Foal Vaccinations

Foal vaccinations are an important part of equine health. Learn what diseases foals are vaccinated against and at what age. This blog will discuss different diseases foals are vaccinated against, at what age vaccinations are started, and the importance of vaccination.

The core diseases foals are vaccinated against are tetanus, equine viral encephalomyelitis (EEE/WEE/VEE), West Nile Virus, and rabies.

• Tetanus
• Equine Viral Encephalomyelitis
• West Nile Virus
• Rabies

The common noncore (risk-based) diseases foals are vaccinated against are Equine herpesvirus (1 & 4), Influenza (respiratory diseases), Botulism (type B), Rotavirus, and Streptococcus equi subsp. equi (Strangles). There are more risk-based diseases foals are vaccinated against that are not discussed in this blog.

• Equine herpesvirus (EHV)
• Equine Influenza
• Botulism
• Rotavirus
• Streptococcus equi subsp. equi (Strangles)

Maternal-derived antibodies (MDA) are an important factor that determines the age a foal is vaccinated. Other factors include the disease the foal is being vaccinated against, safety studies and labeling of the vaccine, the level of risk for infection of a particular disease, and geographical location.

General guidelines:

Vaccinate foals at approximately 4-6 months of age against core diseases who are born to a vaccinated mare during the prepartum period. Vaccinate foals at approximately 3-4 months of age who are born to an unvaccinated mare during the prepartum period. Administer the tetanus toxoid vaccine as early as 1 month of age if the foal is born to an unvaccinated mare.

Vaccinate foals against equine herpes virus starting at 4-6 months of age and influenza virus starting at 6-7 months of age.

Vaccines are important because they minimize the risk of disease and are part of an animal management program to promote health, productivity, and performance in horses.

Vaccines alone, in the absence of proper sanitization management practices and biosecurity directed at infectious disease prevention and control, is not sufficient to prevent infectious disease transmission.

Foal Vaccination Chart – aaep.org/resource/foal-vaccination-chart/

Foal Vaccination Chart PDS

AAEP Foal Vaccination Guidelines

Tetanus is a neuromuscular disease caused by exotoxins produced by the bacteria Clostridium tetani. The disease is characterized by muscle rigidity and spasms and has a high mortality rate. C. tetani bacteria are ubiquitous in the soil and found in the gastrointestinal tract and feces of horses and other animals. Horses generally acquire the disease via wounds, surgical incisions, exposed tissue such as the umbilicus of foals, and injury to the reproductive tract in mares.

Equine viral encephalomyelitis is a neurological (principally forebrain dysfunction) disease caused by a virus that is transmitted by a vector (the mosquito). Some clinical signs include fever, obtundation, lethargy, abnormal mentation, peculiar looseness of the lips, and ataxia. In the early phase of the disease, owners can confuse it with colic. The mortality rate is high for this disease, with EEE having the highest mortality rate. Younger horses are more susceptible.

There is a geographical distribution difference of the viruses. EEE has historically occurred in the eastern, southeastern, and southern states of North America (NA). WEE has historically occurred in the western and midwestern states of NA. VEE is a reportable foreign animal disease in NA but is endemic in South and Central America. In the past (decades ago), there have been cases in Mexico where the outbreak crossed the US border. Currently, it is not recommended to vaccinate horses against VEE in most of the US; however, certain states might have a different protocol based on the risk of exposure.

West Nile Virus is a neurologic disease caused by a virus that is transmitted by mosquitoes. The virus life cycle is propagated through birds and mosquitoes. Horses with the disease might show muzzle twitching, ataxia, abnormal mentation and behavior, and recumbency. There are other clinical signs not mentioned. Mortality rates were reported to be approximately 44%.

Rabies is an infrequent neurologic disease caused by a virus that is transmitted via saliva from a bite of a rabid animal, mostly wildlife (raccoons, foxes, skunks, and bats). A rapid progressive encephalitis characterizes the disease. Although rabies incidents are low, the disease is fatal and has major public health significance. It is recommended that all horses at risk of exposure to wildlife, should be vaccinated.

