Get Vaccinating Right

Merck Animal Health Vaccines

Get Vaccinating Right

Illness can take an enormous toll on your horse's well-being and performance and may jeopardize its life. Properly administered vaccines represent the most economical tools available to help prevent infectious diseases.

Diseases of Concern

The diseases to which horses are vulnerable vary widely. Some are obvious, others pose hidden threats. Some target younger horses while others affect all ages. The key to good health for your horse is in knowing when, how and where these enemies might strike—and how to best defeat them. The following recommendations are for adult horses. Check with your veterinarian on proper vaccination for foals, breeding animals and previously unvaccinated horses.

Core Vaccinations

Some disease threats are significant enough to justify vaccination for every horse, every year. These are the foundation of 'core' vaccination guidelines, as recommended by the American Association of Equine Practitioners (AAEP)1. Core vaccines have clearly demonstrated efficacy and safety, with a high-enough level of patient benefit—and low-enough level of risk—to justify their use in all horses.

These are vaccines against diseases that:
  • Are endemic to a region
  • Are virulent/highly contagious
  • Pose a risk of severe disease
  • Have potential public health significance and/or are required by law

Common signs of these diseases in the horse can vary based on disease, but most have a neurological component, which can be particularly devastating to the horse.

  • Eastern/Western Equine Encephalomyelitis (EEE/WEE)
  • Tetanus
  • Rabies
  • West Nile Virus

Risk Based Vaccines

According to AAEP guidelines, risk-based vaccines are administered according to your horse's specific needs and should be directed by your veterinarian. Criteria can include your horse's age, exposure level and geography. Use of these vaccines may vary among individuals, populations and/or geographic regions. If your horse is actively training, competing or traveling—even recreationally or occasionally—you need to talk to your veterinarian about risked-based disease protection.

  • Equine Influenza (EIV)
  • Equine Herpesvirus (EHV or Rhino)
  • Equine Herpesvirus Myeloencephalopathy (EHM)
  • Strangles
  • Potomac Horse Fever (PHF)
  • Equine Viral Arteritis (EVA)
  • Rotavirus
  • Anthrax
  • Botulism

What is Havlogen®?

Havlogen is Merck Animal Health's exclusive adjuvant:
  • Produces a booster effect stimulating high, long-lasting levels of protection through the slow release and gradual absorption of antigen
  • Allows concentration of antigen (a substance to which an immune response is mounted) while minimizing adverse reactions
  • Stays in suspension and doesn't settle to the bottom of vial for consistency and potency in each dose

Antigen Purification System (APS)

A vaccine must be safe. Merck Animal Health's Antigen Purification System (APS) works to remove unwanted protein and cellular debris from the vaccine antigen. By purifying the vaccines in this method, we reduce the debris that can cause undesirable injection-site reactions in the horse.

By combining our proprietary Antigen Purification System (APS) and exclusive Havlogen® adjuvant, we are able to produce a line of killed vaccines that are highly efficacious and have an exceptional safety profile shown to be 98% reaction free in field safety trials.6

What to Expect After Your Horse is Vaccinated

While the benefits of vaccination far outweigh the risks, it is important to have realistic expectations when vaccinating your horse. After your horse is vaccinated, monitor your horse closely for 1-2 hours and allow your horse free exercise if possible.

The goal of administering a vaccine is to stimulate an immune response to help protect the horse from disease. This response creates a cascade of events within the immune system to ward off disease. As a result, some horses may experience mild and transient side effects shortly after vaccination, including:

  • Low-grade fever (less than 102°F)
  • Decreased appetite
  • Fatigue or lethargy
  • Mild heat or swelling at the injection site
  • Injection-site tenderness

These signs usually appear within 24 hours after vaccination and typically resolve within 24 to 48 hours.

More severe systemic reactions are very rare and can include sweating, elevated heart rate, respiratory distress, colic or development of hives. Call your veterinarian immediately if you see any of these signs.

Adverse reactions are not always predictable and are inherent risks of vaccination. Therefore, it is recommended that horses not be vaccinated in the two weeks prior to shows, performance events, sales or domestic shipment. Some veterinarians may elect not to vaccinate horses within three weeks of international shipment.

It is best to have your veterinarian administer vaccinations. He or she will be most familiar with your horse's medical history, and well versed in proper vaccine handling and administration techniques and will be prepared to handle more severe reactions.

Vaccination + Biosecurity is Best!

Vaccinations are only one part of a good infectious disease control program. Proper management and biosecurity practices along with vaccination can lower the incidence and severity of infectious diseases.

  • Proper Management Practices
    • Reduce exposure to pathogens (e.g., keep buckets & equipment scrubbed clean)
    • Avoid contact with non-resident and sick horses
    • Isolate all new entries or horses returning to the stable from travel
    • Isolate any horse with elevated temperature or occurrence of unprovoked coughing
    • Check temperatures at least once daily (normal = 99°F - 101°F)
    • Avoid using community water tanks
    • Wash hands after touching other horses (hand sanitizers in absence of soap and water)
    • Spray/disinfect stalls at shows
    • Reduce stress factors (e.g., avoid long distance hauling)
    • Keep in well-ventilated stalls and haul in well-ventilated trailers
    • Follow a good nutritional feeding program
  • Infectious Disease Control
    • Enhance resistance to infectious disease by vaccination
    • Reduce exposure to infectious agents in the horse's environment:
      • High population density situations like breeding farms, sales or boarding facilities and race tracks are often ideal places for transmission of infectious disease
    • Examples of factors that can contribute to increased risk of infectious disease include:
      • Stress
      • Over-crowding
      • Parasitism
      • Poor nutrition
      • Inadequate sanitation
      • Inadequate ventilation
      • Contaminated water
      • Inadequate rodent, bird and insect control
      • Movement of people, horses, vehicles and/or equipment on and off facilities during infectious disease outbreaks
  • Vaccination Efficacy
    • Vaccines alone are not sufficient for the prevention of infectious disease
    • Vaccines serve to minimize the risk of infection but cannot prevent disease in all circumstances
    • Vaccinating your horse at the right time, well before exposure to viral and bacterial diseases, is extremely important
    • Protection is not immediate after administration
    • Although rare, there is potential for adverse reactions despite proper handling and administration of vaccines
  • Storage and Handling
    • Proper storage and handling is critical to vaccine efficacy and safety
    • Keep vaccines refrigerated and out of sunlight
    • Follow manufacturers' instructions


1. AAEP Core Vaccination Guidelines 2. Wilson JH, Davis A, Bender JB, Minicucci, LA. Residual Effects of West Nile Viral Encephalomyelitis in Horses. In: 49th Annual Convention of the American Association of Equine Practitioners, 2003, New Orleans, Louisiana, (Ed.) 3. Merck Animal Health and University of California, Davis (Nicola Pusterla, DVM). Infectious Upper Respiratory Disease Surveillance Program. Ongoing research 2008-present. 4. Equine Herpesvirus-1 Consensus Statement. J Vet Intern Med 2009; 23:450-461. 5. Merck Animal Health and University of California, Davis (Nicola Pusterla, DVM). Infectious Upper Respiratory Disease Surveillance Program. Ongoing research 2008-present. 6. Data on file. Merck Animal Health.