, strategies to mitigate fescue toxicosis are of great interest. Interseeding toxic endophyte-infected tall fescue pastures with red clover has long been recommended to mitigate performance losses and the negative health impacts of fescue toxicosis. Historically, the benefits of interseeded clover have been attributed to dilution of ergot alkaloids in the diet and improved overall diet quality. More recently, our research group has identified another mechanism by which clovers can mitigate fescue toxicosis. Clovers and other legumes produce phytoestrogenic isoflavones that when consumed cause vasodilation and increased blood flow, mitigating the vasoconstriction associated with fescue toxicosis. Given that isoflavones ameliorate ergot alkaloid-induced vasocontriction, management approaches to supplement isoflavones to grazing livestock could be a viable strategy to mitigate the impacts of fescue toxicosis. Therefore, the objective of the current study was to evaluate the impact of interseeding red clover on cattle grazing endophyte-infected tall fescue pastures. Over two spring grazing seasons, Angus cross steers were assigned to endophyte-infected tall fescue pastures with or without interseeded red clover. Following the grazing trial each year, steers were placed in pens for 1-week to monitor vasoconstriction in the caudal artery using Doppler Ultrasonography. Steers grazing pastures with interseeded red clover had greater average daily gains and exhibited increased vasodilation post-grazing. The impact of this research is that interseeding red clover in endophyte-infected tall fescue pastures can ameliorate the adverse effects of fescue toxicosis. Notably, this is the first study that has demonstrated that interseeding red clover is an effective pasture management strategy to elicit the vasoactive benefits of isoflavones.

Technical Abstract: The objective was to determine the impact of interseeding red clover on cattle grazing endophyte-infected tall fescue pastures. The hypothesis was that cattle grazing interseeded red clover pastures would have greater performance and decreased physiological impacts of fescue toxicosis from consumed ergot alkaloids (increased prolactin and vasodilation). A grazing study was conducted over 2 early growing seasons (2016 and 2017) with 24 cross bred steers each year. Prior to the start of the study in 2016, four, 3-ha pastures of mixed, cool-season grass (predominately toxic endophyte-infected, tall fescue) were blocked and randomly assigned to a control treatment (TF CON) or to an interseeded red clover treatment (TF + RC; Kenland variety, frost-seeded Feb. 2015 and 2016, 9 kg seed ha-1). Steers were blocked by BW and assigned to each pasture (n = 6 tester steers/pasture). Pastures were divided into two 1.5-ha paddocks to allow for 14-d rotational stocking, and stocking rates were varied using put-and-take steers. Pastures were grazed from 11 May to 25 July 2016 and 20 April to 20 June 2017 to provide 75- and 61-d of grazing, respectively. Serum prolactin was assayed on the last day of grazing and selected tester steers from each pasture (n = 3) were moved to pens for Doppler ultrasound measurements (caudal artery luminal area), 7-d post-grazing. Data were analyzed by repeated measures using the mixed procedure of SAS. Red clover was successfully established in TF + RC pastures at 36% and 57% of the pasture ground cover in 2016 and 2017, respectively. In result, TF + RC pastures had lower ADF and NDF concentrations resulting in greater IVTD than observed in TF CON pastures post-grazing (P < 0.05, in all cases). However, there was no effect of interseeding red clover on forage mass or pasture carrying capacity (P > 0.05). Steers grazing TF + RC pastures had 53% and 58% greater ADG and BW gain per hectare than TF CON steers, respectively (P < 0.05, in both cases). Serum prolactin concentrations at the termination of grazing were 90% greater in TF + RC steers than in TF CON (P < 0.05). Additionally, 7-d post grazing, TF + RC steers had 44% larger caudal artery luminal areas than TF CON steers (P < 0.05). The results of this study demonstrate that interseeding red clover in endophyte-infected tall fescue pastures can ameliorate the adverse effects of fescue toxicosis and is the first study to demonstrate the vasoactive impacts of isoflavones in grazing cattle.