Diagnosis > Equine

Fescue is a pasture plant, which is normally quite hardy. The plant may become infected by endophytes which can then produce ergot alkaloids (ergopeptine alkaloids). Horses lack pre-gastric metabolism of alkaloids unlike ruminants and hence horses could be at a greater risk to larger doses of alkaloids when consuming endophyte-infected pasture. Horses suffering from endophyte fescue toxicity may have a poor appetite, lose weight/condition, reduced performance, have a rough coat and develop an elevated temperature.

Endophytes may also have negative effects on the reproductive system of mares, as mares are sensitive to alkaloid concentrations as low as 300-500ppb. Common symptoms of ergot alkaloid poisoning in pregnant mares are:

• Extended gestation to 12 months
• Dystocia
• Red bag delivery
• Thick oedematous placentas
• Weak/dead foals with aspiration pneumonia
• Difficulty in foals breaking through toughened placenta
• Lack of mammary development or lactation
• Stillbirths

Heavily pregnant mares should be removed from fescue pasture contaminated with endophytes by 300 days of gestation. Two weeks prior to the expected delivery date, mares can be treated with domperidone to reduce the effects of ergot alkaloid toxicity. Lactating mares exposed to endophyte-infected tall fescue can have reduced concentrations of IgG in milk. This in turn can predispose foals to septicaemia which may result in death.

Laboratory tests for ergovaline (the ergot alkaloid of fescue toxicity) and lolitrem B (the ergot alkaloid of perennial rye grass) are commonly available for veterinary investigation. Ergot alkaloids cause vasoconstriction which can predispose equine digits to laminitis. Ergot alkaloids cause post-capillary vasoconstriction, increased capillary hydrostatic pressure, and transvascular fluid movement, resulting in increased tissue pressure, oedema, vascular collapse and ischemia (Cross, 1997).

Neotyphodium coenophialum is an endophyte which causes fescue toxicity by producing ergot alkaloids and it spends its whole life cycle within the plant. N.coenophalium causes dystocia in mares and deaths of perinatal foals.

Ryegrass tremorgens causes ryegrass staggers in horses. This endophyte proliferates in hot dry conditions followed by periods of rain. Symptoms of ryegrass staggers include ataxia, head shaking, loss of co-ordination and eventual collapse.  Horses that may be standing quietly, when “spooked” can completely over-react. Fortunately the neurological effects appear temporary and when horses are removed from the pasture the horse usually returns to normal after a week or so.

These endophytes may be passed from one generation of plants to the next via the seeds. It is important to make sure that purchased seed is endophyte-free prior to seeding pastures for horses.

Intervention level
The maximum tolerable level of ergovaline in horses is thought to be 0.3-0.5ppm. It is difficult to analyse for other ergopeptine alkaloids, as there is a lack of control standards.