- Definition
- Pathophysiology
- Systems Affected
- Genetics
- Incidence/Prevalence
- Geographic Distribution
- Signalment
- Signs
- Causes
- Risk Factors
BASICS
- Toxicosis in pregnant mares associated with ingestion of endophyte-infected tall fescue (Festuca arundinacea Schreb.) during late gestation (i.e. post gestation day 300)
- The endophyte is a fungus (Neotyphodium coenophialum) that lives in a mutualistic relationship within the intercellular spaces of the plant. Previous names for the fungus include Acremonium coenophialum and Epichloë typhina
- The endophyte produces ergot peptide alkaloids, the most prominent being ergovaline
- The ergot peptide alkaloids produced by the endophyte are mycotoxins—secondary metabolites of a fungus
- Ergot peptides act as dopamine agonists, binding D2-dopamine receptors and suppressing prolactin secretion
- Prolactin affects not only mammary development and milk production but also lipogenesis, immunity, and reproductive hormones
- Tall fescue occupies >35 million acres in the USA and is especially prominent in the southeast
- Most tall fescue pastures derive from a Kentucky 31 variety released in 1943 that was contaminated by an endophyte; >95% of tall fescue pastures are estimated to contain this endophyte
- An estimated 688 000 horses are maintained on tall fescue pastures
- 1 survey indicated that 53% of pregnant mares maintained on fescue pastures were agalactic, 38% had prolonged gestation, and 18% had stillborn or weak foals that died
Tall fescue is most prominent in the southeastern USA, but it can be found over much of the eastern USA and is grown for grass seed in the Pacific Northwest.
Pregnant mares during late gestation, with the last 30 days of pregnancy (i.e. post gestation day 300) being the most critical.
- Lack of udder development in mare
- Mare is past her due date
- “Red bag presentation” with premature placental separation of chorioallantois preceding foal through birth canal
- Mare is having foaling problem
- Weak foal with “dummy-like” behavior
- Lower average daily gain is possible in yearlings not supplemented with concentrates
- Typically, mares are 3–4 weeks past their due date
- Agalactia in mares; milk appears brown or straw-colored rather than white
- Larger-than-normal foal or inadequate preparation of the reproductive tract may cause dystocia; foal may be turned 90° in the pelvis
- Placenta may be thickened enough that the foal has trouble breaking through, and the mare may retain the placenta
- Foals are weak or stillborn
- Foals are large and gangly, with long and fine hair coats, poor muscle mass, overgrown hooves, and nonerupted incisor teeth (i.e. dysmature)
- Foals may be hypothyroid, with signs of incoordination and poor suckling reflex
- Foals may suffer from failure of passive transfer of colostral antibodies due to mare agalactia; septicemia in foals is common
- Any tall fescue should be considered infected by the endophyte unless the owner has purposely planted an endophyte-free variety
- Lower percentages of fescue in mixed pastures decrease the severity or likelihood of problems; however, minimal toxic concentrations of ergovaline in endophyte-infected tall fescue have not been determined for horses; any tall fescue exposure should be considered potentially toxic for mares
- Ergovaline concentrations are highest in seed heads during summer months; concentrations are increased by drought, excessive rain, and fertilization
- Fescue hay retains its toxicity
- Non-endophyte-infected fescue cannot become infected; however, endophyte-infected fescue will outcompete non-endophyte-infected fescue and will eventually take over a pasture
DIAGNOSIS
TREATMENT
MEDICATIONS
FOLLOW-UP
MISCELLANEOUS