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Fescue Toxicosis and Broodmares

Fescue Toxicosis and Broodmares








Fescue Toxicosis and Broodmares









Tall Fescue (Festuca arundinacea) is a hardy grass that is known as the most important cool season grass in the United States.  It is easily established, tolerates close grazing, stands up to heavy horse traffic, is resistant to insects, disease and weed competition and survives drought conditions that withers other grasses. It also has a long growing season starting early in the spring and lasting until late in the fall. Tall fescue is adapted to a wide range of soils, but does best on clay soils high in organic matter. Tall fescue is well adapted to the "transition zone" of the United States where summers are too hot and humid for cool season grasses and winters too cold for warm season grasses. In the South, tall fescue is best adapted to those states in the transition zone - Oklahoma, Arkansas, Missouri, Tennessee, Kentucky, Virginia and northern parts of North Carolina, Georgia and Texas.

Tall fescue does produce short rhizomes but has a bunch-type growth habit - it spreads primarily by erect tillers. Individual tillers, or stems, terminate in an inflorescence, reach 3 to 4 feet in height, and have broad, dark green basal leaves. Leaf blades are glossy on the underside and serrated on the margins. The leaf sheath is smooth and the ligule is a short membrane. The inflorescence is a compact panicle, 3 to 4 inches long with lanceolate spikelets one-half inch or more long. The grass flowers in the spring and seed mature in early summer. Seed are 4 to 7 mm long, elliptic and awned.  Tall fescue requires frequent watering during summer months, which does help to discourage fescue in the southern region.

If you think this is something you would love to have in your pastures, and you have an established pasture in one of the "green" areas on the map, you probably already have it.   While there are several varieties, if in the cool part of the year, you see beautiful deep green grass growing in clumps, that is fescue.  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.

There are newer varieties of fescue that is endophyte free and make good horse pastures.  To find out if your fescue is free of endophyte's, see your county agent for instructions for collecting and testing the fescue on your property.

Some of the commonm documented problems with Fescue toxicity are the following:

1) Abortions may occur around the time the mare would be expected to foal. Mares may carry foals for 27 to 40 days longer than normal. During the prolonged gestation the foals continue to grow and the birth is often difficult because of the size of the foal.

2) Thickened placentas are often seen in mares grazing fescue. Mares may retain the placenta longer than normal leading to infection, laminitis (founder) and difficult rebreeding.  The placenta is thick, heavy and deep red.  You also may be presented with an angry red sac at birth.  Retained placentas happened in 50% of the cases.

3) The most common problem of mares on fescue is that they produce little or no milk (agalactia) and the production of colostrum can be decreased.  Your foal may be nursing but not receiving an adequate supply of colostrum.  Checking IGg levels on all foals whose dam may have eaten fescue is strongly advised.

4) The mare may not exhibit the typical signs of foaling.

5) The number of stillborn foals doubled.

6) Prolactin and progesterone is decreased.

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, your county agent 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.  However, the last stages of pregnancy is not the only time ill effects are caused by ingestion. (see the article below: The Effects of Endophyte-Ridden Fescue on Early Pregnancy)

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

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.

Horse producers with fescue should remove the mares from fescue fields during the last 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.  Be aware that this action alone is no guarantee that you will avoid fescue related problems.

Eliminating the infected fescue and replanting with another grass such as bluegrass, endophyte-free fescue or orchard grass has often been recommended.. 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, Virginia, 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 the 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 Virginia, 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."

Many producers have tried to dilute out the effects of fescue by overseeding with clover and feeding grain. However, in a study at Clemson University researchers lost half of the mares and two-thirds of the foals to fescue toxicosis,  although mares on fescue pasture were receiving 50% of their energy from supplemental feed.

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 of the US, count on a high level of fescue toxicosis in mares regardless of the severity of winter weather.

What can YOU do?

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.

The daily oral domperidone paste 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".

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.


It has been well known that fescue grass containing the endophytic fungus, Acremonium coenophialum, has detrimental effects on pregnant mares when consumed during late gestation. Common problems include prolonged gestation, dystocia (foaling problems), agalactia (no milk production) thickened placenta, poor foal viability and decreased concentrations of prolactin and progesterone. However, few studies have evaluated the effects of this fungus on early pregnancy. Dr. J.P. Brendemuehl, at Tuskegee University in Alabama, has done some work with respect to the effects of infected fescue on the transitional mare.

