In the latest update on Mare Reproductive Loss Syndrome, researchers at the University of Kentucky report the evidence continues to point toward cherry trees and a caterpillar infestation this spring as the likely causes of the problem. Research also has proven negative for hemlock plants as the source of the late-term abortions and foal losses.

The researchers report that an epidemiological survey has been conducted of 133 central Kentucky farms, representing 89% of the 150 farms initially contacted. The survey was compiled by on-site visits to each farm to ensure the “quality of data in the complex 11-page questionnaire,” the briefing stated. The farms surveyed had more than 17,000 horses on their premises as of April 1 and included the Thoroughbred, Standardbred, American Saddlebred, and Morgan breeds.

While the data has been verified and entered into a computer, UK reported “an in-depth analysis of this data is very detailed and is not a fast process.”

However, preliminary analysis of pasture data has revealed several individual risk factors. Those risk factors, which were higher in pastures with affected mares when compared with low or no losses in mares, include:

  • Cherry trees in and around pastures
  • Cherry tree seedlings in the pasture
  • Deciduous trees stripped of leaves in pastures
  • Moderate to heavy caterpillar presence.

Factors which were not significantly higher in pastures with affected mares include:

  • Pasture composition of 40% or greater of any of the following grasses: fescue, orchard grass, bluegrass, clover or other grasses
  • Clover at 10% or 20% in pastures
  • Chain harrowing
  • Feeding supplemental hay
  • Spring pasture fertilization
  • Presence of deciduous trees (non-cherry) in or around pastures
  • Surface water in pasture