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Why SBS Requests Disease Testing of Stallions

August 07, 2016

Posted by SBS in Disease and Health Testing

Select Breeders Services (SBS) and its affiliate labs require current negative test results for specific diseases for stallions presented to our facilities for freezing which can include Contagious Equine Metritis (CEM), Equine Viral Arteritis (EVA) and Vesicular Stomatitis (VS) as well as a negative Coggins. Depending on the facility, the tests may be required prior to the stallion’s arrival or performed at the time of collection. What does all that mean and why are these negative tests necessary? In this article we will discuss the way these diseases are transmitted, how they can be prevented, why we require they be performed and provide examples of what can happen if an outbreak of these diseases occur.

When exporting equine frozen semen there are tests which need to be performed during a specific time frame according to the regulations of the importing country. What if your stallion is only being collected for frozen semen to be used within the United States or he is just visiting SBS for a semen evaluation or processing of cooled semen shipments? Why would SBS require these ‘non-export’ stallions be tested? The answer is very simple…testing is required to protect all stallions at the facility, including yours, from contracting a disease from an untested, asymptomatic carrier stallion. Having an infected stallion, or mares infected because they were bred with infected semen, could be devastating to a stallion’s breeding career, his reputation and your breeding business. Also, if an SBS facility has a positive case for these diseases it could jeopardize their ability to export qualified doses already in storage or future collections.

Contagious Equine Metritis (CEM)

As defined by the USDA, Contagious Equine Metritis (CEM) is a venereal disease of horses caused by the bacteria Taylorella equigenitalis. CEM is a reportable disease which means if there is a positive case the USDA must be notified. Countries are defined as either ‘CEM Free’ or ‘CEM Affected’. Currently, the USA is classified as being free of CEM. This disease is spread through breeding or through contact with contaminated objects, such as artificial vaginas (AV) or breeding phantoms. It is not easy to recognize if an animal is infected because stallions do not show any signs of the disease and mares can be infected without displaying any obvious symptoms. If mares do show signs of the disease it may present itself as a vaginal discharge.

Though an animal my not be visibly affected this disease can have a negative impact on the fertility of an infected mare. Abortion does not typically occur if the mare contracts the disease while she is pregnant but she may become infertile for a period of time after infection. If she is pregnant and contracts the disease she could pass it to her unborn foal.

The protocol for testing stallions for CEM requires a set of cultures with Amies Charcoal media from his urethra, urethral fossa, prepuce and semen/pre-ejaculatory fluid. The fertility of a stallion is not affected by the disease but he can harbor it on his external genitalia and spread the disease via breeding or due to unclean conditions of collection equipment. If a mare or stallion are found to be positive for CEM they are to be segregated from other animals until treatment has cleared them of the disease.

CEM was first reported on horse breeding farms in England in 1977. Then in 1978 it was found in Kentucky as the result of horses which were imported from Europe. Another outbreak occurred in Missouri in 1979. The disease was eradicated after these incidents and the United States had been considered “free” of CEM since that time. However, in 2008 a case of CEM was reported by the USDA in a 16 yr old Quarter Horse stallion who was standing at a breeding farm in Kentucky.

As a result of the CEM outbreak in 2008, it was found that at least 22 stallions and 5 mares had contracted the disease. However, nearly 1000 horses were possibly exposed to the disease as a result of shipped semen or contact with contaminated objects. Testing on each of nearly 1000 animals had to take place in order to make sure the exposed horses did not contract the disease. The USDA required extensive testing be performed. This included having stallions live cover at least two mares and subsequent negative cultures taken from the mares after mating to prove the treatment was effective. All of this was at the expense of the stallion owner/manager. Such a rigorous testing schedule would have taken stallions out of the breeding shed for weeks and resulted in a loss of income for stallion owners/manager. Please note, SBS does not require the live cover of stallions for CEM testing.

As of today, a definitive source of this outbreak has yet to be determined. The USDA is confident there was one source, believed to be an imported stallion from Europe, and not multiple sources for this particular disease outbreak. You may visit the USDA website for additional ‘Questions about CEM’ or information about the ‘CEM Outbreak in 2008.’

