Fescue hay is a reasonable forage option for most horses, but it carries a serious risk for pregnant mares. The concern centers on a fungus that lives inside most tall fescue, which produces toxic compounds that can cause life-threatening complications during late pregnancy. For geldings, non-pregnant mares, and other working horses, fescue hay is generally safe, though it offers slightly less nutrition than popular alternatives like timothy or orchard grass.
How Fescue Compares Nutritionally
Tall fescue hay sits a step below timothy and orchard grass in energy and protein. It typically provides 5 to 9 percent crude protein compared to 7 to 11 percent for timothy or orchard grass. Its digestible energy ranges from 0.6 to 0.9 megacalories per pound, while timothy and orchard grass deliver 0.7 to 1.0. Calcium and phosphorus levels are essentially identical across all three. These differences are modest but meaningful: a horse eating fescue hay as its sole forage may need slightly more grain or a protein supplement to meet the same nutritional targets.
Palatability is another consideration. Research comparing horses eating tall fescue on pasture versus tall fescue hay found that hay intake was noticeably lower, around 1.74 percent of body weight per day in dry matter compared to over 2.2 percent on pasture. Digestibility dropped too, from roughly 53 to 55 percent on pasture down to about 44.5 percent for hay. Fescue hay can be coarser and less appealing than softer grasses, so some horses simply eat less of it.
The Endophyte Problem
The real issue with fescue isn’t its nutritional profile. It’s a fungus called an endophyte that lives inside the plant and produces a group of compounds known as ergot alkaloids. These compounds interact with receptors in blood vessels, causing them to constrict. The most important of these alkaloids is ergovaline. The original and still widespread variety of tall fescue, KY-31, is heavily infected with this endophyte, and the alkaloids persist in hay after cutting and drying.
For cattle, endophyte-infected fescue causes a well-known constellation of problems: poor weight gain, elevated body temperature, rough coats, and in severe cases, tissue death in the feet and tail tips (called “fescue foot”). Horses handle it differently. They dissipate heat through sweating far more efficiently than cattle, so they don’t develop the elevated body temperatures or the extremity problems cattle experience. Fescue foot has not been documented in horses. However, vasoconstriction has been measured even in non-pregnant mares, so the alkaloids are not completely benign in any horse.
Growing horses may see some impact. One trial found that yearlings grazing endophyte-infected fescue without grain supplementation gained weight more slowly than those on low-infection pasture, likely because they ate less and digested it less efficiently. When grain was added to the diet, the difference in growth rates disappeared. So for young, growing horses on a fescue-heavy diet, supplemental feed can offset the effects.
Why Fescue Is Dangerous for Pregnant Mares
The stakes change dramatically for broodmares in late pregnancy. Ergot alkaloids suppress prolactin, a hormone critical for milk production and normal foaling. Pregnant mares consuming endophyte-infected fescue can develop a condition called fescue toxicosis, and the consequences are severe: prolonged gestation (sometimes weeks beyond the normal due date), little or no milk production, thickened and retained placentas, difficult deliveries, and foals born weak or underdeveloped. One of the most dangerous outcomes is a “red bag” delivery, where the thickened placenta separates prematurely and the foal is essentially suffocated before it can be delivered.
Both mare and foal mortality rates increase with fescue toxicosis. This is not a subtle or occasional problem. It is the single most important reason horse owners worry about fescue, and rightly so.
Safe Ergovaline Levels
There is no universally agreed-upon safe threshold for ergovaline in a pregnant mare’s diet, partly because study designs and sampling methods vary. Extension services across different states set thresholds anywhere from 0 to 300 parts per billion (ppb). The University of Kentucky, which has done extensive work on this topic, uses 200 ppb as its general cutoff for late-term mares. That number is based on research showing that mares’ blood vessels begin to constrict noticeably at around 200 ppb of ergovaline in the total diet.
For non-breeding horses, average pasture and hay levels of ergovaline are typically tolerated without clinical problems. But if you’re feeding fescue hay to a pregnant mare, even “low” levels may be risky, and the safest approach is to eliminate it entirely during the last trimester.
Managing Broodmares on Fescue
The standard recommendation is to remove pregnant mares from all fescue, both pasture and hay, well before their expected foaling date. If removal isn’t possible or if exposure is suspected late in pregnancy, a medication that counteracts the prolactin-suppressing effects of ergot alkaloids can be given orally once daily starting 10 to 15 days before the expected foaling date and continued for up to 5 days after foaling if the mare isn’t producing enough milk. Your veterinarian can prescribe and dose this appropriately.
Replacing fescue hay with timothy, orchard grass, or a mixed grass hay during the last 60 to 90 days of pregnancy is the simplest and most reliable prevention strategy.
Novel Endophyte and Endophyte-Free Varieties
Not all fescue is created equal. In the 1980s and 1990s, endophyte-free varieties were developed to eliminate the toxicity problem entirely. They worked from a safety standpoint, but without the endophyte, the plants lost much of their toughness. Endophyte-free fescue doesn’t hold up well under drought, heavy grazing, or insect pressure, and stands tend to thin out and die sooner.
A better solution came with novel-endophyte (NE) fescue varieties. These contain a different strain of endophyte that still helps the plant resist environmental stress but does not produce the harmful ergot alkaloids. Grazing trials across horses, cattle, and sheep have confirmed that novel-endophyte fescue does not cause toxicosis. Ergot alkaloid concentrations in NE varieties are generally negligible. These varieties retain the hardiness and persistence of KY-31 without the toxicity, making them a practical option if you’re establishing or renovating horse pastures.
One exception worth noting: the variety BarOptima PLUS E34 has shown ergot alkaloid levels above the negligible range seen in other NE varieties, so it’s worth checking the specific cultivar before planting or purchasing hay.
Testing Your Hay
If you’re buying fescue hay and have pregnant mares, or you simply want to know what you’re dealing with, you can have hay or pasture samples tested for ergovaline concentration. The University of Kentucky Veterinary Diagnostic Laboratory offers this testing through its toxicology section.
For pasture sampling, the recommended approach is to walk the field in a zigzag or W-shaped pattern and cut handfuls of grass at grazing height from 20 to 30 randomly selected spots. Samples need to go on ice immediately after collection and stay cold until they reach the lab, shipped by overnight courier. Testing is most informative once plants have been actively growing for at least a month, so early summer is the ideal window. For hay, a representative core sample from multiple bales follows similar handling rules.
Kentucky horse owners can also enroll in the University of Kentucky Horse Pasture Evaluation Program, which provides ergovaline analysis alongside assessments of pasture species composition and estimated ergovaline intake for horses grazing each paddock.
Bottom Line for Feeding Fescue Hay
For geldings, non-pregnant mares, and mature horses in light to moderate work, fescue hay is a serviceable forage. It’s lower in protein and energy than timothy or orchard grass, so you may need to adjust grain or supplementation accordingly, and some horses eat less of it due to palatability. For growing horses, pairing fescue hay with adequate grain supplementation can offset any growth differences. The one absolute rule: keep endophyte-infected fescue hay away from mares in late pregnancy. If you’re unsure whether your fescue contains harmful endophyte levels, testing is straightforward and inexpensive relative to the cost of losing a foal.