Aged Horses Show Reduced Vaccination Response

The old gray mare's immune system ain't what it used to be.

Aged horses appear to be less able to respond to vaccinations as well as their younger counterparts, said a collaborating group of veterinary researchers from Prince Edward Island, Oklahoma, and Colorado.

Immunosenescence is defined as alterations in the immune system associated with aging. Immunosenescence is important in the equine industry as it could lead to an increased susceptibility to infectious, autoimmune, and neoplastic diseases in horses.

To evaluate the effect of age on the production of antibodies in response to vaccination, the research team vaccinated 29 healthy adult horses (4-12 years) and 34 healthy aged horses (20 or more years) against rabies and influenza. They took blood samples at 0, 4, 8, and 24 weeks after vaccination to evaluate the horses' immune responses.

Horses included various breeds with a history of influenza vaccination. Since Prince Edward Island in Canada, where the study was conducted, is free of rabies, the horses had not been vaccinated against rabies previously. Thus, this rabies vaccine was used to assess the primary immune response while the influenza vaccine assessed the secondary (anamnestic) immune response.

Key findings of this study were:

  • Healthy aged horses mounted an immune response to the rabies vaccine that was similar to that of the younger horses, and
  • Aged horses had a significantly reduced response to the influenza vaccine compared to the younger horses.

According to the research team, "the clinical significance of these findings warrants further research."

Since older horses (20 or more years) comprise approximately 15% of the North American equine population and a high quality of care is demanded for these animals, further research studies in aged horses are needed.

The study, "The effect of age on the immune response of horses to vaccination," was published in volume 142 of the Journal of Comparative Pathology. The abstract is available on PubMed.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.