Equine Vaccination – prevention is certainly better than cure

Equine vaccinations from Torch Equine Vets

Prevention is certainly better than cure and by ensuring your horse receives its annual equine vaccinations and heathchecks you will be able to discuss any health issues with the vet, allowing early intervention should there be a problem. Protecting your horse from parasites and maintaining a healthy diet under expert advice will go a long way in ensuring that your horse stays well.

Why vaccinate?

Just as with human disease, equine vaccination helps horses fight infection and if a horse does develop disease, it will decrease the severity of signs. Immunisation is most effective when a high percentage of the horse population is vaccinated (known as herd immunity).

What does equine vaccination do?

When horses are infected naturally, defence proteins called antibodies are produced and, together with a type of white blood cell called a killer cell, they will help the horse fight disease. Both antibodies and killer cells are specific for a particular infectious organism and can continue to circulate within the immune system for a time after the horse has recovered from the disease. This will help protect the horse from getting the disease again. However, the limitation with this natural immunity is that this response can take days, by which time the disease can cause significant harm and spread to other horses. Over time, the response weakens further unless the horse is re-exposed.

Vaccines stimulate an immune response in horses by tricking their bodies into believing that they are being attacked by a disease and creating antibodies and killer cells to fight infection. This means that when natural infection does occur, the immune system is able to produce a much faster and stronger response. It is this strong response, as a result of vaccination, that prevents the disease becoming debilitating and spreading to others.

Equine vaccination contain antigens (the proteins on the surface of the organism) that are altered slightly but are still recognisable to the horse’s immune system. Therefore when a horse is vaccinated the immune system is primed and able to fight the disease it is immunised against, but not suffer the ill effects of the disease itself.

Prevention methods

It is advisable to immunise all horses. Good yard management is also important and the following tips will help keep respiratory diseases at bay.

  • Follow good hygiene procedures
    Comprehensive hygiene procedures will reduce the chances of outbreaks. Use dedicated stable equipment for each horse to help avoid infections, for example individual buckets, brushes, tack etc.

  • Quarantine
    If a horse on your yard is diagnosed with a respiratory disease, it must be quarantined immediately to prevent spread. All new horses on a yard should also be quarantined on arrival for at least three weeks and monitored for signs of disease.

  • Limit the number of horses on a yard
    Overcrowding increases the likelihood of infection spreading and should be avoided.

  • Be vigilant for signs
    Horses infected with respiratory diseases may exhibit a number of similar signs. Monitoring your horse closely will help your vet make an accurate diagnosis and reduce the chance of infection spreading. Monitoring for a rise in rectal temperature is a good way of picking up early cases of respiratory disease.

  • Be aware of horses at risk
    Respiratory diseases can affect all ages and types but those most at risk are horses kept in large numbers and those which travel a lot, for example to shows, riding club events and competitions.

  • Segregate youngsters
    Diseases such as ’flu’ are most common in youngsters under two years of age.

  • Ventilation
    Ensuring stables are well ventilated will improve respiratory health and help reduce the spread of disease.

  • Vaccination
    Vaccination is the best way to prevent your horse from contracting respiratory diseases that are caused by viruses or bacteria. Allowing your horse’s booster vaccinations to lapse may increase the risk of disease.

Equine Influenza

Widespread throughout the horse population, influenza spreads rapidly, due to a combination of a short incubation period of one to three days and coughing during early stages of the disease. The virus is transmitted by direct horse-to-horse contact and indirect contact via humans, tack, feed and equipment.

Signs include:

  • Dry, harsh cough

  • Raised temperature

  • Watery nasal discharge

  • Lack of appetite

  • Lethargy

  • Muscle soreness

  • Painful glands under the jaw

Following a bout of ‘flu’, it is important to give a horse complete rest for at least six weeks, to allow it to recover. Without rest, there is a small but increased risk of myocarditis, an inflammation of the heart muscle, which can subsequently cause an irregular heartbeat. Other complications include post-viral cough, secondary bacterial infection, bronchitis or bacterial pneumonia.

Herpes (EHV)

There are many types of herpes virus in horses with EHV-1 and 4 causing the most serious problems.

EHV is widespread in the horse population with most horses carrying the virus but not showing clinical signs of the disease. This is because the virus remains latent (hidden) within the horse, a similar phenomenon in humans where the virus periodically re- emerges to cause ‘cold sores’. The reactivation of the virus comes without warning but is often associated with stress such as transportation or weaning.

Once reactivated the virus causes disease in the horse and rapidly spreads from one horse to another.

Clinical Syndromes:

  • Neurological signs- hind limb weakness and incoordination leading to recumbancy and paralysis

  • Respiratory Disease- rise in temperature, coughing and nasal discharge

  • Abortion and death of newborn foals

EHV-1 is responsible for any of the above clinical syndromes whereas EHV-4 tends to just cause respiratory disease.

