My 27-year-old horse is doing well for his age physically, but his behavior sometimes has me wondering whether his mind is “all there.” I often find him a corner of his pasture, looking confused. I know that horses slow down with age just as we do, but can they develop an equine version of Alzheimer’s disease? How would dementia look in horses?

Answer:

Dementia isn’t as well-characterized in horses as it is in people, or even other animal species. For example, “cognitive dysfunction syndrome,” which is akin to dementia, is relatively common  in geriatric dogs. In both people and animals, dementia is defined as a neurobehavioral condition that leads to progressive and persistent loss of brain function that impairs daily functioning. Brain dysfunction can include problems with memory, abstract thinking and social skills, such that affected individuals often have personality changes.

Horses can probably get dementia

While an equine cognitive dysfunction syndrome has not been described, my experience suggests that horses can get dementia. For example, there are many cases where horses with documented  behavioral changes are found to have neurodegeneration in their brains upon postmortem examination. Some of these horses are younger and are diagnosed with equine neuroaxonal dystrophy (eNAD)/equine degenerative myeloencephalopathy (EDM). Others are older and might have age-related cognitive decline.

Regardless of age, horses with neurodegenerative disease can show signs similar to those associated with dementia in people. Some become lethargic or  dull, appearing to lose interest in their environment. Others become anxious, agitated or aggressive toward people or other horses.

Signs of trouble

A common observation in horses with a final diagnosis of neurodegenerative disease is the development of uncharacteristic and unpredictable “spooky” behavior, often without an identifiable stimulus. Whether this reflects abnormal visual processing of information or even visual hallucinations is uncertain.

Owners, trainers, and caregivers also report that these horses have difficulty learning new tasks or movements. They may also forget things they once knew.  The horses might become challenging  to ride or even handle on the ground due to spooking or other bad behaviors. They may include bolting, bucking, rearing, spinning, difficulty crossing thresholds or changes in surface, or random stopping before jumps or other obstacles.

Horses with these types of behavioral changes can be difficult or even hazardous for their handlers and riders. Additionally, horses can develop behavioral changes for reasons other than brain disease. Most importantly, these can be associated with chronic or recurring pain or discomfort. Therefore, I recommend veterinary evaluation if a horse starts showing uncharacteristic behavior.

Amy Johnson, DVM, DACVIM

University of Pennsylvania School of Veterinary Medicine

New Bolton Center

Kennett Square, Pennsylvania

Amy Johnson, DVM, DACVIM, is the Marilyn M. Simpson Associate Professor of Equine Medicine at the University of Pennsylvania School of Veterinary Medicine New Bolton Center. After receiving her Bachelor of Arts degree from the University of Pennsylvania, Johnson earned her veterinary degree at Cornell University College of Veterinary Medicine. She carries board-certification from the American College of Veterinary Internal Medicine in both Large Animal Internal Medicine and Neurology.