Has your horse had its fall flu shot yet?

Farm Forum

Respiratory diseases are extremely common illnesses that limit performance horses, probably second only to lameness. Respiratory diseases can be viral, bacterial, immune mediated (allergies), or mechanical in nature. Some are highly contagious while others are limited to the affected individual horse. While some diseases can affect both the entire respiratory system, most are categorized as either upper airway disorders or lower airway disorders. Disorders of the upper airways are generally mechanical in nature while those of the lower airway are often the result of infection.

All horses traveling this fall and horses at training and boarding facilites need to have their fall influenza/herpes vaccine boostered from this spring. The strangles vaccine should also be given at least once per year and possibly twice depending on risk. Consult your local veterinarian for their recommendations.

Equine influenza (flu) is the most common viral respiratory disease in horses. It affects the upper and lower respiratory tract of horses and is highly infectious, with an incubation period of 1 to 3 days. After contracting the virus, horses can remain contagious for up to 10 days. Clinical signs are similar to other respiratory infections, making it difficult to distinguish equine influenza from other diseases without laboratory tests. However, if the illness spreads rapidly in a barn and certain symptoms are present, that is usually indicative.

Symptoms can include:

• Fever

• dry, hacking cough

• clear discharge from the nostrils and eyes

• loss of appetite or depression

The virus is easily spread by particles released into the air when an infected horse coughs, but it can also be transmitted by contaminated items such as brushes or clothing. Horses that are frequently exposed to new horses, such as those that travel to shows, are at greater risk of contracting the disease than are those who have never been vaccinated and those without previous exposure to the virus.

Fortunately, equine influenza is generally not a serious health hazard for adult horses, though it can be quite dangerous for foals. In most cases, horses will fully recover within 2 to 3 weeks, though complications such as secondary pneumonia can occur.

Initially it can be confusing to differentiate from allergies with the fall harvest and dust to strangles or influenza, this is where you will need the help from your local veterinarian.

Treatment for uncomplicated equine influenza generally requires little more than rest. The general rule of thumb is to rest the horse one week for every day of fever it had. NSAIDs (bute or banamine) may be given if the horse’s fever rises above 104 degrees; but since the disease is viral in nature, antibiotics are not always needed. Antibiotics are sometimes used to protect against a secondary infection which may occur when the horse’s immune system is stressed, and when they have a low white blood cell count.


Vaccines are available and recommended for the control of equine influenza. While they do not necessarily always prevent a horse from becoming infected, immunized horses tend to recover more quickly with fewer complications. Horses that are exposed to new horses frequently should be vaccinated every 6 months. Hygiene is also important for the prevention of the spread of equine influenza. Equipment and tack used on an infected horse should not be used on other horses. Handlers of sick horses should wash their hands with soap and water and change their clothes and shoes before entering areas housing uninfected horses.

Dr. Darin Peterson, DVM, was born and raised on a horse and cattle ranch in Rosholt, S.D., and received his B.S. in Animal Science from SDSU. He concentrates most of his work time with large animals. He can be reached at 701-347-5496 or