On May 23, 2024, the National Veterinary Services Laboratories in Iowa confirmed a case of contagious equine metritis (CEM) in an 11-year-old domestic pony mare in Florida.
CEM is a foreign animal disease that can affect fertility in horses and ponies. It is transmitted during live cover and artificial insemination, and it can also be transmitted through contaminated equipment and human hands.
The U.S. eradicated the diseases in the contiguous 50 states in 2010. The last reported case in an American equine was in a Thoroughbred mare in Puerto Rico in 2013. The country had been considered CEM-free by the global veterinary community since then.
Factual Summary
This outbreak involves stallions, mares, and geldings; of all ages and breeds; on one farm in Central Florida.
The 11-year-old mare had been bred by live cover on May 10th to a 3-year-old pony stallion. That pony stallion has since tested positive as well, along with a second pony stallion, 8 pony mares, and one gelding.
The two stallions had been collected using shared semen collection equipment one day apart. The infected gelding was the turn-out companion for the index pony stallion. USDA says the gelding was likely exposed through routine sheath cleaning practices. Seven more pony geldings have subsequently tested positive.
The farm in question is home to 97 equines — 35 ponies (4 stallions, 18 geldings, 13 mares), 40 riding horses of various breeds (all geldings), and 22 draft horses (all geldings). USDA says that “given the significant involvement of sheath cleaning practices as a method of spread on the index farm, the 40 riding horses and 22 draft horses, which are all geldings, are being scheduled for testing.”
The first pony stallion that tested positive was bred in Polk County, Missouri, where he lived until August 2023. His dam has completed testing with all negative results.
The second pony stallion that tested positivve was born into an “essentially feral herd of about a dozen domestic ponies and donkeys” in Gallatin County, Kentucky. That herd was dispersed in 2022.
According to USDA, the isolates from this outbreak do not match the isolates from any previous U.S. outbreak.
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Impact on Maryland
This outbreak matters because Maryland has an economic interest in protecting its sport pony herd and preventing the spread of CEM to other sport horse breeds.
Maryland is home to several nationally renowned pony breeders, including Copper Beech Farm, Land’s End Farm, Loafers Lodge, Rosehaven, Slackwater, and Severn Oaks, among many others. Infected equines, including foals, can be asymptomatic and as well as long-term carriers.
In addition, sport ponies travel up and down the East Coast for competition, including important pony shows here in Maryland. Since the disease was detected in May, Maryland has hosted at least the following:
- Bel Air Welsh Classic (June 13-14)
- Penn-Marydel Welsh Eastern Regional Show (June 15-16)
- Maryland Pony Breeders Midsummer Madness (July 4-5)
- Maryland Pony Breeders Annual Show & Yearling Futurity (July 6-7)
- Maryland Pony Breeders Shetland Show (July 7)
Notable upcoming pony breeding and pony hunter shows in Maryland include:
- Open Welsh Pony Show at the Maryland State Fair (Aug. 29-30)
- Open Shetland Pony Show at the Maryland State Fair (Sept. 2)
- Maryland Horse and Pony Show (Sept. 11-15)
- Washington International Regional & USHJA Zone 3 Finals (Oct. 17-20)
- Washington International Horse Show (Oct. 17-20)
It bears noting that pony breeders often cross their pony stallions and pony mares with horses, including Thoroughbreds, Arabians, and Quarter Horses bred in Maryland. Were CEM to be diagnosed in pony breeding stock in Maryland, it could spread to other sport horse breeds.
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How to Diagnose
According to USDA, diagnosis requires either a Polymerase Chain Reaction (PCR) test or a bacterial culture test. Bacterial cultures require that a veterinarian collect swabs from the genital tract and send them to an approved laboratory for culture. The samples need special handling and must be processed within 48 hours of collection, and it then takes 7 days to get a result.
The only laboratory approved by USDA for CEM testing in Maryland is MDA’s Animal Health Diagnostic Laboratory in Frederick. The Maryland Department of Agriculture requires that veterinarians make prior arrangements with the laboratory for any requested CEM cultures.
How to Treat
Also per USDA, treatment must be performed in quarantine under the supervision of regulatory animal health officials. USDA explains that “personnel thoroughly wash the external genitalia in stallions and mares using a disinfectant soap (for example, 2% Chlorhexidine). After thoroughly rinsing the area, they apply a topical antibiotic (for example, nitrofurazone or silver sulfadiazine). Steps need to be repeated for 5 consecutive days. Most horses respond very well to one 5-day treatment; however, some may need to be retreated.”
How to Prevent
USDA has imposed import restrictions on horses coming from countries that have reported cases of CEM.
Horses imported from the Europe Union, Ireland, the United Kingdom, Norway, and Switzerland, among others, must be quarantined for at least 3 days and can only enter the country after testing negative.
The restrictions apply to horses imported permanently, as well as horses coming to the country temporarily for purposes of competition or exhibition.
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For equines already in the U.S., USDA recommends:
- Testing stallions annually before each breeding season.
- Disinfecting sheath cleaning equipment and semen collection equipment after each use.
- Maintaining breeding records for contact traceability and to help limit disease spread.
- Isolating mares showing signs of CEM and calling your veterinarian.
The Bottom Line:
Breed Responsibly
1. Quarantine new stock
2. Test stock annually
3. Practice biosecurity
4. Consult your vet