Contagious Equine Metritis Case Could Impact Horse Transport

State and federal agriculture officials announced Dec. 16 that a Quarter Horse stallion standing at stud in Kentucky has tested positive for contagious equine metritis (CEM). As the United States is considered free of the highly contagious venereal infection (which can cause infertility and abortions, or can exist and spread subclinically), this raises two major issues: where did it come from, and will it affect equine transport, either interstate or internationally?

According to Rusty Ford, equine programs manager in the office of Kentucky State Veterinarian Robert Stout, DVM, the affected stallion is a 16-year-old Quarter Horse who came to a farm in Kentucky (the identity of which he cannot legally reveal) in February 2008, after being collected for breeding via artificial insemination in Texas. Twenty one other stallions, all Quarter Horses, stood at the Kentucky facility. The CEM causative organism, Taylorella equigenitalis, was discovered when the affected horse was examined prior to his semen being shipped to the European Union. All but eight of the stallions had shipped to other farms this summer, following the conclusion of the 2008 breeding season. One stallion had moved to another farm within Kentucky and the rest moved out of state.

USDA officials and state veterinarians are working to locate these horses, as well as 44 mares that were inseminated with semen from these stallions, for testing. Preliminary information puts the horses' owners in 18 states, but whether the horses are currently located in those states is one of the questions officials are working to answer.

In 1978, an outbreak of CEM in Kentucky shut down the Thoroughbred breeding season, costing the industry an estimated $1 million per day.
Finding CEM-positive horses is not simple; T. equigenitalis can be present, undetected and causing no clinical signs, while the animal is infecting other horses. Kentucky's protocol involves culturing at-risk stallions (in this case, those that were on the index farm with the affected horse). Stallions that return negative cultures are then bred to two different test mares (who themselves are proven free of the organism through no less than three separate cultures prior to the test breeding). Following breeding, the test mares must be cultured at specified intervals. Ford stated that after a mare is covered, it will take a minimum of 35 days before officials can definitively state the stallion did not transmit the disease-causing organism to the mare. Ford said Kentucky is in the middle of culturing the mares to be used in the test breedings, which they anticipate will start in early January.

As for the affected horse, he's currently in treatment to eliminate T. equigenitalis from his system. Since the bacterium can hide in every nook and cranny of a stallion's genitalia, this involves both external and systemic treatment.

An outbreak of CEM in 1978 among Kentucky's Thoroughbred population shut down the breeding season. The cost to the industry was estimated at $1 million a day.

The potential effects go well beyond the breeding shed and the pocketbook. As a reportable disease, the CEM case could encumber, or even potentially halt, interstate and international transport of horses.

"We don't know what the reaction will be--I'm sure there will be some," said Stout. "It will be reported to OIE (Office International des Epizooties, or World Organization for Animal Health), and each country will probably react in its own way. We do know now that some shipments have been contained and others have been allowed to move."

According to Ford, a shipment of horses destined for Brazil had to remain grounded on Sunday--Brazil and Argentina both have regulations specifying that horses coming into the country had to originate from a country "free of contagious equine metritis." Ford said that USDA officials were in talks to change these requirements to specify horses from CEM-free premises so that exportation could resume. While not yet official, it is thought that Argentina is going to allow the premises rule.

The Kentucky Department of Agriculture has been in communication with other state veterinarians. At this time, no states have placed restrictions on Kentucky horses.

Ford said that since the primary route of transmission of the organism is venereal, and there's been limited opportunity for transmission as these stallions did not perform live covers, he does not expect to see major restrictions as a result of the case.

"Our opinion is that at this time--based on the epidmemiological information gathered thus far, we don’t recognize a need that would require other states or our trading partners to impose significant movement restrictions," Ford said. "This is supported by the fact that we have an identified population of horses we consider to be ‘at risk’ of having the opportunity of exposure, we have quarantined those animals, and are currently conducting diagnostic test to better define their individual disease status.

"And perhaps of as much importance in the decision-making process of these other entities is the fact that we have historically managed disease incidences effectively here in Kentucky, to protect not only our populations in Kentucky, but throughout the world. We will not risk jeopardizing those other populations, if there is a need--we, as we have in this incidence--identify and control the animals at risk of transmitting the disease until such time as we are satisfied the risk has been eliminated."

"The nation's industries as a whole have expressed concern over this, because this is an organism that is not known to exist in this country, and our objective is to find, or determine as best we can, how this animal became infected."
--Rusty Ford

Kentucky's Commissioner of Agriculture, Richie Farmer, and Gov. Steve Beshear have discussed the issue and its potential ramifications for the state's signature industry. According to Ford, "Both have expressed confidence in our abilities and have committed that we'll make every effort needed to minimize the impact this will have on Kentucky's and the state's industries."

As testing begins and authorities work to iron out regulation wrinkles, one major question remains: where did this come from? Other than two isolated Lipizzaner stallions in Wisconsin in October 2006, the United States hasn't reported CEM since 1997.

To investigators' knowledge thus far, the affected horse was not imported, nor were any of the other horses on the farm.

"The nation's industries as a whole have expressed concern over this, because this is an organism that is not known to exist in this country, and our objective is to find, or determine as best we can, how this animal became infected," Ford said.

Keep an eye on for updates as this situation continues to develop.

  • The Kentucky Department of Agriculture also offers information on their control measures on the State Veterinarian's site,
  • Information from the USDA can be located at  
  • The chapter on CEM from the OIE Terrestrial Manual 2008 can be downloaded as a PDF file from

About the Author

Erin Ryder

Erin Ryder is a former news editor of The Horse: Your Guide To Equine Health Care. She owns a portly gray gelding named Duncan and dabbles in several equestrian disciplines, with an emphasis on dressage.

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