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