Horses and tall fescue pasture can be good, bad, or just plain ugly. Tall fescue is a durable, high yielding cool-season grass with many desirable characteristics for a pasture grass. When we use it with horses, however, we must be very careful to use the right kind.
Most older, traditional fescue varieties contain an internal fungus, or endophyte, that produces chemicals that help plants resist insects and diseases and make it more durable, which is good. This helps fescue survive abuse by grazing horses, which might make fescue the best choice for pastures used as exercise lots or that receive a lot of close, continuous grazing.
One problem, though. These endophyte chemicals also cause severe reproductive problems for horses. Mares can abort or have stillborn foals. The gestation period is longer and foaling problems are more common for mares grazing endophyte-infected fescue. After foaling they may fail to produce milk and they can have trouble conceiving again.
Obviously, avoid endophyte-infected fescue if you plan on breeding your horses. But this doesn’t mean avoiding fescue completely. Several new varieties do not have endophytes, so they also don’t have the chemicals that cause these reproductive problems. These endophyte-free fescues are safe to use with breeding stock. Endophyte-free fescues may not be quite as durable as their problem-causing cousins, but they still will persist in well-managed pastures.
So, to summarize, use endophyte-infected fescue where durability and persistence are most important. But when breeding stock are involved, only use endophyte-free varieties. Your horses will stay healthy and you’ll sleep better at night.