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Problems in the Horse

Management Practices

Endophyte-Free Fescue

Other Management Considerations

Ongoing Research

Tall fescue is a grass which grows on over 35 million acres of land in the United States. The USDA recently sampled pastures on horse farms throughout the US and found that 62 percent of the pastures contained endophyte fungus-infected (EI) grass. Many (57 percent) of the owners or operators of those horse farms were unaware that the EI grass was present in their pastures. As many as 700,000 horses may graze fescue pastures or be fed fescue hay each year.

What many owners may not realize is that there are some significant health risks associated with horses eating EI tall fescue. Some of these problems can be minimized with careful management of horses and pastures.

ENDOPHYTE-INFECTED FESCUE

Recognize first that it is not the fescue grass itself that is toxic to the horse, but rather an endophytic fungus known as Neotyphodium coenophialum, which lives within the plants and seeds. When the horse ingests the grass, it is steadily poisoned by alkaloids produced by the endophytic fungus. Endophyte-infected (EI) fescue grass will look perfectly healthy and nutritious to the eye. The only way you will know if your pasture grass or hay is infected is through laboratory analysis. Because of the horse’s extreme sensitivity to the toxin, fields with as little as 5-10 percent infection rates can pose potential hazards to broodmares and foals.

PROBLEMS IN THE HORSE                                                                           Back to Top

The most significant problems associated with endophyte-infected fescue relate to the horse’s reproductive performance. They include:
• Lower conception or breeding rates
• Abortions
• Prolonged pregnancy (normal gestation averages 342 days)
• Foaling difficulty (dystocia)
• Pre-mature placental separation (red-bag)
• Thick or retained placentas
• Lack of or poor milk production (agalactia)
• Low immunoglobulin (IgG) levels in milk
• Higher rates of newborn foal death
• Increased risk of laminitis
• Altered serum hormone levels

Other less significant reactions to the endophyteinfected fescue may be loose feces or diarrhea and more profuse sweating. Research in cattle has demonstrated that EI fescue also reduces growth and body condition. A similar effect has been observed in yearling horses, when they did not receive supplemental feed while grazing EI fescue.

MANAGEMENT PRACTICES                                                                          Back to Top

While research shows that some horses are able to rid their systems of the endophyte toxin and recover from its ill effects in as little as 30-45 days, a good rule-of-thumb is to remove broodmares from endophyte-infected fescue 60-90 days prior to foaling. Replace the forage with a balanced ration that includes high quality hay, grain, and supplements. If you live in an area that produces fescue hay, make sure you are not inadvertently buying hay from an endophyte-infected field. The toxin can remain in fescue hay for several years after it has been cured and baled. To dispel any doubts, choose a different variety of grass hay or feed a legume such as alfalfa. Even if a producer is advertising endophyte-free (EF) fescue hay, it would be prudent to have the hay tested before purchasing and feeding it. Contact your veterinarian about a new drug that is being developed for prevention and treatment of fescue toxicosis in pregnant mares.

ENDOPHYTE-FREE FESCUE                                                                          Back to Top

To eliminate the problems associated with endophyte-infected fescue and livestock production, researchers have developed endophyte-free (EF) and friendly-endophyte tall fescue seed. Unlike some fungi, Neotyphodium coenophialum is only spread via infected seed. If a field is established using endophyte-free seed, it should remain that way unless contaminated by seeds from infected fescue. When replanting a pasture, it is extremely important that all infected plants and seeds be destroyed prior to sowing. Seeds may remain viable in the soil for a year or more. Discuss the best methods for eliminating stands of infected fescue with an agronomist, toxicologist, or your county extension agent. It is generally recommended that an interim crop, such as an annual forage or row crop, be grown for at least one season before replanting fescue. If you choose to replant fescue, make sure the seed is certified as fungus-free. Encroachment of EI fescue back into the grass stand has been a problem in many re-seeded pastures over time.

OTHER MANAGEMENT CONSIDERATIONS                                                 Back to Top

If it is impractical to replant your endophyteinfected fescue pastures at this time, it will be especially important to heed these management practices:
• Have your pasture tested to determine the level of infection.
• Mow fields prior to the development of seed heads, which contain the highest levels of toxins in the plant.
• Remove horses from EI pastures in conditions of extreme heat or drought.
• Remove broodmares from EI pastures 30 days prior to breeding and 60-90 days prior to foaling.
• Keep accurate records of breeding and anticipated foaling dates.
• Notify your veterinarian for initiation of drug therapy if your mare has been grazing EI fescue prior to foaling.
• Monitor the mare closely during late pregnancy.
• Contact your veterinarian if impending signs of birth, including udder development, relaxation of vulva, and muscles around the tailhead fail to develop within the expected timeframe.
• Attend the birth.
• If mare fails to show signs of normal birth progression, contact your veterinarian immediately. • Keep mares and foals off EI fescue until after weaning to prevent agalactia (poor milk production).

ONGOING RESEARCH                                                                                   Back to Top

Tall fescue is the most widely grown forage grass in the country, and much of it remains infected with the Neotyphodium coenophialum fungus. While research has revealed a lot about the endophyte’s affects on horses and livestock, scientists will continue to tackle the problems associated with feeding EI fescue.

Veterinary treatments are available to offset abnormal pregnancies, difficult births, and poor milk production. Further studies will perhaps reveal other concerns relating to growth, development, body condition, and performance and what can be done to prevent them. Until then, it is important to analyze your pastures and manage your horses according to what you find.

If you have any questions or concerns, contact your veterinarian or a qualified equine nutritionist.


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