Ergovaline

Ergovaline is an ergot alkaloid produced by the endophyte Neotyphodium coenophialum found in tall fescue[1]. It is known to be unstable and affected by many variables, including the type of extraction solvent, amount of light and heat exposure, and the amount of time the ergot alkaloid has been dissolved[1]. Ergovaline and its stereoisomer, ergovalinine, are often present in solution, and the degree of epimerization from ergovaline to ergovalinine depends on these variables[1].

Ergovaline is a major endophyte-derived ergopeptine alkaloid in infected tall fescue and is the causative agent of fescue toxicosis or “fescue foot”[3]. It is a vasoconstrictor known to compromise circulation to the hooves and has been shown to have pronounced effects on blood pressure and heart rate in mice, with high concentrations causing vasoconstriction and bradycardia[3]. Ergovaline has also been found to bind to D2 dopamine receptors and elicit second messenger responses similar to that of dopamine[4].

In the context of horse pasture management, researchers at the University of Kentucky measure endophyte and ergovaline, as well as pasture species composition, to calculate ergovaline in broodmare pastures[5]. While no exact threshold of ergovaline in the total diet has been established for broodmares, the University of Kentucky uses 200 ppb as an accepted threshold value because mares demonstrated constriction of the distal palmar artery at this level[5]. The risk for late-term pregnant mares grazing pastures in the 201-500 ppb range is moderate, but this risk can be diminished by reducing ergovaline in the diet through pasture management[5]. Pastures over 500 ppb are considered unsafe for late-term pregnant mares[5].

New cultivars of tall fescue that contain a novel endophyte have been developed, which produce alkaloids that imbue the plant with desirable plant characteristics, such as drought tolerance and insect resistance, but do not produce the alkaloids that are harmful to late-pregnant mares[5].

Citations:

[1] https://www.frontiersin.org/articles/10.3389/fchem.2014.00076/full

[2] https://www.mdpi.com/2072-6651/13/10/683

[3] https://www.nature.com/articles/s41598-020-66358-2

[4] https://pubmed.ncbi.nlm.nih.gov/7665369/

[5] https://ker.com/equinews/fescue-toxicosis-in-mares-how-much-ergovaline-is-too-much/