While there has been speculation that several cases of mare reproductive loss syndrome (MRLS) happened in Washington state during the spring of 2003, the number of accessions to the state’s diagnostic lab doesn’t uphold that theory. Charles Leathers, DVM, PhD, professor of pathology at the Washington Animal Disease Diagnostic Laboratory, said, “From our perspective, we have not seen the numbers to make an association with MRLS. We’re not minimizing any farm’s losses, but we are not seeing an increase in the number of successions (animals/fetuses submitted for necropsy) to the lab.”

Leathers said Kenneth Feigner, DVM, a Western Washington veterinarian who made the MRLS claims in an article that appeared both in the Washington Thoroughbred and DVM Magazine, has submitted only one fetus to the lab in the last three years. “No cause was found for that abortion, but we do know what we are looking for,” said Leathers, who has worked with Lynn Harrison, DVM, head of the Kentucky Livestock Disease Diagnostic Lab on this theory of MRLS in Washington.

Leathers said samples of the caterpillars were sent to Harrison for testing. The first question was whether the caterpillars were Eastern or Western tent caterpillars, and whether there were any possible toxic fractions.

The MRLS seen in Kentucky and surrounding states in 2001-2002 is thought to be linked to Eastern tent caterpillars (ETC). The problem in Washington was suggested to be linked to Western tent caterpillars (WTC), a close relative