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Fescue poses threat to pregnant horses
By Allison Matthews
MISSISSIPPI STATE -- Lush, green fescue may look ideal for livestock before summer grasses are available, but beware of the invisible threat for pregnant horses lurking inside the winter grass.
Peter Ryan, assistant professor of animal science at Mississippi State University, said fescue is a common forage grass for horses and other livestock in the southeastern United States, but it is frequently infected with a strain of endophyte. The fungus is not harmful to the grass, but it can be hazardous to grazing animals and their offspring.
"The endophyte-infected grasses can cause negative effects on other livestock, such as in cattle, but it seems to cause the most serious problems in broodmares," Ryan said.
Horses who have grazed on infected fescue develop fescue toxicosis, a condition which may suppress important hormones like serum prolactin and relaxin. These deficiencies during pregnancy can lead to a high incidence of foal immaturity and mortality. "Mares that have grazed enough infected fescue to develop the toxicosis may have placental thickening, prolonged gestation, difficult deliveries and little or no mammary gland development, which leads to poor milk production," Ryan said.
He explained that each individual symptom can be a serious problem, but many mares experience multiple symptoms as a result of the endophyte. Mares may carry their foal for much longer than a normal term, resulting in a larger foal and harder delivery.
Dr. Michael Brashier, associate professor at MSU's College of Veterinary Medicine, said the foals delivered after a longer gestation period may be larger, but they are usually weaker.
A mare's lack of hormones to stimulate mammary production poses a serious threat to newborn foals. Brashier said a foal gets vital antibodies from its mother's milk during the first day after birth.
"Other animals absorb many antibodies before birth through the placenta, but foals count on the antibodies from their mother's first milk," Brashier said.
Ryan said horse owners can guard against the problems associated with fescue by removing pregnant mares from endophyte-infected pastures early in the third trimester. Drug therapy is available if owners cannot remove their broodmares from infected fescue, but accurate records of breeding dates must be kept to ensure the drugs are given appropriately.
Ryan said MSU has participated in a study in collaboration with Pennington Seed, Inc., which suggests a new variety of endophyte-infected fescue will not cause the negative effects in grazing animals. He said farmers can have their grass tested for toxicity by contacting a local Extension agent. Pastures that contain endophyte should not be used as primary grazing sites during spring's rapid growth when most mares are in the last trimester of pregnancy.
For more information, contact: Dr. Peter Ryan, (662) 325-2802 or Dr. Michael Brashier, (662) 325-1448