Shaping the future of animal health

Immune Boosters for Horses

Equine Repiratory Disease Complex (ERDC) - What is it?

Respiratory disease in Australia is most commonly caused by Equine Herpes Virus (EVH-1 and EVH-4). These viruses cause an upper respiratory tract infection in susceptible horses, causing disease that is very similar to a head cold or the flu in people.

Horses usually inhale viral particles via aerosol droplet transmission (ie they breathe in sneezed droplets from another infected horse). They can also become infected through contact with contaminated dust or feed. Once infected, the virus has an incubation period of 3-4 days. Infected horses usually carry the virus for around 7 days, though it can persist in nasal secretions for up to 20 days.

Common Causes of ERDC

Common causes of ERDC include:

  • Equine herpesvirus (rhinopneumonitis)
  • Equine influenza virus
  • Equine arteritis virus
  • Equine adenovirus
  • Common secondary bacterial infections such as:
    • Streptococcus zooepidemicus
    • Streptococcus equi (strangles) 
    • Rhodococcus equi (rattles)

Clinical Signs of ERDC

While several viruses have been identified as causes of equine respiratory disease complex, the clinical signs and consequences are similar:

  • cough
  • fever
  • nasal discharge
  • enlarged lymph nodes
  • loss of appetite
  • lethargy
  • slow recovery from exertion
  • missed training

Even before clinical signs of ERDC fully appear, the effects of reduced respiratory function may be apparent in a horse’s performance. Therefore, it is imperative to promptly treat a horse at the first indication of respiratory compromise. 

Competition horses are placed at increased risk for ERDC due to frequent, lengthy transportation, busy show environments, exposure to large numbers of other horses, and other stressful situations. Immune stimulants may be used to help prevent the risk of developing ERDC in performance horses.

If neglected, ERDC can escalate into secondary bacterial lung infections that may result in chronic problems and permanent damage to the horse’s respiratory tract.

How does an immune stimulant differ from a vaccine?

Unlike antibiotics and vaccines, which target specific bacteria or viruses, an immune stimulant activates a non-specific immune response to target many agents that a horse’s immune system may recognise as a threat. Because of this rapid and general response, immunotherapy is a valuable addition to standard treatments for both bacterial and viral ERDC organisms.

The use of an immune stimulant, either prophylactically or before an infection becomes fully established, can reduce the severity of clinical illness, the likelihood of tissue damage (e.g. lungs), and the spread of disease, which ultimately shortens the horse’s recovery time.

What are the benefits of immune stimulation?

Consistent performance
Microbial resistance can be a problem with antibiotics, because these drugs typically have only one mode of action. Immune stimulants help create a multi-faceted attack by the horse’s own immune system. Multiple scientific studies proving the benefits of immune stimulation have been conducted around the world.

Depending on an individual horse’s response, your veterinarian can tailor the immune therapy as required. This allows the veterinarian to customise the patient’s care by amending the dose and number of treatments.

Immune stimulation is safe to use in adult horses, ponies, and foals. Avoid immune stimulants containing an oil base as this may cause serious adverse reactions in susceptible horses.

As with any equine biological, in rare instances immune stimulants may induce a mild, transient increase in body temperature, inappetance, and lethargy.

Cost Effective
Because immune stimulants enhance the horse’s first line of defence, its immune system, and shortens the recovery period from illness, there are substantial savings from the reduction in use of expensive antibiotics, lost training time, and missed performances.

Talk to your vet

Immune stimulants are available only from your veterinarian, so please discuss the use of immunotherapy with your vet. They will be able to provide advice suitable for each horse’s individual circumstances. For product specific or technical information, please ask your vet to contact Virbac Animal Health directly.


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