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About Equine Vaccines

With a well-planned vaccination schedule, you can help to protect your horse against a range of infectious diseases. Horse vaccines are an inexpensive, preventative measure in horse care, especially in comparison to the cost of treating a disease, and when coupled with solid animal husbandry, you can maximize the chances that your horse leads a long and happy life.

A vaccine contains a pathogen (virus, bacterium or parasite) in an altered state, and it stimulates the horse's immune system to produce antibodies to fight it. Once the antibodies are developed, the horse's immune system is better equipped to fight off the actual invading pathogen should he become exposed to it. In other words, the horse has immunity to the disease. Without immunity, a horse may become seriously ill or die as its immune system attempts to fight off the actual disease-bearing pathogen.

The period of immunity varies by disease. For example, a rabies vaccine is said to work for approximately one year, but an influenza vaccine may help fight against the "flu" for only several months because strains of flu virus are always mutating. Revaccination, or "booster shots," are required for continued protection.

While the horse's immune system responds to a vaccine, he may feel a little sore or seem lethargic. Therefore, it is always wise to give a horse several days off without stress after vaccination, and to plan immunizations at least two weeks before any stressful event such as trucking to a competition. This rest period not only helps your horse to feel better, it gives the horses's immune system the time it needs to fully develop antibodies in response to the vaccine without having to fight off other stress factors. Spacing horse vaccines out over a period of weeks can also minimize stress to the animal's immune system and optimize the chance for the best immune response.

Selecting Diseases to Vaccinate Against
Always consult with your equine veterinarian to determine which vaccines are appropriate for your horse, particularly if he has any chronic medical conditions such as Cushings Disease, insulin resistance, or laminitis, or if your horse is geriatric, a broodmare or a foal. The timing of foal vaccinations and booster shots depends in part upon whether the foal's dam received adequately-timed vaccinations and whether the foal had sufficient consumption of the mare's first milk, which passes antibodies to the foal. Your veterinarian can assess your horse's risks of developing certain diseases while weighing any potential contraindications for a vaccine with your horse's medical conditions. Then you can set up a schedule for administering the horse vaccines and subsequent booster shots, if required.

The American Association of Equine Practioners ( categorized equine diseases into two groups: Core vaccines and Risk-Based vaccines. Core vaccines are described as being endemic to a region, being highly infectious, posing serious health risks and causing severe disease. They include:

  • Tetanus
  • Rabies
  • Eastern/Western encephalomyelitis
  • West Nile Virus

Risk-Based Vaccines are considered for administration according to a horse's risk of exposure and along with a veterinarian's recommendation. They include:

  • Anthrax
  • Botulism
  • Equine herpesvirus (Rhinopneumonitis)
  • Equine viral arteritis
  • Equine influenza
  • Potomac Horse Fever
  • Rotaviral diarrhea
  • Strangles

Here is an overview of each of the core and risk-based diseases:

Tetanus - Nearly always fatal, tetanus is sometimes referred to as lockjaw. It affects the muscles and nerves in the body; rigidity of muscles in the neck and jaw may prevent eating and drinking, and legs may seem locked into a stiff stance. Tetanus is caused by bacteria that produces toxins and which is found readily in soil. The bacteria enter the body through puncture wounds or lacerations (or the umbilicus of a newborn foal). Every horse should receive a yearly tetanus vaccine as well as a booster in the presence of a deep wound.

Rabies - Always fatal, rabies is transmitted to horses through the saliva (usually through a bite) of an infected animal. Rabies attacks the horse's central nervous system and leads to brain dysfunction and drastic changes in behavior, including aggression. Rabies has been found in raccoons, skunks, fox, mice and other animals, and it can be transmitted between species of animals, including from horses to humans. Every horse should receive a yearly rabies vaccine as well as a booster in the event of a bite from an animal that is confirmed to be rabid.

Eastern/Western Encephalomyelitis - Commonly referred to as sleeping sickness, encephalomyelitis is a degenerative disease of the brain. Several strains exist: Eastern, which is fatal, Western which is sometimes fatal, and Venezualan, which is usually fatal. All are spread through the bites of blood-sucking insects, such as mosquitoes, who acquire the virus while feeding on birds and rodents. Risk of exposure varies slightly according to weather conditions and geographic location, but the severity of the disease suggests that every horse should be vaccinated yearly. The vaccine is often combined with tetanus vaccine, and should be administered before mosquitoes emerge.

