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Fescue: Why Worry?


2014/03/07

By Leigh Ballard

Fescue grass has some advantages as a forage, bit we worry about it because it also can have some serious detrimental effects, especially for broodmares. If exposure to fescue can cause economic and emotional loss, is it worth the risk?

Fescue grass is present in pastures in all areas of the mid south, and about 80% of pastures in Tennessee include fescue. Tall Kentucky-31 fescue is a widely used grass because it is a hardy, cold-tolerant, and fast growing. It tolerates drought and heavy grazing, provides good nutrition, and stabilizes soil against erosion. Its many attributes make it a good grass for relatively easy pasture management. However, the attributes that give fescue its popularity are caused by the presence of an endophytic fungus in the grass. This fungus is the problem that makes the grass dangerous for broodmares.

The word “endophytic” refers to an organism, in this case, a fungus Neotyphodium coenophialum, which lives within the cells of the grass. The relationship between the plant and the fungus establishes favorable survival characteristics for the plant, such as cold tolerance, disease resistance and a sturdy root system. A substance secreted by the endophyte, an alkaloid toxin, is the agent that affects the late stages of pregnancy in mares. This toxin is present in the fescue grass seeds, and in the actively growing parts of the plants, so typically the strongest threat of ingesting the toxin is present usually about the same time as a mare’s last stages of pregnancy. 

The toxin interferes with certain hormone expression. Relaxin, which dilates the cervix and allows pelvic joints to spread, is one hormone that is adversely affected. Therefore, fescue toxicity often causes prolonged pregnancies well over the typical 11 months, which terminate with stillborn foals. Dystocias, or difficult births, are another common result of fescue toxicity. The placenta is thick and cannot rupture properly; placenta and fetus try to deliver simultaneously. These abnormal “red bag” births are difficult and often result in the death of the foal and/or the mare.

Prolactin, the hormone responsible for signaling the mare’s body to begin milk production, is another hormone which is adversely affected. Agalactica is the condition in which mares fail to begin milk production in preparation for the foal’s arrival. Typically the affected mares fail to “bag up,” and when the foals are born, the mare is agalactic or without milk, or are hypogalactic with little milk.

Removing broodmares from fescue pasture is the best solution for avoiding these potential problems. The last 90 days of pregnancy are the recommended time period for taking a mare off fescue. This management strategy is not always convenient, but is the best way to ensure delivery of a healthy foal. Removing the mare to a paddock or dry lot and feeding non-fescue hay along with a balanced concentrate, will eliminate the risk of fescue toxicity. If an owner is late to realize the risk, or the mare came into the owner’s care already within this 90 time period, removing the mare from fescue later than 90 days is far better than not removing her at all.

Fescue has been shown to cause problems in early pregnancy as well. Mares that graze fescue pastures often have early embryonic deaths (EED), usually during the first 40 days of confirmed pregnancy. Studies at Mississippi State University show a number of mares that were confirmed pregnant at 2-3 weeks were not pregnant at re-examination at 40 days. Fescue problems seem to lessen after the 40-day mark, and mares confirmed in foal at 40 days are likely to carry the foal to term.

Re-breeding problems due to fescue toxicity can be avoided with fescue management. Besides the negative economic effect of losing a future foal, the rebreeding schedule can be compromised. The mare might not re-cycle to be bred again, or a very late foal may be the result.

New varieties of “fungus free” fescue have been developed which are better grazing choices for broodmares. Consult with your county extension agent for recommended varieties.

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