Research Accomplishment Reports 2007

Pregnancy Maintenance in Mares

K.J. McDowell
Department of Veterinary Sciences

 

Project Description

Pregnant mares grazing endophyte-infected (E+) tall fescue frequently incur reproductive problems such as extended gestation, dystocia, agalactia, and potentially death of the foal and/or mare. Horse farm managers seek to reduce/eliminate the amount of E+ fescue in their pastures, and many are currently using the selective herbicides Plateau or Cimarron for that purpose. However, the potentially harmful or endocrine disruptive effects of these herbicides to grazing broodmares and their fetuses are unknown.

This project tested the hypothesis that broodmares grazing pastures treated with Plateau or Cimarron will have increased incidence of fetal loss or newborn foal morbidity/mortality when compared with broodmares grazing untreated pastures.Two experiments were conducted.

In the first experiment entire pasture plots were broadcast sprayed with the herbicides, and in the second experiment fescue tufts and spots returning after the broadcast treatment were spot-sprayed. Each of these experiments was conducted in two consecutive years. Pregnant mares were placed onto the plots immediately after treatment, and then examined regularly for general health. Pregnancies were monitored by real-time ultrasonography, and blood samples were obtained for hormone analysis, clinical chemistries, and complete blood counts. Foals born to the mares were examined for general health and well-being, and blood samples were obtained for clinical chemistries and complete blood counts. Our results indicate that mares grazing pastures sprayed with Plateau or Cimarron at the rates recommended by the manufactures did not experience increased fetal loss or other general health problems compared to mares grazing non-treated pastures.

Impact

The per annum impact of the horse industry to the gross domestic product of the United States is approximately $112.1 billion, with $7.4 billion of that attributed to the horse breeding industry. There are approximately 30 million acres of fescue in the United States and approximately 80% of that estimated is to be E+ tall fescue. Although currently there is no estimate of the economic impact of grazing E+ fescue in horses, in cattle the economic impact is reported to be approximately $600 million annually. Adopting the practice of selective removal of fescue from pastures will provide more usable pasture acreage, will provide a more palatable and nutritious forage to livestock, and will reduce health risks and financial loss associated with animals grazing E+ tall fescue.