THE GRASS ISN'T ALWAYS GREENER; Symptoms and Treatments of Fescue Toxicosis
by Dr. Dee L. Cross
If you are a breeder, you better take a second look at the mares grazing in your pastures. An endophytic fungus, Acremonium coenophialum, in tall fescue has been reported to cause reproductive problems in pregnant mares. A study at Clemson University examined the effects of fescue toxins on pregnant mares. The results were unequivocal. Mares grazed on fescue infected with endophyte showed the following symptoms of fescue toxicosis:
Even when infected fescue diets were supplemented with selenium or phenothiazine, fescue toxicosis symptoms still prevailed. In an effort to reduce the intake of toxins, mares on infected pastures were supplemented with enough grain to supply 50% of their National Research Council (NRC) requirements for energy.
Unfortunately, the grain supplementation on EI pasture was of no benefit. Clemson researchers lost half of the mares and two-thirds of the foals to fescue toxicosis in this study. These results exposed the impact of endophyte fescue on horses, especially to a breeding facility with many pastured broodmares.
Endophyte is prevalent in fescue-growing regions throughout the United States. Fescue toxicosis, however, appears to have regional and seasonal preferences. Veterinarians in the more northern regions of the US report lower toxicity levels, agalatia and dystocia, while premature placental separations (red bagging) appear more frequently. On the other hand, a warm or mild winter in Northern states tends to exacerbate toxicosis conditions. In the more Southern fescue-growing regions in the US, count on a high level of fescue toxicosis in mares regardless of the severity of winter weather.
WHAT CAN YOU DO?
What can you do to prevent fescue toxicosis in your herd? There are many options. Dr. John Mayo of Mayo and Rofe Equine Clinic in Middlesburg, Va, suggests the following steps for breeding managers in VA: Have broodmare pastures evaluated for toxin levels, especially if fescue is suspected or is prevalent in the area. Send a sample to the local extension agent to have the forage tested. Evaluate past records and the history of the farm. If problems such as low milk levels or weak foals increase after mild winters, or if toxicosis suymptoms decrease after a hard winter, then endophyte is probably present. Observe for fescue toxicosis symptoms as indicated in Dr. Cross' study. Any of these symptoms in breeding mares could indicate an endophyte problem.
If endophyte is suspected in a broodmare pasture, remove pregnant mares 60 to 90 days before foaling. Thirty days is an absolute minimum. If removing mares from the pasture is not an option, studies showed that domperidone, available from your veterinarian, is the most effective means of relieving fescue toxicosis symptoms.
Studies show that domperidone-treated mares have shorter gestation lengths, have live foals that are born closer to their expected delivery dates, have more mammary development, are not agalactic and have higher prolactin and progesterone levels.
The daily oral domperidone paste, which was developed at Clemson, is started 20 days prior to the expected foaling date if mares remain on toxic fescue up to parturition. If mares are removed from fescue, then starting the paste 10 to 14 days prior to the expected delivery date, depending on the condition of the mare, is recommended. However, mares that appear to be progressing normally after removal from toxic pasture may need little or no drug treatment.
If a mare foals and is agalactic, the pharmaceutical can be used daily for five days after foaling to bring the mare into milk production. Researchers at Clemson have used domperidone for up to ten days on mares left on toxic fescue after foaling.
"The drug obviously helps," Dr. Mayo observes. "Some mares with little or no milk will be put on domperidone and will increase milk letdown in as little as one day. We've been very pleased with it."
Horsemen should consult with a veterinarian when fescue toxicosis is present or when using domperidone to evaluate reproductive problems in mares and prevention of the disease. Furthermore, Mayo suggests that domperidone is favorable over thyroid medicine in treating fescue toxicosis symptoms. Domperidone, he states, helps reverse the trend better and gets mares "turned around."
Are there any other options? Initially, extension service personnel in the fescue growing regions of the US recommended replacing infected fescue with endophyte-free varieties of tall fescue. They suggested destroying the infected pasture with a herbicide such as Roundup™ and replanting the pasture with newly developed endophyte-free varieties of fescue. This method, however, has not proven to be very effective or efficient for the following reasons; it requires a large investment in time and resources. After two to three years there is a high probability of reappearance of significant levels of infected fescue in these pastures. Since horses are very sensitive to the toxins of fescue, even the smallest levels of endophyte can produce equine fescue toxicosis. Even when EF varieties of tall fescue are planted in pastures where endophyte varieties were never present, maintenance of a pure stand of non-infected fescue may be difficult, especially in the southern regions of the fescue-growing areas of the US. The method requires movement of animals to other fields for a season and is one of the most expensive approaches to preventing fescue toxicosis. Most horsemen know these limitations are not feasible.
Any other options? Michael Hughes, manager of Rockburn Farms in Marshall, VA, has a first-hand account of treating infected fescue. About five years ago, the farm decided to destroy the broodmare's pastures with Roundup™ and replant the fields with orchard grass, bluegrass, rye, and red clover. Though the practice will probably have to be implemented again in about two or three years, Hughes claims it was a success.
"If you have the space to switch the mares to other pastures for a season and if you can afford it, I recommend this method. However, I don't suggest using EF varieties," Hughes comments.
If removing fescue is the method of choice on the farm, don't reseed with endophyte-free varieties. Best results have been obtained by using chemicals like Gramaxone™ or Roundup™ spray in combination with "choke crops" for a period of at least two years. These crops grow a very dense canopy, thus "choking out" competitive grasses like infected fescue. Contact your local extension agent for successful choke crops in the area."
According to Dr. Mayo, however, there is no panacea.
"Managers must integrate many sound management practices into the breeding program to alleviate fescue toxicosis symptoms," Dr. Mayo suggests. "In VA, severity varies from season to season and from mare to mare, making the problem difficult to treat. Managers should work closely with their veterinarian and keep accurate records to evaluate different methods for controlling reproductive problems caused by fescue toxicosis."
Dr. Dee L. Cross is a professor of animal sciences at Clemson University. He is currently researching nutritional toxicology, working with many different species, but specializing in cattle and horses. Dr. Cross received an undergraduate degree from Austin Peay University in Clarksville, TN, and MS and PhD in animal nutrition from the University of KY. As the author of over 200 scientific publications, Dr. Cross is the holder of 2 patents. Dr. Cross is currently the department head at Clemson University.
Dr. John Mayo is the senior member of the largest private equine practice in VA, Mayo and Rofe Equine Clinic, Inc. He received his DVM degree from the University of GA and is a former president of the VA Veterinary Medical Association. Dr. Mayo holds many delegate positions in various veterinary associations, including the AAEP, AVMA, FEI, AHSA and USCTA.
Gretchen Fathauer's comments:
This sounds very promising. Still, it does not explain why some horses on my farm never had a problem grazing in my large fields that are primarily fescue, regardless of the season or year. I also wonder why my horse can thrive on hay made in this same field, without foundering, while if he eats the same grass fresh and green, he founders. He can be out in the big field of fescue during winter with no ill effects, however. My hay customers have been feeding my predominantly fescue hay to pregnant mares with no problems--normal pregnancies and large, healthy foals.
.....So many unanswered questions! But restoring optimum circulation through a free boarding situation--constant turnout in a herd--with maintaining a correct hoof shape through frequent correct trims to enable hoof mechanism, is a step in the right direction.
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