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Fescue Agalactia

By: Dr. Philip Johnson

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Fescue agalactia is primarily a problem for brood mares. This condition is the situation that occurs when brood mares ingest tall fescue at pasture (or in hay) during pregnancy. The disease is named for the fact that a critical aspect of its clinical manifestation is the failure to develop an udder and to secrete milk. The newborn foal is also effected (albeit indirectly) as a result of fescue agalactia because, without critical care, he will die due to the unavailability of milk and colostrum.

Fescue agalactia is a very common toxic disease of the pregnant mare. In most of the mid-west, south, and eastern states of the USA, tall fescue (Festuca arundinaceae) is a very hardy successful species of grass that thrives in this climate. Apart from its toxicity, tall fescue grass would be an excellent nutritional source for horses (brood mares are an exception). Remarkably, the ability of this tall fescue to succeed so extensively is attributable to the fact that it contains, within its structure, a fungus (Neotyphodium coeniophalium) known as an endophyte. The presence of this endophyte is beneficial to the well being of the fescue plant. Unfortunately, this fungus contains toxic alkaloids (such as ergovaline) that mimic the brood mare's hormones. Depending on the prevailing weather conditions, some fescue pastures are more toxic than others.

The Fescue toxins gain access to the mare's bloodstream following grazing (or ingestion of hay) and act in the brain to interfere with the production of the hormone prolactin. Prolactin is needed for both the development of the udder and for the secretion of milk. The fescue toxins also interfere with the termination of pregnancy leading to prolongation of gestation and thickening of the placental membranes.

What to Watch For

  • Failure to develop an udder
  • Failure to secrete milk and colostrum
  • Prolongation of the length of gestation
  • Increased risk for difficult foaling (dystocia)
  • Thickened placental membranes
  • Increased risk for retention of the placental membranes.

    Other Symptoms

    In those parts of the country in which Fescue toxicity is known to be common, all and any problems associated with the termination of pregnancy – the act of foaling, passage of placental membranes ("afterbirth") and lactation – are generally viewed as being likely associated with fescue until proven otherwise.

    In light of the fact that the health and well-being of the newborn foal is directly related to the availability of colostrum and milk from the mare, fescue ingestion represents the most common cause of numerous newborn foal problems in geographical areas where fescue grows. Of particular importance in this respect is foal septicemia – the situation in which the newborn foal fails to acquire any antibodies against infectious disease from the mare's udder.

    Other problems that have been attributed to fescue ingestion include increased embryonic mortality (efforts to successfully breed mares at Fescue pasture are unsuccessful), increased risk for laminitis ("founder") and increased risk for developmental orthopedic disease (in growing foals).

    Prevention

    Surprisingly few horse owners are aware of the substantial risks to both the mare and the foal when pregnant mares are allowed to graze fescue grass, so horse owner education represents a critical first step in preventing this problem. Obviously, in the ideal situation, pregnant mares should never be allowed to consume tall fescue pastures or hay. It is the last 6 to 8 weeks of gestation that represent the most critical period for avoidance of fescue. If fescue pastures cannot be avoided, they should be trimmed down to almost ground level and an alternative forage source provided (such as alfalfa or Timothy grass hay). The seed head of the tall fescue is the point of the plant at which the toxin is most concentrated. If possible, pregnant mares should be accommodated on a dry lot and fed an alternative forage source.

    Interestingly, fescue-associated toxicity problems vary significantly from year to year on a given farm, presumably due to changes in climate. Owners should not assume that fescue problems will not occur simply because they did not occur during the preceding few years. Endophyte-free strains of tall fescue can be planted but these strains tend to be quickly overgrown by endophyte-infected strains from adjacent areas. The advice of a local agronomist should be sought in respect to strategies that might help minimize endophyte-infected fescue problems.

    Mares at risk for fescue-related dystocia should be accommodated at a location where foaling can be observed and, if needed, attended. Electronic foaling alert devices (fixed to the vulva) are helpful in that they signal the onset of foaling and preclude the need for 24-hour observation. Some veterinarians advocate the measurement of calcium concentration in the udder secretions. Foaling may be anticipated as the calcium concentration increases. The newborn foal should be critically evaluated for adequacy of both antibody acquisition and sufficiency of nutrition. It is strongly recommended that the veterinarian, at some point, should examine the mare, the placental membranes (afterbirth), and the foal during the foal's first 24 hours of life.

    Treatment

    Upon recognition of fescue agalactia, affected mares should be immediately removed from fescue pastures and fed an alternative source of forage such as alfalfa or Timothy grass hay. Using ultrasound, your veterinarian should assess the health of the pregnancy and the developing fetus. Some veterinarians elect to undertake blood tests to evaluate the effect of the fescue toxins on the mare's hormones.

    In the last few years, the drug domperidone has been shown to reverse many of the effects of the fescue toxins. This drug is administered by mouth to the pregnant mare at a time close to the anticipated foaling date. Although domperidone is able to reverse the effect of fescue toxins on the udder and the termination of gestation, it likely does not undo the effects of these toxins on the thickening of the placenta. Therefore, the mare should be carefully monitored for foaling because there is still an increased risk for difficult foaling.

    Following birth of the foal, strategies used to further enhance milk secretion include: ongoing administration of domperidone for a few days; the additional injection of oxytocin; good quality food; and hot-packing of the udder. It is very important to ensure that the foal ingests sufficient colostrum – his primary source of antibody protection against bacterial pathogens during the first few weeks of life. In addition to observing the foal's interaction with the udder (ensure that the foal is ingesting the secretions and evaluate the colostrum for antibody content), a blood test at 18 to 24 hours of age is strongly recommended to ensure that sufficient antibodies gain access to the foal's circulation.

    In addition to antibodies, the milk represents the foal's primary source of nutrition. Foals born to fescue-exposed mares should be critically observed during the first few days to ensure that milk (nutritional sustenance) consumption is adequate.

    If the placental membranes have not been passed within 6 hours following birth, your veterinarian may perform specific treatments to help them pass. It is important NOT to pull retained placental membranes (afterbirth) because fatal bleeding may occur. Your veterinarian should be contacted about retained placental membranes. If the retained placental membranes are hanging to the ground, they may be collected together and tied-up in a knot to prevent the mare from standing on them and effectively pulling them out (with bleeding risk) herself.

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