During spring transition, the number and size of follicles from January through April were found to be lower and smaller in mares grazing on endophyte-infected fescue pastures compared to mares on non-endophyte pastures. The time to first ovulation was also delayed 43 days in mares ingesting infected fescue (May 28 vs. April 15). Brendemuehl and coworkers also found that cycling mares were affected by endophyte-ridden fescue. Prolonged luteal function, decreased pregnancy rates on a per cycle basis and increased embryonic death rates were all evident in cycling mares that grazed on infected fescue. Forty-five percent (45 %) of the mares on infected pastures were pregnant 14 days after ovulation compared to 75 % of mares that grazed on endophyte-free fescue.

Also noted 30 % of those mares ingesting the endophyte-ridden fescue lost their pregnancies during early embryonic development compared to 10 % of the mares on endophyte-free pastures. From these data, it appears evident that endophyte-ridden fescue can have dramatic effects on the transitional and cycling mare.

The objective of a recent study by Arns and coworkers (1997) was to investigate the effects of increasing dietary concentrations of ergovaline, the problematic ergot alkaloid produced by A. coenophialum, on establishment and maintenance of pregnancy in the mare. Earlier work by Brendemuehl, (1994) examined the reproductive status of bred mares ingesting 1171 Ng ergovaline/g wet grass.

Therefore, Arns and associates felt it necessary to evaluate the effects of lower levels of ergovaline consumption. Twelve cycling mares of light-horse breeds were randomly assigned to receive diets that contained either no ergovaline, low levels (150158 ppb ergovaline/kg total diet) of ergovaline or high levels (308315 ppb ergovaline/kg total diet) of ergovaline. The diet of each mare consisted of 52 % orchard grass and 48 % grain concentrate. Dietary ergovaline was introduced as infected fescue seed mixed into the concentrate.

Following 7 days of diet acclimation, reproductive cycles of all mares were monitored for follicular development and ovulation. Mares in estrus were bred every other day by artificial insemination once a follicle reached 30 mm in size. In evaluating body condition score, those mares fed the high ergovaline (HE) diet tended to have a lower average daily weight gain compared to those mares fed no ergovaline (NE). Mares on low ergovaline (LE) diets had no difference in average daily gain. Reproductive efficiency was measured by overall conception rates, cycles per conception, length of estrus and preovulatory size of follicles. All of these parameters were found to be similar for mares in all three groups. Consumption of infected fescue seed also did not have an effect on embryonic vesicular sizes on day 14, 21 or 28 of gestation. There were however, higher progesterone concentrations during the luteal phase in mares fed LE or HE diets. Also, prolactin concentrations were lower in LE and HE mares.

The researchers of this study believe that weight loss occurred as a result of a decrease in food consumption rather than a direct effect from injecting ergot alkaloids. Also, small sample size and individual variation may have been responsible for the lower progesterone concentrations found in mares fed no ergovaline. Brendemuchl (1994) as well as studies in other species clearly defined endophyte-fed animals as having lower progesterone levels.

Few studies have accurately quantified the amount of toxin (ergot alkaloid) necessary to induce an effect on nutritional or reproductive status in horses. It is clear that infected fescue pastures elicit different effects in gestating mares from year to year. Concentrations of ergot alkaloids do fluctuate with management and environmental conditions. Work by Arns seems to suggest that dietary concentrations of ergovaline up to 308 ppb/kg total diet consumed has no adverse effects on reproductive performance in cycling mares.

Signs of fescue toxicosis have been seen in horses fed concentrations of ergovaline in excess of 325 ppb/kg total diet. More research is needed before one can recommend a specific concentration of ergot alkaloid that is safe.

It may be prudent for any horse breeder living in a region of the country where fescue grass is prominent to assess their pastures for endophyte infestation. Virginia pastures are well known for their prominence of tall fescue grass. Testing of pastures at ERC found that fescue grass made up 20-30% of the total grass population in the fields and 58 % of the fescue was indeed infested with the endophyte fungus.

Because consumption of certain levels of endophyte-ridden fescue has been shown to affect mares during the first 30 days and last 30 days of gestation, one should constantly be aware of exposure in pasture as well as in cut hay being fed. Apparently, ingestion of infected fescue has little to no affect on mares in the middle of gestation.

The present policy at Equine Reproduction Concepts is that no mare at our facility will be exposed endophyte-ridden fescue in cut hay or pasture form, during breeding, early gestation (first 60 days) or late gestation (last 45-60 days). If someone is concerned that their pregnant mare has been exposed to infected fescue during a vulnerable period, please consult a veterinarian for possible treatment. 


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