You might not have heard the word “immunosenescence,” but if you’re caring for an older horse, you’re dealing with it daily. It seems that aging isn’t just a matter of time marching on for the horse as a whole; the immune system itself is also aging biologically via this process.
As horses age, their systemic immunity declines, which can contribute or lead to increased prevalence of cancer, autoimmune and chronic diseases, poor response to vaccination, and increased susceptibility to common infectious diseases.
Amanda A. Adams PhD, a researcher at the University of Kentucky Gluck Equine Research Center, in Lexington, spoke on the topic at the 2016 American Association of Equine Practitioners convention, held Dec. 3-7 in Orlando, Florida. She explained research findings regarding how aging horses respond to vaccinations, inflammation, and parasites.
Another term you might not have heard is “inflamm-aging,” or chronic, low-grade inflammation that occurs with age. We normally think of inflammation as being acute, for instance, as with a swollen ankle. With treatment, that acute inflammation resolves in days, and the swelling subsides.
But in the aging horse, researchers have learned that something in the cells “turns on” the inflammatory process systemically, and it continues at a low level from that point on. This inflamm-aging process in humans contributes to arthritis, cancer, diabetes, osteoporosis, dementia, vascular disease, obesity, and metabolic syndrome. And it turns out, obesity might do the reverse, contributing also to the inflamm-aging process. Researchers in Adams’ lab are currently investigating the repercussions of inflamm-aging for the aged horse.
Researchers know that because of horses’ aging immune systems, these animals don’t respond to vaccinations as well as younger horses do. Similarly, older horses have higher parasitic fecal egg counts compared to middle-aged adult horses, which could be in part due to the decreased immune response with age, thereby changing their resistance to parasites.
Add to those problems, 20% of horses over 20 years old have pituitary pars intermedia dysfunction, or PPID (historically referred to as equine Cushing’s disease). PPID is a progressive and debilitating endocrine disease and, not surprisingly Adams and colleagues are finding that affected horses could have a further reduced immune response to vaccination.
Adams has researched various ways of combating these problems, with emphasis on nutrition and supplementation that might have immune-modulating benefits. In fact, she found that good nutrition, along with prebiotics, reduced inflammation and improved immune responses to vaccination in older horses.
She emphasized the importance of keeping older horses up to date on vaccines and even consider boosting with some of the risk-based vaccines every six months if the older horse is traveling or exposed, such as in the case of West Nile virus during a long mosquito season. This is important given previous research in which Adams found that when exposed to flu, unvaccinated older horses got sick, even though they might have had a flu vaccine years earlier. Vaccinated older horses did not get sick with flu.
Since we know older horses need improved immune support, a good wellness plan for seniors should include twice-yearly health exams and fecal egg counts, routine dental exams, body condition scoring, nutritional evaluations, endocrine screening for PPID and insulin resistance, and a regular vaccination schedule.