Fescue Toxicosis

Your grass could endanger your mare's pregnancy and your horse-breeding program.

Tall fescue is the most common perennial grass pasture found in most parts of the eastern half of the United States. It was brought to North America in the late 1800s from Europe and became popular with the release of the “Kentucky 31” strain in 1943 because it is easily established, toler¬ates close grazing, stands up to heavy horse traffic,

survives drought conditions and is resistant to weeds. Today, it covers more than 35 million acres. Unfortunately, it is not without problems. In the mid-1970s, U.S. Department of Agriculture scientists discovered an endophytic fungus (Acremonium coenophialum) that infects fescue grass. The endophyte is associated with problems in many grazing animals, but the most pronounced problems are seen in pregnant mares. Pregnant mares grazing endophyte-infected fescue pastures or fed endophyte-infected fescue hay often abort during late pregnancy, have difficulty foaling or deliver stillborn foals. Because the endophyte suppresses progesterone production, infected mares may carry their foals for 30 to 40 days longer than normal, resulting in a difficult birth and foal death.

Whether you’re an experienced breeder or looking to get into horse breeding, it’s important to know the facts. AQHA’s Horse Reproduction report will teach you everything from good breeding conformation to reproduction problems and their solutions.

Thickened placentas, premature separation of the placenta (“red-bagging”) and/or retained placentas are also common and can result in excessive uterine bleeding, uterine infections and a delay in rebreeding. If these are not problems enough, mares on fescue may have reduced milk production or no milk at all. Colostrum production may be decreased or nonexistent as well. Horse owners who think they have fescue grass need to assess their situations carefully. The first step is to verify for certain that your pasture is indeed infected and at what level. Your local county Cooperative Extension office is the best source of information on plant identification and diagnostic sampling. Once the level of endophyte infection is known, there are several options to deal with the problem.

  1. If feasible, pregnant mares should be removed from endophyte-infected tall fescue pastures or fescue hay 45 to 90 days before foaling. Removal might be to a dry lot area where non-fescue hay and grain is fed or to a pasture consisting of forage other than endophyte-infected tall fescue.
  2. The drug domperidone stimulates normal prolactin and progesterone production and has been shown to mediate the effects of fescue toxicosis and, therefore, stimulates milk/colostrum production, as well as normal placental formation. Mares on domperidone have shorter gestation lengths, live foals that are born closer to their normal delivery date and produce adequate amounts of milk. It should be administered daily for the 30 days prior to foaling.
  3. The greatest concentration of endophyte is in the mature seed head, so clipping the pasture will reduce the amount of endophyte but not completely eliminate it.
  4. The endophyte or its products (alkaloids) can be diluted through the use of other forages in the diet. Growing legumes with infected fescue is a good option. You not only get the desired dilution effect but you also receive an added benefit of improved pasture production and quality.
  5. Some specialists recommend replacing infected fescue pastures with endophyte-free varieties of tall fescue. Due to cost, this might not be an option. However, endophyte-free seed varieties are readily available. The old infected stand and all shattered seed (that might give rise to infected volunteer plants) must be eliminated and the endophyte-free variety planted.

Breeding horses involves more than selecting a mare and stallion. There are costs involved, caring for the mare during pregnancy and possible reproductive problems that could arise. Learn the facts from AQHA’s Horse Reproduction report.

There are no easy solutions to the fescue problem for mare owners. However, research continues on the effects of fescue toxicity on horses and better seed varieties, as well as treatment options that might become available in the future. In the interim, evaluate your individual operation and choose the management options that best fits your needs and abilities.