Part two: Equine biosecurity – what does it mean?

Moderator’s note: This is the second in a three part series on equine biosecurity. To read part one on general biosecurity and vaccinations, click here.  Part three will be posted Friday.

By James Little, DVM

Equine and companion animal professional services veterinarian


Prevent contact

Many equine contagious diseases are spread from animal-to-animal through direct contact or contact with aerosolized particles containing infectious disease organisms from a coughing horse. Examples here would be EHV, equine influenza and strangles. For this reason, it is important not to allow horses to have direct contact with other horses. It is best to keep them as far away from other horses as practically possible. When a horse coughs, it produces a fine mist of tiny fluid particles composed of respiratory secretions. These particles can carry various microorganisms. These micro-droplets can travel substantial distances that could vary depending on environmental conditions such as temperature, wind and humidity levels.  It is important to remember even when a horse is showing no outward signs of infectious disease, it could still be shedding potential disease-causing “bugs”.


Isolation is an expansion of the previous point of limiting contact between horses. It involves separating a horse from the rest of a population (i.e., horses on the farm). If you travel with one or more horses, that horse should be kept in isolation when it returns to the farm and not put back in with the rest of the herd immediately. It may have been exposed to infectious disease organisms during its travels, and we don’t want it to spread them to the rest of the herd. There is a period of time referred to as an incubation period between exposure and the development of disease symptoms. It is recommended to isolate these horses for at least two weeks and to take these horses’ temperature twice a day in order to identify disease as early as possible. An important point to remember is even though a horse is not showing signs of illness, it could still be a source of infection for other horses. Horses that are obviously sick, new purchases/arrivals and friends’ horses that may be staying over are just a few other examples of horses that should be isolated. Ideally when we isolate a horse we house it in a completely separate building. This isolation unit should have its own set of equipment that only is used in there and nowhere else. Only specific, assigned individuals should enter this area. These individuals should not handle other horses or go to other areas. The route taken to get to and from the isolation area should be unique and not shared with other areas of the farm. This is ideal but not always possible or practical. If it is not possible then don’t give up. Designate the end of a barn as your isolation unit and try to stall other horses as far away in the barn as possible. Quarantine would be another word that could be substituted for isolation. Either way it doesn’t mean that your horse is sick or dirty. You are simply taking appropriate precautions.

Group horses

Horses ideally should be kept in groups with their peers according to their age, sex, use, and disease status among others. These groups are a way to separate horses according to their susceptibility to disease and/or their chances of being contagious. Examples of groups would include pregnant mares, other immunocompromised horses, breeding mares that are open, resident horses that never leave the farm, horses that do leave the farm, young horses, older horses, and actual sick horses. Pregnant mares are immunocompromised to a certain degree and are susceptible to things such as abortion caused by EHV. The immune system of a geriatric horse may not be as capable in responding to infection as that of an adult horse. Younger horses typically are more susceptible to some diseases than adults who have been able to acquire some immunity with age and vaccination. In this situation, strangles comes to mind. Horses that leave the farm periodically will have the potential to bring back those germs they may have been exposed to while traveling and would be a source of infection for others. When it is not possible or practical to have designated people assigned to the care of individual groups of horses, we should plan our movement through the horse groups in a specific order. For example, start by taking care of the most susceptible group and ending with the most contagious group (e.g., any sick horses you may have). Depending on how many groups you have, a good order of contact might be pregnant mares, followed by older horses then young horses in training then quarantined horses that are not showing signs of sickness, and finally sick horses. Again, this would have to be adapted to your own situation as everybody’s farm/facility is somewhat unique.

Check back tomorrow for the last post in the series –rodent/insect control and cleaning and disinfecting.

For previous posts from Dr. Little, click here.

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