Equine Viral Arteritis (EVA)

Equine Viral Arteritis (EVA) is a highly contagious, infectious viral disease of horses with symptoms such as fever, nasal discharge, loss of appetite, respiratory distress, skin rash, muscle soreness, conjunctivitis and depression. It may also present itself as swollen genitals in the stallion, swollen mammary glands in the mare, swollen limbs and/or swollen eyes with a noticeable discharge. The most notable symptom for mares is abortion which can occur in as much as 70% of EVA infected mares. It is also possible for horses to have the disease but show no symptoms.

EVA can be classified primarily as a respiratory disease which spreads from the nasal discharge of an infected animal to other horses in close proximity such as in a herd, stable, etc. However, it can also be shed in semen of an acutely infected or carrier stallion. Although most horses will recover fully from the disease it is possible for a stallion to remain a carrier of the disease for the remainder of his life. This is because the virus persists in the accessory sex glands of the stallion. Even if a stallion does become a carrier of the disease he can still breed mares and they can safely carry the foal to term as long as she was vaccinated against the disease prior to being bred.

Unlike CEM, this virus can be prevented via a vaccine. Prior to vaccination it is recommended a blood sample be taken to show the horse was negative prior to being placed in isolation. After the blood is drawn the animal should remain in isolation until the vaccination is administered. It is recommended a second blood sample be drawn immediately prior to vaccination to verify the horse remained negative for EVA after entering isolation but before the vaccine was given. The vaccinated animal should remain in isolation for approximately 21 days to make sure they do not spread the virus to seronegative animals because the vaccine is a modified live vaccine.

In 2006 there was an outbreak of EVA which originated on a large Quarter Horse breeding farm in New Mexico. The disease was detected after a large number of mares sharing the same pasture were found to have lost their pregnancies at their 60-day pregnancy checks. All of the stallions on the index premises became infected and as a result became carriers and shedders of EVA through their semen. Initially, the transmission of the disease would have been due to respiratory infections on the premises but then spread by venereal means once the stallions became infected. After the investigation it was found that horses in 10 states had EVA. As a result of this outbreak many pregnancies were lost, stallions were quarantined and couldn’t breed mares during breeding season thus resulting in financial losses for several horse owners. Please visit the USDA website for ‘Additional Information about EVA’ or information about the ‘EVA Outbreak in 2006’. You can also find the recommended vaccination schedule for EVA on the AAEP website.

Vesicular Stomatitis (VS)

Vesicular Stomatitis (VS) is another disease some SBS Affiliate Labs may require prior to the arrival of a stallion at their facility or before freezing is performed in a mobile laboratory. VS is a contagious disease which affects many species including horses and humans. It is a reportable disease not only within the United States but internationally because it closely mimics foot-and mouth disease or swine vesicular disease. Vesicular Stomatitis is rarely life threatening and does not affect the fertility of mares or stallions but can cause financial losses within the horse industry both domestically and internationally. If an outbreak occurs within the US other countries could block the trade of semen, embryos or animals. Also, states within the USA, Kentucky for example, have been known to restrict the movement of horses from states with known cases of the disease.

Clinical signs of VS include blister-like lesions on the tongue, mouth, nose, lips and/or coronary bands. A blood test can confirm if the horse has VS. Infected horses can be kept comfortable with medications and feeding soft foods. Typically, VS is more prevalent in warmer climates during the summer months thus it’s believed insects such as biting flies transmit the virus. However, it can also be transmitted from horse to horse via infected buckets, equipment, etc. Please visit the USDA website for ‘Additional Information about VS’ or information about the most recent ‘VS Outbreaks’.


Each of the above diseases can have a negative impact on the health of a stallion, their reputation, breeding career, and income. However, the reach can be longer when you consider mares could lose their foals or competitors could lose their time in the show ring or on the track. SBS acts as an advocate to keep you and your horses safe while in our care. This is why we ask for these negative tests on every stallion we work with at our facilities. Testing requirements may vary with affiliate location and may change depending upon the risk status of a disease and/or current outbreaks. Visit our FAQ, What health testing do you perform on a stallion before freezing?, for additional information. Please feel free to contact your Affiliate Lab with any questions about required testing for your stallion or mare prior to arrival.

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Please Note - photos used in these news articles are available in the public domain, have been purchased through istockphoto or (when referencing breeders or horses) have been submitted to Select Breeders Services Inc. by the breeding farm or horse owner. Photo credit has been provided where applicable. If at anytime you see something that needs to be addressed please feel free to contact us directly.

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