CEM: Breeding Farm Precautions

The problem of contagious equine metritis (CEM) has not gone away. In fact, it has become more confusing as the weeks have progressed since a "CEM-like organism" was found in a Mammoth donkey jack in California in December 1997. In a separate and unrelated incident, a second CEM-like organism was recovered from a jack in Kentucky in January 1998. The two jacks had no known association or relation, according to correspondence from the USDA. (See The Horse of March, 1998, page 34.)

Since that time, one mare (located in Oregon) bred to the California jack has tested positive for the CEM-like organism.

In Kentucky, two Standardbred nurse mares which were undergoing examination to qualify as post-import breeding test mares have tested positive after being bred to the initial jack. There have been two other stallions (a paint horse and another jack) and two other females in Kentucky that thus far have tested positive and which had resided on the same owner's premises as the original jack and mares which tested positive for the CEM-like organism.

What is known is that while there has been no historical contact between the California and Kentucky animals, the “CEM-like” organisms cultured from those equids are similar. The organism is different in enough ways that it is being considered a “subspecies” of CEM until more tests can be performed.

There is some thought on the part of researchers that the current organism could be common in some donkeys or mules and have no contribution to reproductive problems. However, more research needs to be done to determine whether the new organism is able to produce disease.

CEM is a highly contagious venereal disease caused by the bacteria Taylorella equigenitalis. It can cause short-term infertility in mares, infection and inflammation in the mare's reproductive tract, and rarely abortion.

There are questions of whether grade or nurse mares could be carrying this organism without showing any signs of illness (which has been the case thus far). If so, then farms which use these types of mares as surrogate mothers for foals should take certain precautions to ensure they are not bringing an unknown organism onto their properties. The same is true of farms which have new teaser stallions, those which lease teasers for the breeding season, or those which board out their teasers during the off season. While the contagiousness of this new organism has not been determined, the normal CEM organism can be passed from horse to horse not only through breeding, but through improper hygiene or management.

All breeding operations should be careful until more information becomes available and researchers are better able to establish the prevalence and significance of infection with this “CEM-like” organism. Breeding operations also should be aware of the potential for Taylorella equigenitalis, the causative agent for CEM, to be imported from Europe through Warmbloods or sport horses.

Following are recommendations compiled from the latest facts known by researchers and veterinarians dealing with CEM and the CEM-like organism.

  • All nurse mares and stallions which have been off the property should be isolated and tested for CEM, especially if they have been on a farm with donkeys or mules or Warmblood stock.

  • Stallions bred to "grade" test mares early in the season should have that mare tested for evidence of CEM.

  • If horses are used for breeding, three sets of swabs should be taken from the stallion or mare at intervals no less than seven days, and the first mare bred by the stallion should be tested 20-30 days post-breeding.

  • The swab sites in the mare should include the clitoral sinuses and fossa, the cervix (if possible), as well as any vaginal exudate. Endometrial/cervical swabs should be taken during early estrus.

  • In the stallion, swabs should be taken from the urethral fossa and sinus, distal urethra, external surface of the penis, and prepuce. A sample of the pre-ejaculatory fluid also should be tested.

  • If a mare's blood is sampled to test for evidence of recent exposure to the CEM organism, this should be done between 20 and 30 days after breeding to allow adequate time for development of serum antibodies.

  • Care should be taken to thoroughly disinfect equipment used in breeding.

  • CEM is considered a foreign animal disease. Most states require equids with clinical signs of CEM or with known exposure to CEM be reported immediately to the state veterinarian.

About the Author

Tim Brockhoff

Tim Brockhoff was Staff Writer of The Horse:Your Guide to Equine Health Care from 1995 to 1999. His degree is in Agricultural Communications from the University of Kentucky, and his equine experience is with American Saddlebreds.

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