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Beware of Fescue Toxicosis in Broodmares

Livestock Update, June 1997

Larry A. Lawrence, Animal and Poultry Sciences, Virginia Tech

Tall Fescue (Festuca arundinacea) is a hardy grass that is easily established, tolerates close grazing, stands up to heavy horse traffic, and survives drought conditions that withers other grasses. Fescue is resistant to insects, disease and weed competition. It has a long growing season starting early in the spring and lasting until late in the fall and is known as the most important cool season grass in the United States.

Where can you get this "wonder grass." If you are in Virginia and have an old established pasture you probably already have it. You also probably have an endophyte infection in your stand of tall fescue. Will this endophyte infection harm your horses? It is difficult to predict, but the more you know about tall fescue the better you will be able to avoid its potential devastating effects on broodmares and newborn foals.

Fescue Related Problems Documented cases of fescue related toxicity have included some of the following common problems:

The Toxic Principle The toxic agent in fescue is associated with an endophyte fungus. The fungus lives between the plant cells and either produces a chemical or causes the fescue to produce a chemical which scientists believe to be an alkaloid toxin. Three groups of alkaloids; diaziphenanthrene, pyrrolizidine and ergot are found in endophyte infected fescue. The toxin thought to be responsible for poor performance are the ergot alkaloids produced by Acremonium coenophialun. Exactly what triggers the production of this toxin has not been determined, however, they do know that the fungus is seed borne and cannot be spread any other way. They also know that most fescue pastures are infected with the endophyte to varying degrees. Typically infections may range from 10 to 100%. Problems have been reported on farms with infections across the entire range. Cutting the grass for hay does not destroy the endophyte or reduce the alkaloid content or effect. The fungus lives within the plant and cannot be detected visually, however, you can test fescue for the level of endophyte infection.

While the mechanism that causes the reproductive problems is not absolutely known. It is thought that an alkaloid resulting from the endophyte infection causes an excess production of a neuro-active chemical, dopamine. Excess dopamine has a suppressing effect on the reproductive hormone, prolactin. Prolactin is essential to the final stages of pregnancy and birth. Without the prolactin signal, the mare's body does not realize it is time to foal.

Management Approaches There are no easy solutions to the fescue problem for broodmare owners. Current practices for dealing with the problem include the following:

  1. If you have a mare that is approaching foaling, take her off fescue pasture or hay immediately and contact your local veterinarian. Monitor udder development and the foaling process. Test to see if you have an endophyte problem.

  2. Horse producers with fescue should remove the mares from fescue fields during the last 60-90 days of pregnancy. The mares could be fed a legume hay or some other grass hay and grain on a dry lot or a paddock planted in an alternate cool season grass. This is also the time when the mare will require a slightly higher nutritional level.

  3. Eliminating the infected fescue and replanting with another grass such as bluegrass, endophyte-free fescue or orchard grass may be the best insurance. It will cost approximately $180.00 per acre to establish an orchard grass - clover pasture, no-till. The best alternative forage to plant depends on the area in which you are located, contact your county agent for more information.

  4. Many producers have tried to dilute out the effects of fescue by overseeding with clover and feeding grain. However, a study at Clemson University reported a high rate of foal deaths when mares on fescue pasture were receiving 50% of their energy from supplemental feed.

  5. The possibility that mares on fescue may not produce colostrum makes it imperative that foals are checked for failure of passive transfer (FPT). Mares only produce the antibody rich colostrum during the first 24-48 hours after foaling. Foals need to get at least 1 liter or 24 ounces of colostrum within 6-12 hours after birth. It takes 2-4 months for the foal to begin to make its own antibodies. If the mare has no milk or little milk with little or no colostrum (A clostrometer, Lane Manufacturing, Inc., Denver, Colorado can be used to test mares milk for antibodies) the foal needs to get colostrum, collected from another mare or a plasma transfusion. Time is critical. There are FPT tests that determine if adequate serum immunoglobulin (IgG) levels have been reached in foals. However, they are only accurate 18-24 hours after birth. To guard against FPT collect colostrum from mares that have normal births and adequate colostrum. Six to eight ounces of colostrum can be collected from a mare and frozen in locking plastic bags. Your veterinarian can provide more information about colostrum "banks" and plasma transfusions. When the colostrum is needed it should be defrosted slowly in a warm water bath. Do not use microwave ovens to defrost colostrum, they destroy important antibodies. These solutions increase the cost of raising horses for many producers but if endophyte infections are present they must be considered.

Medical Treatments Clinical studies of mares on endophyte infected fescue have taken several different directions. One of the most promising treatments has been successfully used experimentally by Virginia and Kentucky Veterinarians. Domperidone is a D-2 dopamine receptor antagonist that seems to relieve the prolactin-depressing effects of individual ergot alkaloids. In a controlled study one half of a group of mares grazing endophyte infected fescue were treated with Domperidone. The Domperidone treated mares had shorter gestation lengths and foaled closer to their expected foaling dates, had more mammary development, produced milk, and had higher serum prolactin and progesterone and lower serum estrogen levels. This drug is available only to veterinarians for clinical testing. For information about obtaining Domperidone contact Equi-Tox at 803/646-6443 or Dr. Dee L. Cross, Animal, Dairy and Veterinary Sciences Department PO Box 340361 Clemson University Clemson, SC 29634 - 0361. Researchers have found that it is important to match the Domperidone dose level to the alkaloid level. Auburn University will test for the alkaloid level. Samples can be sent to: Fescue Toxicity Diagnostic Center, Dept. of Botany, Plant Pathology and Microbiology, Auburn University, Alabama 36849. Actually matching dose level to alkaloid is difficult at best. The researchers suggest the most effective way to deal with the problem is dose management. If you encounter leaking of milk and the mare does not foal within 24 hours they suggest reducing the dose of Domperidone by one half.

Summary The best approach to this problem at this time is to take the mares off endophyte infected fescue pasture and hay at least 60-90 days before foaling. Keeping detailed records on each of your mares pregnancies is beneficial since mares tend to repeat the length of gestation and exhibit similar signs of parturition from year to year.

Disclaimer: Commercial products are named for informational purposes only. The author, Virginia Cooperative Extension, and Virginia Polytechnic Institute and State University do not endorse these products specifically and do not intend discrimination against other products which are not mentioned but which might also be suitable.

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