You & Your Pet by Dr. Wise

Rhode Island Veterinary Medical Association 11 South Angell Street #347 · Providence, RI 02906 (877) 521-0103 (866) 277-0238 Toll-Free ·Fax

Our neighbors lost their newborn foal and their veterinarian said it was due to fescue fungus.  Now we are concerned about whether our broodmares are safe on the pasture. 

Tall fescue is the most widely grown forage grass in the United States.  Experience on farms and in research studies indicate that this grass may either cause devastating foal losses or provide safe, inexpensive nutrition for horses.   Horse breeders need to understand why this is true.  The culprit is not the grass itself, but a fungus that specifically infects fescue.  The fungus in question is an "endophyte" which means that it grows inside the plants and can be detected only by laboratory testing.  It does not adversely affect plant growth.   The fungus is transmitted only through the seed.  It is not harbored in the soil and does not spread from plant to plant.  Whether or not a particular plant is infected depends solely on whether the seed from which it grew was infected with live fungus.  Reproductive difficulties in mares grazing on fescue have been widely recognized and documented.  Specific problems identified are:

• Difficulty in anticipating birth - There may be little normal visual signs of impending birth such as udder development or vulvar swelling.
• Prolonged gestation - Mares may go more than 365 days (average gestation is 336 days).
• Dystocia - difficult foalings and large foals
• Placenta problems - abnormally thick and/or tough placentas; placentas which detach prematurely from the uterus causing weak or even dead foals; retained placentas that can lead to laminitis, septicemia and reduced ability for the mare to reproduce in the future.
• Agalactia - mares produce little or no milk resulting in weak foals and questionable transfer of colostral antibodies to foals.
• Foal death - due to difficult deliveries, early placental detachment or lack of colostral milk.

An experimental drug, domperidone, has been used to treat mares that have been on fescue.  It has given excellent results in agalactic mares and stimulated milk production within 24-48 hours after administration.   However, because of all the problems associated with the fungus, it is best not to graze broodmares on fescue during the later part of their pregnancy.  Studies indicate that avoiding fescue 30-45 days prior to foaling will greatly reduce the likelihood of reproduction and lactation problems. 

This information, prepared as a public service by the Rhode Island Veterinary Medical Association, answers problems Rhode Island veterinarians currently are seeing in their practices, as well as new developments in animal care.