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