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Routine Vaccination of Breeding Horses

Once a decision is made to breed a mare, it’s important that we ensure that her health is managed appropriately so that not only does she successfully get in foal, she retains the foal for the duration of pregnancy and she raises a healthy foal.

Vaccination is a vital part of these equine health management programs for both mares and foals. Here we discuss the important core vaccinations for mares in Australia. Information on vaccination protocols specifically for foals are discussed in another article, Routine Vaccination of Foals.

Vaccinations For Broodmares

Due to the frequency of movement of horses between equine stud farms and owner properties, the majority of breeding facilities will require that all mares are vaccinated against Strangles, Tetanus, Equines Herpes Virus (EHV-1,4) and Salmonella. Depending on your location, vaccination against Hendra Virus may also be required.

Even if a mare is staying on your property, it is still worthwhile considering the same series of vaccinations.

Equine Herpes Virus 1

There are 5 strains of EHV that affect domestic horses, of which EHV-1 and EHV-4 can cause abortion, EHV-1 being the highly contagious strain that can result in abortion storms and/or birth of weak, nonviable foals. EHV-1 is responsible for most late gestation abortions (>7months). Mares that abort due to EHV-1 infection shed large volumes of virus into the environment via the foetus, placenta and foetal fluids. Infection can also be transmitted between horses via the reproductive tract and to a lesser extent the respiratory system.

Horses can be asymptomatic carriers of the disease, shedding the virus that may infect other horses without appearing clinically ill at the time. Some horses can also become infected, yet don’t become ill and abort until stress (often travel, unrelated illness) results in reactivation of the virus.

Even if a mare has aborted due to EHV-1, immunity is incredibly poor necessitating the need for yearly booster vaccinations. The most common protocol for EHV-1 vaccination requires boosters given at 5, 7, and 9 months of gestation. If a property or horse has had EHV-1 previously, an additional vaccination at 3 months will often be recommended.

Other horses on the property (maidens, dry mares, stallions and foals) should also be vaccinated to help prevent abortion in mares and respiratory disease in other horses.

Equine Salmonella Vaccination

Salmonella is a highly contagious disease that causes severe life-threatening diarrhoea. It can be a difficult disease to treat and in foals can also result in osteomyelitis (bone infections). Salmonella is particularly difficult to control and prevent as it is widespread in the environment and in faeces of healthy horses. Infection and outbreaks are often dependent on the virulence of the particular strain.

Transmission can occur via contamination from the environment, feed, or water or by contact with animals actively shedding the bacteria. Animals who are experiencing some sort of stress are most prone to development of salmonellosis.

The recommended program for salmonella vaccination in broodmares is:

Salmonella vaccines should not be given to breeding stallions.

Vaccination Of Stud Horses Against Hendra Virus

Hendra Virus is an important zoonotic disease of horses located in QLD and upper NSW regions of Australia. A horse can contract Hendra virus directly via sniffing or eating matter recently contaminated with flying fox urine, saliva or birth products. An infected horse can also spread infection to other horses (and humans) via body fluids and nasal secretions.

Hendra virus infection in horses is often difficult to recognise due to a wide range of clinical presenting signs that can mimic other conditions. Initial signs noticed often include a mild nasal discharge or fever and colic-like symptoms.

As the disease progresses, the horse will often have difficulty breathing and show weakness with neurological signs such as an uncoordinated gait and muscle twitching that quickly progresses to recumbency and death.

Previously unvaccinated mares and stallions require two initial vaccinations given 3 to 6 weeks apart, followed by a booster 6 months later. All horses who have received the initial three vaccine protocol then require yearly boosters.

Source: https://www.abc.net.au/news/2011-09-12/hendra-virus-explained/2881140?nw=0&r=Map

Vaccination For Tetanus and Strangles

Clinical signs and transmission of Tetanus and Strangles were discussed in our previous article, Routine Vaccination in Horses - Tetanus and Strangles. With regards to vaccination of broodmares, it is recommended that they receive a booster 4-6 weeks prior to foaling to help boost antibodies in colostrum that will provide immunity to the foal.

If you are running other horses on your property, it is important to keep them up to date with vaccinations as they can be an important source of infection in your breeding mares and foals.

Many vets will recommend that you include these other horses (usually maiden or dry mares) with wet mares for the EHVI boosters and give them an annual booster of Salmonella, Strangles and Tetanus on a date that is easy to remember, like 1st August.

About the author

Dr Leigh Davidson BVSc, BApplSc

Director at Your Vet Online

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