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Mare Reproductive Loss Syndrome

Following is a statement sent to State Veterinarians June 11, 2001
TO:  State Veterinarians

DATE:  June 11, 2001

SUBJECT:  Mare Reproductive Loss Syndrome - Update

Dr. Don Notter, Kentucky State Veterinarian, has asked that I provide to you the latest information regarding the Mare Reproductive Loss Syndrome (MRLS) occurring in Kentucky's equine population. While the occurrence of MRLS
appears to be declining, the pace of the investigation has not diminished. You can find links to the most current information regarding the investigation at

We are receiving reports from practitioners suggesting that some pregnancies continue to be lost.  In addition, cases of pericarditis and unilateral eye problems are continuing to occur in Kentucky. Approximately 50 cases of each condition have been identified to date involving a wide age range of horses and breeds. Numerous tests have been performed and further tests are underway to identify the cause of these conditions and clarify the link to MRLS.

On Wednesday, May 30, veterinarians, state and federal animal health employees, and qualified volunteers began surveying over 150 equine farms in multiple areas of the state.  A copy of the questionnaire can be found on the Internet at Once completed this surveying will provide more than 48,300 pieces of data that will need to be analyzed. With the majority of the surveys having now been completed, we are in the process of entering the information into a database.  This type of detailed information takes time not only to be accurately entered, but for the multi-factorial analysis to be completed as well.  Results of the survey will be released to the industry after a thorough analysis has been completed. It is the goal of the investigating group that with the results from the survey we will be better able to identify risk factors and provide supportive information to the diagnostic team.

While field observations and clinical data discovered to date continues to suggest the involvement of cyanide, the investigating team does wish to again reemphasize it is not excluding any possibility.  Detailed investigations are underway to prove or disprove the possibility of cyanide as the cause of MRLS. In addition, the investigation of other possible causes including mycotoxins, fungal endophytes, phytoestrogens, chemical compounds and infectious agents is still ongoing, although results to date provide no evidence they are involved in the cause of MRLS.

We will keep you updated as any new information becomes available.

E.S. Rusty Ford
Equine Programs Manager

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