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Mare Reproductive Loss Syndrome

Mare Reproductive Loss Syndrome Farm Survey Results

Maxwell H. Gluck Equine Research Center
University of Kentucky College of Agriculture
September 14, 2001

The goals of the 11-page Mare Reproductive Loss Syndrome (MRLS) farm survey were to:  identify factors with high association with MRLS early and late term abortions; identify protective factors which were in higher association with low or no loss farms compared to high loss farms; and determine areas needing further investigation.

133 farms participated in the survey:
66 farms were classified as early fetal loss (EFL)-only farms;
30 farms were classified as EFL and late term abortion (LTA) farms;
4 farms were classified LTA-only farms;
32 farms were control farms with low or no EFL or LTA; and
1 farm was EFL and not at risk of any LTA (had no mares in late pregnancy).
Farm managers were asked if they had excessive losses for EFL or LTA in comparison to previous years to make this classification.
The questionnaire was analyzed utilizing several statistical methods to crosscheck results.  The farm-based questionnaire evaluated farm management issues on the 133 farms.  A pasture-based questionnaire evaluated the pasture with the most mare abortion losses and a pasture with the least number of losses per farm.  A representative pasture holding at-risk mares was evaluated on low or no loss farms.  This resulted in a total of 212 pastures evaluated in the study.  Because of the low number of farms with only LTA, results apply to EFL and EFL/LTA farms.

An individual animal questionnaire was completed in August on six central Kentucky farms, which evaluated individual mare’s parity, age, status at 2001 breeding, medications and other factors.  This was to determine any differences between EFL mares and non-EFL mares on an individual animal basis.  Final analysis of this study will be forthcoming within the next weeks.

Within the farm and pasture questionnaires, and preliminary results from the individual animal questionnaire, four factors were associated with increased MRLS:

• breeding date in February 2001;
• moderate to high concentration of caterpillars in mare areas;
• presence of cherry trees around pastures; and
• having more than 50 mares on the farm.
Larger farm size can be explained by the likely presence of more barren and maiden mares on these farms, and therefore a larger percentage of mares being bred during February.

Only two factors were associated with a low incidence or no incidence of MRLS:

• absence of caterpillars, and
• feeding hay to mares in pastures.
The latter factor could be explained because mares eating hay were eating less grass in areas with high numbers of caterpillars.

Farm managers, veterinarians and horse industry members raised specific concerns, which were carefully analyzed.  An association between the following factors and MRLS was not detected in this survey:

• pasture composition (fescue, clover, orchardgrass, bluegrass or other grass types);
• mowing before, after or during the frosts of April 17 and 18, 2001;
• Fall 2000 or Spring 2001 fertilization with ammonium nitrate, urea, or any other fertilizer;
• treatment with lime in 1999, 2000 or 2001;
• manure spread on pastures;
• presence of surface water or source of drinking water;
• chain harrowing of fields;
• feeding grain to mares, type of grain fed to mares, source of grain (bags, bulk source, other), grain/hay contamination by domestic or wild animals;
• bedding type used;
• evidence in the mares’ environment with mice, rats, raccoons, skunks, coyotes, fox, deer or opossums;
• mares’ contact with cattle, sheep, goats, poultry, pigs, deer/elk, dogs or cats; and
• use of various dewormers.
Number of farms by caterpillar load
Caterpillar load EFL farm  Low/no EFL on farm
Moderate/heavy  93  21
Low 4 15
None 0 0
Total 97 36

One factor warrants further investigation and consideration.  While nearly all farms observed water fowl at least sometimes, a higher percent of farms with EFL reported observing waterfowl “often.”  It is strongly emphasized that this is in no way an indication to eliminate waterfowl from farms.  Rather, this may indicate that some environmental factor, which is associated with waterfowl presence, is also associated with the syndrome.  The frequent observation of waterfowl on farms with losses deserves further investigation to fully understand what part, if any, they may play in the syndrome.

This in-depth, three-tiered survey was only possible by the outstanding cooperation of farm owners, managers and their staff, the survey team of state and federal veterinarians and technical staff, volunteer veterinarians and trained individuals.  USDA veterinarians on the federal and state levels were critical in providing the expertise needed in survey development, data entry and analysis.

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