Breeders know the danger equine fescue toxicosis can pose for pregnant mares. Tall fescue is a cool season, perennial grass prevalent in the eastern and central United States that often becomes infected with endophytic fungus, primarily ergovaline. Mares that graze on endophyte-infected fescue in their last month of pregnancy develop prolonged gestation, lack of or low milk production, dystocia (difficult birth), malpresentation of the fetus, premature placental separation (“redbagging”), tough and thickened placentas, weak and dysmature foals, and foal and mare mortality.
The endophyte fungus is difficult to eradicate because it is symbiotic. It lives within the fescue plant and actually makes the tall fescue hardier. Plants that are infected survive adverse conditions, while healthy plants die. The only way to kill the endophyte is to kill the plant.
Forage specialists developed endophyte-free tall fescue to address the problem through pasture management. The infected tall fescue must be destroyed with multiple applications of herbicide and the pastures reseeded with endophyte-free fescue. But infected fescue eventually can creep back into the endophyte-free field when seeds blow in from neighboring, uncontrolled pastures. Pastures also may be infected simply by a farmer feeding his pasture horses an infected bale of hay that contains seedheads. Similarly, livestock fed hay containing infected seeds will pass the seeds through their manure and reinfect their pastures. Birds also can spread infected seeds through their droppings.
More frustrating is that even if all efforts to keep a pasture endophyte-free are successful, healthy plants are less hardy than infected ones and usually die off in four or five years under good management. Nimblewill, a useless weed that competes for the same soil as fescue, can sometimes take over to ruin the pasture on farms located in western Virginia, West Virginia, Kentucky, southern Ohio, Indiana, and Illinois.
Fortunately, forage experts are working on a solution.
A novel solution
“Researchers in New Zealand figured out a way to get beneficial endophytes into the fescue that help the plant survive but don't produce the toxins harmful to livestock,” said Dr. Ray Smith, a forage specialist at the University of Kentucky. “The beneficial endophyte fescue has been studied at UK's Maine Chance Farm to see if it is safe for pregnant mares, and we haven't seen any problems. It's quite a breakthrough because it allows us to use fescue without having to worry about the toxins, whether you are using it for pasture or baling it for hay.”
Several varieties of beneficial endophyte fescue are available, including Texoma MaxQII, Martin II Protek, and Lacefield MaxQII. Another variety, Baroptima Plus E-34, contains low levels of ergovaline and is not suitable for pastures with pregnant mares.
Smith explained how to eradicate infected fescue and replace it with beneficial endophyte fescue.
“You have to mow the infected fescue before it goes to seed,” he said. “Most seed from the previous year would be gone, so you don't have to worry about that. Then a couple of sprays of Roundup, spread over six weeks, will do it. You don't have to work the field with major implements.”
Smith said the ideal time to seed with beneficial endophyte fescue in Kentucky and neighboring states with similar climates is late August to mid-September, unless temperatures soar into the high 90s.
“Often our Octobers are dry, and the seed doesn't germinate until it's wetter in late October and early November, then it doesn't have time to establish to make it through the winter,” he said.
In states with warmer temperatures, such as Georgia, Alabama, Mississippi, and eastern Texas, seeding can be as late as October or early November. Smith advised consulting your local extension service for its recommendations.
Ideal spots to seed with beneficial endophyte fescue are along streams, around ponds, and in wet areas of a pasture that typically are overrun with weeds because of the wet soil.
“It is also quite hardy for droughts,” Smith said. “So if you have shallow soils, with bedrock close to the surface and it's hard to get orchardgrass and bluegrass to survive, tall fescue would be the very best grass for those areas.”
Once the beneficial endophyte fescue is established, farmers should submit samples for an ergovaline assay every two years to assure infected fescue has not crept back into the field. This specialized testing is required because other fescue assays only will determine if endophytes are present and do not differentiate between toxic endophytes and beneficial endophytes.
In Kentucky, the university's Veterinary Diagnostic Laboratory offers this special assay service as part of its Horse Pasture Evaluation Program. Contact your local extension office to see if it offers similar testing.
For breeders who are still concerned about fescue toxicosis, treatment of pregnant mares with domperidone can be initiated within 15 days of the mare's expected foaling date if she is to be left on tall fescue, and 10 days if she is to be removed from the pasture. It is administered like a paste dewormer: four to six ccs. (depending upon the mare's weight) of a brown, molasses-based slurry given by oral syringe.
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