It is hardly surprising that as many as 20% or more of the equine population consists of horses older than 20. Veterinarians report that 30% of these are afflicted with Cushing’s disease (PPID or pituitary pars intermedia dysfunction), a degenerative endocrine condition that causes muscle wasting, an overly shaggy hair coat that doesn’t shed well, and/or susceptibility to the hoof disease laminitis.

As horses age, the immune system also changes and experiences an overall decline (immunosenescence) and enhanced inflammation, now termed “inflamm-aging.” Inflamm-aging describes a key characteristic of the aging process that involves a shift toward circulation of substances (pro-inflammatory cytokines) that elicit low-grade, chronic inflammation.

In PPID horses, this immune function is even more diminished than it is in normal aging horses. So researchers have asked the question: Does PPID affect horses' immune response to vaccination?

Amanda Adams, PhD, of the University of Kentucky’s Gluck Equine Research Center, examined this, and Steve Grubbs, DVM, PhD, Dipl. ACVIM, of Boehringer-Ingleheim Vetmedica, presented her results at the 2014 American Association of Equine Practitioners Convention, held Dec.6-10 in Salt Lake City, Utah.

In the study, Adams evaluated 33 horses immunized with a multivalent vaccine (Vetera Gold by Boehringer) containing Eastern and Western equine encephalomyelitis (EEE/WEE), tetanus, equine influenza, rhinopneumonitis, and West Nile virus (WNV).

She found no significant difference in immune response to the influenza vaccine between PPID horses and non-PPID horses of matched age. However, she did note significant differences in rhinopneumonitis and West Nile vaccine responses, with lessened antibody titers following immunization, in PPID horses.

In light of this research, Grubbs reported: “Make sure to maintain geriatric horses on regular vaccine programs and keep up to date with core vaccines (EEE/WEE, tetanus, WNV, and rabies). If there is a high risk of extensive travel or co-mingling of horses, then influenza and rhinopneumonitis vaccines should be boosted every six months.”

Author: Nancy Loving