West Nile Virus - West Nile Virus is spread through the bite of mosquitoes that contract it while feeding on infected birds and animals. It attacks the horse's central nervous system and brain. Some horses die from the disease, while others can survive the acute illness with veterinary care. Survivors may have residual effects of the disease. Horses should be vaccinated yearly against the disease before mosquitoes emerge.

Anthrax - Caused by Bacillus anthracis, anthrax is a serious and fatal disease. The bacteria survive only in alkaline soil in limited geographical areas. Spores of the bacteria enter the horse's body by being inhaled, ingested or through a wound.

Botulism - Botulism is a serious and often fatal disease caused by various potent toxins that are produced by Clostridium botulinum. The bacteria survive in soil and produce spores which can be ingested or can enter the horse's body through a wound. The botulism toxins block the transmission of impulses to nerves in the body, resulting in paralysis.

Equine Herpesvirus (EHV) - Also referred to as Rhinopneumonitis or "Rhino," this disease is caused by two different viruses EHV-1 and EHV-4. Both affect the respiratory tract. EHV-1 can cause broodmares to abort, deliver a non-viable foal and death. "Rhino" is very contagious as it spreads through the air and through either direct or indirect contact with nasal secretions; contaminated farm utensils and drinking water or other receptacles can spread the disease. Rhino is particularly hard on young horses, and while it isn't necessarily always fatal in an otherwise healthy horse, treatment is expensive and downtime is lengthy.

Equine Arterial Arteritis (EVA) - Caused by the equine arteritis virus, EVA is contagious but typically not life-threatening to otherwise healthy horses. Symptoms of infection are varied and are easily missed. EVA is spread through virus-laden respiratory secretions and venereal secretions. The virus can cause abortions in broodmares, pneumonia and death to foals, and cause breeding stallions to become carriers.

Equine Influenza - Influenza is caused by a virus that affects either the lower or upper respiratory tracts of the horse. "Flu" symptoms are similar to those seen in humans, including loss of appetite, cough, nasal discharge and fever. It is highly contagious and spreads easily through the air. Consider vaccinating your horse if he or she travels or is part of an open herd; subsequent boosters within the year may be warranted depending on your horse's exposure.

Potomac Horse Fever - Potomac Horse Fever received its name when it was originally identified in horses living in Maryland near the Potomac River, though it is now known to exist in other parts of the United States and Canada. Potomac Horse Fever occurs from late spring to early fall, and is caused by a bacteria that is hosted by fresh water snails and water insects. Horses become exposed to the disease through ingestion of feed that contains the carcasses of host insects or water containing larva of host water insects and snails. Symptoms can include depression, fever, laminitis, colic, severe diarrhea and the disease can lead to death.

Rotaviral Diarrhea - Also known as Rotavirus, this is the infectious cause of diarrhea in foals. If left untreated by a veterinarian, Rotoviral diarrhea can be fatal to a foal.

Strangles - Also known as equine distemper, strangles is a highly contagious infection caused by the bacteria Streptococcus equi. Though it is rarely fatal, Strangles requires lengthy treatment, and an infected horse can carry the bacteria for years without showing signs of the disease. Strangles causes the lymph nodes in the upper respiratory tract to swell and abscess. Streptococcus equi can be spread between horses through direct contact, and in many other ways including hose nozzles, farm utensils, pastures, grooming equipment, hands and clothing of handlers, and so on.

Tips to Supplement Your Vaccine Program

  • To help fight against mosquito-borne diseases, remove all standing water, which is the breeding ground for mosquitoes, from your property.
  • Keep horses indoors during dawn and dusk, which are the times that mosquitoes are most active.
  • Keep the lights off as much as possible at night; lights attract pathogen-carrying bugs from mayflies to mosquitoes.
  • If possible, use screens on your barn windows and doors.
  • Disinfect water and feed tubs regularly.
  • Require a veterinarian's health certificate for any horse that is new to your farm, and segregate the horse for a minimum of two weeks to observe for signs of illness.
  • At equestrian events, use your own feed and water tubs and do not allow your horse to graze in common areas.
  • Use insect repellants on your horse and yourself to protect against bug bites.
  • Prevent over-crowding, provide clean water and adequate amounts of quality food.

Related Topics:
Maintaining an Equine Medical Kit
Printable Routine Equine Medical Record
How to Use Equine Vital Sign

*Source: American Association of Equine Practioners (AAEP)