At first, tall fescue grass sounds too good to be true. While it's hardy, easily established and tolerates close grazing, tall fescue grass can also be poisonous to broodmares and their foals.
What's the Danger?
Most fescue grass in the United States is infected with a fungus that produces alkaloids toxic to animals. The major effects of the toxin are seen in broodmares, with problems occurring late in gestation.
Fescue toxicity can cause abortion at or around the time a mare is expected to foal. Conversely, fescue toxicity can cause a mare to carry a foal for a month or two longer than normal. This prolonged gestation results in a larger foal and more difficult birth, a condition called dystocia.
Fescue toxicity can result in placental abnormalities such as a thickened placenta. Retained placentas occur in more than 50 percent of broodmares afflicted with fescue toxicity.
Danger to the Foal
Many broodmares with fescue toxicity exhibit agalactia, failure to develop normal mammary glands. This means the mare produces little or no milk for her foal.
Broodmares with fescue toxicity have decreased levels of prolactin and progesterone. Some may not exhibit typical signs of foaling.