Equine vaccinations from Torch Equine Vets


Whilst the incubation period of strangles is approximately two weeks, infected horses can release the bacterium for long periods, so new outbreaks can occur weeks after the initial outbreak. About 10% of recovered horses can carry the disease after an infection of strangles and can spread the disease to other horses even though they appear healthy.

Strangles is transmitted by direct and indirect contact and particularly through shared water sources, where the bacterium lives for longer periods. It can affect all ages and types but those most at risk are youngsters, those that mix in large numbers and horses that travel a lot to competitions and riding club events.

Signs include:

  • High temperature

  • Nasal discharge

  • Cough

  • Depression

  • Lack of appetite

  • Respiratory distress

  • Enlarged lymph nodes in the throat region which can develop into abscesses

Serious associated complications include ‘bastard’ strangles (when abscesses form in other body organs) which develops in a small percentage of cases and is usually fatal. Another fatal complication is purpura haemorraghica which causes damage to blood vessels.

Not all horses will show all these signs, some may just develop a temperature and seem off-colour. As a result, the disease can remain undiagnosed until another infected horse shows more typical signs.

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Although most animals can be affected, horses are particularly susceptible. The bacteria enter the body through wounds, with punctures of the sole of the foot a common route of infection. The bacteria then cause disease by producing toxins that affect the nervous system.

Equine vaccinations from Torch Equine Vets

Signs include:

  • Muscle stiffness resulting in a ‘rocking- horse’ stance and ‘lock-jaw’

  • Difficulty moving and eating

  • Protrusion of the third eyelid

  • Seizures

Equine vaccinations from Torch Equine Vets

Ideally, all horses should be vaccinated against Tetanus, in many cases the disease proves fatal despite all attempts at treatment.

Rules and regulations

It is advisable to vaccinate all horses that regularly encounter large groups of unfamiliar horses, for example hunters and horses that take part in Riding Club and Pony Club activities.

Riders or trainers who compete under the International Equestrian Federation (FEI) or British Horseracing Authority (BHA) rules have to ensure their horses’ equine influenza vaccinations are up-to-date to enable them to compete. Most competitions do not permit equine vaccination within seven days of the event.

BHA rules

The BHA rules stipulate that a horse must have two primary vaccinations against ‘flu’ given no less than 21 days apart and no more than 92 days apart. In addition, where sufficient time has elapsed subsequent to the primary equine vaccination, the vaccination section of the passport must be completed to show that:

  • A horse has received a booster vaccination given no less than 150 days and no more than 215 days after the second component of the primary vaccination, and
  • A horse has received booster vaccinations at intervals of not more than a year apart or such lesser time as the Stewards of the Jockey Club may, in an emergency, decide
  • Equine vaccination has to be administered by a Veterinary Surgeon FEI rules

Horses competing in FEI competitions require a primary course, in accordance with BHA guidelines, with a first booster (third vaccination) within 7 months of the second vaccination of the primary course. Importantly booster vaccinations should then be given every six months.

This information is brought to you by:
MSD Animal Health, leading manufacturer of the Equilis range of equine vaccination: Prequenza , Prequenza TE, Equilis Te and Strep E.

Frequently Asked Questions

Vaccination is the best means of helping protect horses against potentially fatal diseases such as equine ‘flu’, tetanus, herpes, and strangles which can severely affect a horse’s health and performance.

The most common diseases to vaccinate against are equine ‘flu’ and tetanus, although it is also advisable to protect your horse against strangles and herpes. Our team can advise you on a vaccination or prevention programme and the frequency of booster vaccinations. If you are concerned about any diseases during breeding, for example herpes virus or rotavirus, you should also talk to us for information on a suitable prevention programme.

Booster vaccinations for respiratory disease are required from every three months to fifteen months, depending on the vaccine. Our team can advise you on this.

As in humans, vaccination is never a 100% guarantee since it relies on the ability of each horse to individually mount a satisfactory immune response. As a result, you should never vaccinate a horse that is unhealthy or stressed. A combination of having a complete vaccination programme and enough of the population vaccinated (herd immunity) is how viruses and bacteria are kept at bay. The gold standard is to have a whole yard vaccinated and follow good stable management and hygiene procedures. This will reduce the amount of infective organism in the horse’s environment.

Just as humans sometimes feel unwell following immunisation, horses also can appear off-colour after being vaccinated. This is not usually a cause for concern, but if you are worried you should talk to your vet.

  • Flu and Tetanus:

It is advisable to keep your pregnant mare up to date with her flu and tetanus vaccinations so that this immunity can be passed to her foal via the colostrum. Most ‘flu/tet’ vaccines are licensed to use in pregnancy. Speak to your Veterinary Surgeon about the most suitable time to booster your mare.

  • Herpes:

To reduce abortion caused by EHV-1 infection pregnant mares should be vaccinated during the 5th, 7th and 9th month of pregnancy.

  • Strangles:

It is not recommended to vaccinate against strangles during pregnancy.

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