Tall Fescue: Potential Problem for Pregnant Broodmares

Tall fescue is a variety of cool-season grass that is found throughout Pennsylvania and the United States. It is well adapted to low-pH soils, is drought resistant, and can tolerate high stocking densities. Due to these traits, tall fescue is highly sought after as a pasture grass. There can be, however, a downside to tall fescue, particularly for pregnant broodmares.

Certain varieties of tall fescue are infected with the fungus Neotyphodium coenophialum (formerly known as Acremonium coenophialum). The fungus is advantageous to tall fescue in that the fungus provides protection against certain insects and drought and heat. The fungus produces ergot alkaloids, and it is these alkaloids (particularly ergovaline) that can cause harmful physiological effects in pregnant broodmares. Tall fescue known to have Neotyphodium coenophialum is known as endophyte-infected tall fescue. The amount of ergot alkaloids on a given pasture will vary depending on the time of year, the amount of fertilizer present, and simply plant variation.

Pregnant broodmares that consume endophyte-infected tall fescue are at risk for developing fescue toxicosis. The symptoms in mares of fescue toxicosis include prolonged gestation, abortions, stillbirths, thickened placentas, low conception rates, weak foals, increased risk of newborn foal death, dystocia, and low/no milk production (known as agalactia). You can't tell just by looking at the tall fescue if it is infected; the grass must be tested.

Broodmares in late pregnancy are the only horses that are known to suffer ill effects from grazing endophyte-infected tall fescue. Non-breeding stock have not been shown to date to suffer adversely from grazing endophyte-infected tall fescue. Research has also shown no adverse effects on stallions and their reproductive function when they graze endophyte-infected tall fescue.

So, what can be done to help our pregnant broodmares? It is recommended that if your pasture does have endophyte-infected tall fescue, then you should remove pregnant broodmares from the pasture 60-90 days prior to foaling. Another option is to talk with your veterinarian about treating your mare with domperidone, which can help relieve most fescue toxicosis symptoms.

If you have enough acreage and can devote the time and money, then renovating your pastures to remove the endophyte-infected tall fescue is another management option. You can remove the tall fescue with an herbicide and choose other cool-season grasses to plant, or you could plant endophyte-free tall fescue. Again, this process can be costly and take several years, so it might not be the best solution for everyone. It can be difficult to completely remove all endophyte-infected tall fescue from a pasture. Additionally, if you have a mix of cool-season grasses in your field, be sure to identify what percent is actually tall fescue. If the tall fescue is a small minority of the grass in your field, then there is less risk for your broodmares, and perhaps the best management strategy is to simply remove them from the field 60-90 days prior to foaling.

In summary, fescue toxicosis can have serious detrimental effects on pregnant broodmares. If you are unsure if your pasture contains tall fescue, contact your local extension office, who can help identify the grass. If it is confirmed that your pasture contains tall fescue, then samples should be sent to a forage lab to be tested. Samples should be taken when the plant is growing rapidly (typically early summer and fall, though this will depend on the weather and region), to ensure you do not get a false low reading on the endophyte analysis. If you breed mares on your farm, and have tall fescue, be sure to discuss with your veterinarian the risks of fescue toxicosis and the best management strategy for your farm.

Listed below are a few laboratories that analyze fescue for ergot alkaloids/endophytes:

• Agrinostics Ltd. Co.
• Oregon State University Endophyte Service Laboratory
• Cumberland Valley Analytical Services

Additional Resources

Fayrer-Hosken, R., Heusner G., Hill N., Caudle A. 2008. Review of effects of fescue grass ergot alkaloids in the horse and preliminary study on effect of fescue grass ergot alkaloid in the stallion. J. Equine Vet Sci. 28 (666-671).

Fayrer-Hosken, R., Hill N.S., Heusner G.L., Traylor-Wiggins W., Turner K. 2013. The effects of ergot alkaloids on the breeding stallion reproductive system. Equine Vet J. 45 (44-47).

Cross, D.L. The Grass Isn't Always Greener: Symptoms and Treatments of Fescue Toxicosis.

Hall, M. 2008. Tall Fescue.