REASONS for performing pre-breeding screening tests on your breed stock are abundant as the activity of breeding can spread many diseases. Disease can be spread via natural breeding but also via artificial breeding, e.g. from stallion to mare via semen. Some diseases which impact fertility can also be spread via contact and respiratory route, i.e. inhaling the disease; just like coronavirus in humans.

The diseases of most significance which we encourage everyone to test for are:

  • 1. Contagious equine metritis (CEM complex)
  • 2. Equine viral arteritis (EVA)
  • 3. Infectious aneamia (EIA)
  • Screening is being promoted by Horse Sport Ireland this breeding season in that they are offering a voucher of €50 to owners who have their horses tested for these diseases.

    Contagious equine metritis is an umbrella term for three bacterial infections which cause infertility and therefore inhibit your mare from going in foal. The bacteria are Taylorella equigenitalis, Pseudomonas aeruginosa and Klebsiella pneumoniae. While Taylorella equigenitalis is a rare and reportable disease, Pseudomonas and Klebsiella are much more common.

    Mares and stallions can “silently” carry the disease without showing overt signs of infection and can therefore “silently” transmit the disease to other animals, during cover for example. Mares, mating stallions and teasers, and stallions used for AI (fresh, chilled and frozen semen) can all act to pass this disease. Due to the nature of this disease complex, it is imperative to screen animals prior to breeding so as to rule out these diseases or to diagnose and treat accordingly.


    Screening of the above bacterial infections can be done via clitoral and/or uterine swabbing in mares and by swabbing four sites on the penis of stallions. Swabs are then cultured at approved laboratories to test for the presence of these bacteria. The laboratory process normally takes seven days to complete due to the slow growing nature of some of the bacteria in the CEM complex. There is a PCR test option for CEM which can take 24 and 48 hours. Both are available at the Irish Equine Centre.

    Equine viral arteritis (EVA) is a notifiable disease here in Ireland. The disease can show clinical symptoms such as fever, depression, eye infection (pink eye), skin rashes, nasal discharge. However animals can be carriers and can spread disease without overt signs of infection. This can subsequently cause abortion and infertility. Stallions exposed to the virus can become permanent carriers, can often continue to shed and can therefore infect every mare that they cover (naturally or via AI). Therefore, an infected stallion should no longer breed. The reasons for screening for such a disease are clearly abundant. At the moment no vaccine is available in Ireland for EVA and so stallion owners are correctly insisting that mares are tested for the disease within four weeks of mating.

    Equine Infectious Anaemia is a notifiable disease. We had an outbreak of this disease in 2006. Similar to EVA clinical signs vary from some animals having fever, depression, anaemia, rapid weight loss, for example, to others showing no signs at all. Disease can be spread via blood and other bodily secretions. No vaccine exists and prevention is based solely on disease screening and biosecurity.

    Fungal infections

    Finally, in some cases your veterinarian may recommend checking the mare’s uterus for common bacterial infections which may hamper your mare’s ability to go in foal. Less commonly fungal infections may result in the same outcome. Prior to breeding a swab can be taken from your mare’s uterus to check for these unwanted pathogens. Should unwanted bacterial pathogens exist in your mare’s uterus, a sensitivity test can be performed to determine what the most appropriate antibiotics might be to treat the infection.

    These steps will undoubtedly aid you in ensuring that your horses have a “clean breeding health status” walking into season 2024.