Introduction to Vaccines

For horse owners, vaccination is a part of the routine maintenance of the animal’s health. Vaccination can prevent disease, reduce the severity of disease, and minimize the spread of disease. With one horse, the focus is on disease prevention. With more than one horse, the focus is on reducing the impact of an outbreak.  

A horse has no specific defense when faced with a new pathogen (virus or bacteria).  Therefore, they will show the full range of symptoms of disease. To prevent this from occurring, you want your horse’s immune system to recognize and destroy the specific pathogen. Vaccination primes components of the horse’s immune system so that when the horse is exposed to the specific pathogen, it can more quickly and effectively respond to prevent or minimize clinical symptoms.  

Vaccine Types

There are three types of vaccines, all of which contain antigens. Antigens mimic the pathogen and usually contain protein chemical fragments of the pathogen of interest or the whole dead pathogen.    

• Component vaccines also contain adjuvants to help increase the immune response;   

• Killed vaccines consist of dead microorganisms (pathogens) mixed with adjuvants;   

• Modified live vaccines (MLV) contain active viral particles rendered harmless but that contain enough fragments of the original pathogen to stimulate the immune system.  

Vaccine Administration

Most vaccines are administered by intramuscular (IM) injection. Muscle contains a great blood supply so vaccine antigens can be picked up by cells in close proximity to the bloodstream.  

Vaccines must be administered away from solid structures in the muscles like ligaments, tendons, and bones. A common mistake is to give an IM vaccine too high in the neck, causing the vaccine to enter the nuchal ligament rather than the muscle. Also, if given too close to the skin, there can be an inflammatory reaction since skin and subcutaneous (beneath the skin) tissues of horses are very sensitive to most vaccines. IM injections stimulate production of antibodies in the blood that prime the immune system to prepare it for future interactions with specific pathogens.  

Intranasal (IN) vaccines may help to improve immunity against pathogens that affect the respiratory system, and are intended to provide the respiratory tract lining with protective antibodies where the pathogen enters. Examples of IN vaccines are strangles and influenza. These types of vaccines have been effective in field trials, but it is not known for how long they are effective. Therefore, these vaccines should be given at key times, or at least every six months.  

Vaccine Considerations

One method of deciding whether or not to vaccinate is by measuring the horse’s antibody titer (antibody level).  Measuring the antibody titer before deciding to vaccinate is not a good idea in practice. This leads to vaccinating less, and vaccines are generally short-lived and not effective after a few months. A titer is generally low after vaccination and this is hard to interpret. No one knows how much of a titer is protective against disease. Treatment of disease in unvaccinated animals can be prolonged and more expensive than vaccination.  Unvaccinated animals may die from diseases such as tetanus and encephalitis, which are wholly preventable.  

Do not use vaccines in sick animals for protection against the disease the animal has, or other pathogens. Proper timing is required to generate a meaningful immune response; a sick or stressed horse’s immune system can’t respond to the vaccine, nor a reaction caused by vaccination.  

Vaccination Schedules

Most horses in the United States are regularly vaccinated against tetanus,  Eastern, Western and Venezuelen Encephalomyelitis, influenza, rabies and rhinopneumonitis. Vaccines are also available to confer protection against Equine Viral  Arteritis (in the case of breeding stock), strangles, botulism, Potomac Horse Fever, and  West Nile Virus. Vaccines should be administered by a veterinarian since serious mistakes in administration and allergic reactions can occur otherwise.  A veterinarian can effectively deal with these problems if they arise.    

The following is a general timeline of when to vaccinate your pleasure and performance horses. However, consult your veterinarian for an appropriate schedule for vaccinating pregnant mares, foals and breeding stock or consult the AAEP Guideline for Vaccination of Horses.  

Also remember to keep a record of your horse’s vaccinations. These records may be needed when showing, purchasing, or selling a horse. Vaccination records demonstrate that a horse’s health has been protected. Vaccinations are an important part of horse management that should not be overlooked; the benefit definitely outweighs the cost.  

Resources

American Association of Equine Practitioners. (n.d.). Guideline for vaccination of horses. http://www.myhorsematters.com 

King, M. (2003, March). Kick-starting the immune system. The Horse, 63–66. 

PetPlace. (n.d.). Wellness and prevention – Horses. http://www.petplace.com 

The information in this document is for educational purposes only.  The recommendations contained are based on the best available knowledge at the time of publication.  Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended.  UConn Extension does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available.  The University of Connecticut, UConn Extension, College of Agriculture, Health and Natural Resources is an equal opportunity program provider and employer.