Equine herpesvirus causes respiratory disease in foals. The two strains included in the vaccines are EHV-1 & 4. Clinical signs include fever, lethargy, nasal discharge, lack of appetite, and cough. EHV-1 can also cause reproductive disease (abortions) in mares, neurologic disease (Equine Herpes Myeloencephalopathy, EHM), and chorioretinopathy.  Most foals become infected with EHV-1 and EHV-4 within the first year of life. Clinical signs vary in severity from subclinical to severe. Horses recover but remain latently infected. Practicing good biosecurity and hygiene are important parts of preventing the spread of disease rather than solely relying on vaccination.

Equine influenza is a highly contagious viral respiratory disease. The virus is spread between horses by direct contact (e.g., aerosolized airway secretions) and indirect contact (e.g., fomites). Clinical signs include nasal discharge, coughing, fever, lethargy, and anorexia. There is a high morbidity rate with this disease, and most horses recover. Higher-risk populations include race horses, show horses, horses in training or boarding facilities, and horses at breeding farms.

Botulism is a neuromuscular paralytic disease caused by a neurotoxin produced by the bacteria Clostridium botulinum. The vaccine is a toxoid vaccine against C. botulinum type B, which causes toxicoinfectious botulism in foals. Another name for the disease is Shaker Foal Syndrome. The disease results from toxins produced by vegetation of ingested spores in the intestinal tract. Toxicoinfectious botulism is most common in foals 2 weeks to 8 months of age that reside in Kentucky and the Mid-Atlantic states. Clinical signs include weakness, progressing to paralysis, and frequent death. Vaccination against botulism is more common in the endemic states. Immunity against botulism is initiated with vaccination of the mare during pregnancy to induce maternal-derived antibodies that will be transferred to the foal via colostrum. Subsequent primary immunization can be administered to the foal at 2-3 months of age.

Equine rotavirus is a viral infection transmitted via the fecal-oral route and is a common cause of infectious diarrhea in foals under 60 days of age. Most clinical infections occur in foals 5-35 days of age.  Diarrhea is the most common clinical sign but varies in severity depending on several factors, a major one being the degree of hindgut maturation. Vaccination is considered where rotavirus is an endemic problem on farms. The mare is vaccinated during pregnancy to develop antibodies in the colostrum that can be transferred as passive immunity to the foal. Prevention involves good hygiene, biosecurity, and reduction in crowding.

Strangles is an upper respiratory disease in horses caused by the bacteria Streptococcus equi subsp. equi. Strangles also has the potential to infect the lower respiratory tract and other organs. The bacteria are spread between horses via direct contact with infected horses or subclinical carriers and by indirect contact with fomites. Fever is the first clinical sign before bacterial shedding. Additional clinical signs are lethargy, anorexia, lymphadenopathy, lymph node abscessation, purulent nasal discharge, and guttural pouch empyema. Strangles is highly contagious and can occur in any age group of horses, although weanlings and yearlings are primarily affected. Vaccination is not routinely recommended for horses kept in low-risk situations but is considered for horses at high risk or at farms where Strangles is a persistent endemic problem.

Usually at 4-6 months of age and the first booster starts 3-4 weeks later.

Tetanus antitoxin and tetanus toxoid are two different things. The mare should be vaccinated with a tetanus toxoid 4-6 weeks prepartum, which will give the foal passive immunity through the mare’s colostrum. The foal will require a tetanus toxoid vaccine at 4-6 months of age. If the foal is born to an unvaccinated mare during the prepartum period, then vaccinate with tetanus toxoid at 1 month of age. Tetanus antitoxin should not be given to a foal unless it sustains a wound or has tetanus disease. Tetanus antitoxin can be associated with a life-threatening disease called Theiler’s Disease aka serum sickness.

About Me