The cause or causes of mare reproductive loss syndrome are still a mystery, but that hasn't lessened interest in the topic. During an informational session Monday, new questions were raised about circumstances surrounding the outbreak during last year's breeding season.
One of the evening's most riveting presenters was Dr. Stuart Brown, a Lexington-area veterinarian with Hagyard-Davidson- McGee. Brown has a large reproductive practice and believes Central Kentucky's broodmare population, particularly the approximately 3,000 who lost 2002 foals early into their pregnancies, could hold the answers.
Brown said he conducted uterine cultures on mares who experienced early fetal loss after seeing irregular occurrences in pregnant mares last May. He found a majority of those samples contained one of two types of bacteria: Alpha Streptococcal organisms or Actinobacillus sp. organisms. He estimated 65% of his samples showed Alpha Streptococcus and 20% returned Actinobacillus sp.
These findings mirrored those from Dr. Mike Donahue, supervisor of the bacteriology lab at the University of Kentucky's Livestock Disease Diagnostic Center where nearly all of the 500 late-term fetuses brought to the center in 2001 were examined. Donahue found 70% of the pathological tissues from the lung or umbilical cords yielded one or both of the same bacteria.
"These are two organisms you don't expect in that area," said Brown. "In my opinion, 70% is significant."
After Donahue isolated the bacteria, he said he froze approximately 380 samples for further study. Further study could identify the species and source of these bacteria. It is possible they normally occur in a horse's system, but changed their makeup or location in response to the affects of MRLS. Donahue has submitted grant proposals to two organizations to support more research he hopes to continue this spring.
One of three studies currently funded by the Grayson-Jockey Club Foundation and involving MRLS has progressed to a preliminary discussion and report phase. Dr. Dee Cross and Ph.D. candidate Sam Gray will informally present their findings at Clemson University on Feb. 8. Gray said the study of 38 pastures in Central Kentucky has shown a correlation between poisonous hemlock and effects of MRLS.
"The pastures that had problems had poison hemlock and also showed evidence of consumption," said Gray. Of the 28 pastures studied with MRLS losses, 27 had hemlock presence confirmed. In 10 pastures without problems, there was no evidence of consumption.
Gray and Cross have applied for more funding to complete the study by testing the effects of hemlock on 14 pregnant mares. The plant has been shown to cause abortion in other species.
The numbers are compelling, but Dr. Roy Smith, supervisor of toxicology at the diagnostic lab, said hemlock is "highly improbable as a cause." Smith said he tested 50 of the 500 fetuses examined at the center in 2001 for hemlock and "we found nothing."
"Poison hemlock is everywhere," said Smith. "Why should it suddenly be toxic this year? A frost could make poison hemlock palatable, but I have not read any evidence that it was grazed at all."