Fescue Toxicosis in Broodmares: Signs, Risks & Solutions

Fescue Toxicosis in Broodmares: Signs, Risks & Solutions

Tall fescue (Festuca arundinacea) infected with the endophytic fungus Neotyphodium coenophialum is one of the leading pasture-related threats to broodmare reproductive success. Removing mares from infected fescue pastures at least 60–90 days before their due date is the single most impactful management step you can take in 2025.

What Is Fescue Toxicosis and Why Does It Matter?

Tall fescue covers an estimated 35–40 million acres across the United States, and surveys consistently show that 80–90% of established stands carry the endophyte fungus. The fungus produces ergot alkaloids — primarily ergovaline — that persist throughout the plant year-round, with peak concentrations in stem bases and seed heads during late spring and summer.

For broodmares, these alkaloids interfere with dopamine and prolactin signaling, disrupting the hormonal cascade that governs late pregnancy and parturition. The result is a cluster of clinical signs collectively called fescue toxicosis syndrome.

How Do You Identify Endophyte-Infected Pastures?

Visual inspection alone cannot distinguish infected from endophyte-free (E-) tall fescue — the grass looks identical. Reliable identification requires one of the following:

Laboratory Testing

• Immunoblot or ELISA test kits (e.g., Agrinostics Quick Test) detect endophyte proteins directly in fresh leaf tissue. Results in 15–30 minutes on-farm.
• Microscopic examination of seed or leaf sheath tissue by a forage laboratory confirms fungal hyphae presence.
• Send samples to your state extension forage lab — most charge $20–$50 per sample and return results within 5–7 business days.

Sampling Protocol

1. Collect 20–30 tillers from across the pasture (not just one area).
2. Sample from the lower leaf sheath, not the blade tip.
3. Keep samples cool and submit within 48 hours.
4. Test in late spring or early fall for highest accuracy.

Risk Indicators Without Testing

While not definitive, the following increase suspicion:

• Pasture established before 1990 (endophyte-free varieties became commercially available in the late 1980s)
• Dense, dark-green, waxy leaf appearance that persists through drought
• Located in the transition zone (Virginia to Kansas, Missouri to Georgia)
• History of reproductive problems in broodmares on that field

What Are the Clinical Risks in Late Gestation?

Fescue toxicosis produces its most serious consequences in the final trimester (days 240–340 of gestation), when fetal growth is maximal and the mare’s body is preparing for parturition.

The mechanism behind these effects is well-characterized: ergovaline competitively inhibits dopamine D2 receptors in the pituitary, suppressing prolactin release. Prolactin is essential not only for milk production but also for the normal pre-foaling endocrine events that trigger cervical softening and placental separation.

Why the Third Trimester Is Critical

Veterinary guidelines consistently recommend removing broodmares from tall fescue fields by day 240–270 of gestation (approximately months 8–9). Colorado State University’s Dr. Jennifer Hatzel notes that the third trimester represents the period of maximal foal growth and the window where increased mare nutrition and careful pasture management are non-negotiable.

Once a mare has been on endophyte-infected fescue through the third trimester, some hormonal disruption may already be established. Acting at day 300 is better than not acting at all — but acting at day 240 is far better.

How Long Before Foaling Should Mares Be Removed?

The research consensus supports a minimum of 60–90 days off infected fescue before the expected foaling date. Some reproductive veterinarians recommend extending this to the entire last trimester.

• 60 days minimum: Allows ergovaline to clear from the diet and partial prolactin recovery.
• 90 days or more: Associated with significantly lower rates of agalactia and prolonged gestation.
• Throughout pregnancy: Ideal for high-value mares or those with previous fescue-related problems.

Keep in mind that ergot alkaloids can also accumulate in hay cut from infected fescue pastures. Testing hay is just as important as testing standing pasture.

What Are the Mitigation Options?

1. Pasture Removal and Transition

The most reliable strategy. Move mares to:

• Endophyte-free tall fescue (E- varieties such as MaxQ)
• Orchardgrass, timothy, or bluegrass-dominant pastures
• Drylot with tested hay from non-fescue sources

2. Pharmacological Intervention: Domperidone

Domperidone (a dopamine antagonist) is the most commonly used veterinary treatment when pasture removal is not possible or when signs of toxicosis are already present. It restores prolactin levels and has been shown to:

• Improve udder development and colostrum production
• Reduce the incidence of agalactia
• Help normalize foaling timing when administered 10–14 days before expected parturition

Always consult your veterinarian for dosing — typical protocols involve daily oral administration beginning 10–30 days before the due date.

3. Pasture Renovation

For long-term management of breeding farms, consider:

• Killing and reseeding with novel endophyte or endophyte-free fescue cultivars
• Overseeding with legumes (clover, alfalfa) to dilute fescue intake, though this provides only partial protection
• Rotational grazing to reduce fescue consumption during highest-risk periods

4. Monitoring High-Risk Mares

Mares that have been on infected fescue should be monitored closely as foaling approaches:

• Track udder development starting 2–4 weeks pre-foaling
• Use milk calcium testing (levels above 200 ppm indicate foaling within 48 hours)
• Consider twice-daily temperature monitoring
• Have your veterinarian on call for foalings from mares with fescue exposure history — dystocia and foal maladjustment syndrome are more likely

Breedio lets you log pasture changes, track gestation day-by-day, and set custom alerts for high-risk windows — so you never miss the removal deadline. See the full feature set or start tracking your mares today.

Does the Season Affect Ergovaline Levels?

Yes — and this has direct implications for management timing:

Stem bases and seed heads carry the highest alkaloid concentrations. Avoiding fescue during the seed-head stage (typically May–June in temperate zones) is especially important for late-gestation mares.

What About Hay and Hay Cubes From Fescue?

Mares managed on clean pastures can still be exposed through:

• Hay bales harvested from infected fescue fields
• Fescue hay cubes or pellets included in commercial forage products
• Straw bedding from fescue crops (minor risk, but worth noting for sensitive mares)

Request endophyte testing on any purchased fescue hay destined for broodmares in their final trimester. Many forage testing laboratories include endophyte screening as an add-on to standard forage analysis.

Key Takeaways for the 2025 Breeding Season

• Test your pastures using ELISA kits or forage lab analysis before mares are bred.
• Remove mares no later than day 240 of gestation (90 days before expected foaling).
• Test hay from fescue sources before feeding to late-gestation mares.
• Discuss domperidone with your veterinarian if removal is delayed or signs of agalactia appear.
• Monitor udder development and milk calcium closely on any mare with fescue exposure history.
• Renovate long-term by transitioning to novel endophyte or endophyte-free pasture varieties.

Fescue toxicosis is almost entirely preventable with proactive management. The cost of a pasture test or a pasture transition is trivial compared to the cost of a dystocia, a maladjusted foal, or a mare with no milk at foaling time. Use Breedio to set gestation milestones and removal reminders so these critical windows don’t slip through the cracks.