Ergot is a fungus Claviceps purpurae that grows on rye and other grasses and grains such as wheat, oats, ryegrass, and sorghum. The toxins produced by Claviceps are ergotamine and ergonovine. Weeds contaminated with the fungus may infest other grain and seed crops and contaminate hay. Another endophyte fungus infesting tall fescue grass also produces a toxic ergot alkaloid ergovaline.
The mycotoxin alkaloids produced by the Claviceps ergot cause spasm of the peripheral blood vessels (vasoconstriction) reducing blood flow to the extremities and if prolonged produce a dry gangrene of the feet, tail end and ear tips. Central nervous system stimulation can also be a feature with excitability. Ergotamine acts on the uterine muscle rather like the hormone oxytocin causing uterine contractions and occasional abortion, but also inhibits the hormone prolactin which is responsible for the development of the mammary gland during pregnancy, thereby suppressing milk production.
Ergovaline from the endophyte fungus of tall fescue has similar effects inhibiting lactation and causing imbalances in the hormones oestrogen and progesterone leading to prolonged pregnancy in mares. The placenta may become thickened and result in so called ‘’Red bag’’ delivery at birth with weak foals which have poorly developed lung function and fail to thrive.
Prevention. Mares should be removed from fescue pasture at least one month before foaling. Endophyte free strains of Fescue are now available and should be sown in preference to the old varieties. Any affected animals should be removed from their pasture and the ration changed. Exposed mares from tall fescue pastures may reportedly respond to domperidone 1.1mg/kg orally for 10-14 days (Dalefield. Veterinary Toxicology for Australia & New Zealand 2017 pp380-382)