The Aging Horse
There are a number of ways to add calories to an older horse's diet to help him keep his weight up.
Photo: Anne M. Eberhardt/The Horse
Your 20-year-old gelding is starting to look like a senior citizen; there's more sway in his back and less bounce to his step. Horses generally don't become senile or as physically frail as elderly humans, but their bodies go through a number of physical changes as they grow older.
Julia Wilson, DVM, Dipl. ACVIM, of Turner Wilson Equine Consulting LLC, in Stillwater, Minn., says horses experience both external signs of aging as well as internal changes. The gastrointestinal (GI) tract, heart, immune system, and other body systems might not function as efficiently as they did when the horse was younger.
Debra Powell, MS, PhD, associate professor at The Ohio State University Agricultural Technical Institute, says most people consider old age in horses to be 18-plus.
"Some individuals age more quickly or slowly, depending on physiologic conditions," she explains. "Some show signs of aging as early as 16, and some don't look old until they're in their mid-20s. We see more evidence of aging problems today, just because horses are living longer, thanks to good care. Life expectancy has increased." She adds that some horses age more quickly simply due to genetics.
In this article we'll explore how the horse's various body parts and systems age and what to look out for in your equine senior citizen.
Often one of the first signs of aging is a dip in the back; the withers become more prominent and the "saddle" area sinks. "This is due to weakening of the supraspinous ligament that supports the back," explains Powell. As the back sinks, some horses lose muscle mass as well. The withers and back then become bony, which can lead to saddle-fitting issues.
Ashley Boyle, DVM, Dipl. ACVIM, an assistant professor of medicine in the field service section of the University of Pennsylvania's New Bolton Center, says that even if the horse is well fed, his body condition changes as he loses muscle mass; some muscles atrophy with age. "He won't have as much muscle along the withers and back as he had at a younger age," she explains. "One reason for this can be related to endocrine disease. Protein metabolism may result in muscle atrophy. Another reason, if the horse is retired, is lack of use. Muscles become smaller and less strong, just as they do in an older, inactive person. This also plays a role in ligament strength (in the topline region)."
Tendons and ligaments also lose strength and tone in other areas of the body. "In some breeds and individuals there may be dropping of the fetlock joints (especially in the hind legs) due to degeneration of the suspensory ligament (which extends down the back of the lower leg from the knee or the hock and lies between the flexor tendons and the cannon bone before connecting to the sesamoid and pastern bones)," says Wilson.
Further physical signs of old age include drooping lips, more obvious hollows above the eyes, and more gray hairs--especially around the face and eyes. Hair coat might become dull, and the horse might be slower to shed his winter hair coat in the spring. "This may be a sign of equine Cushing's disease or pituitary pars intermedia dysfunction (PPID)," explains Wilson (learn more about these conditions on page 26).
The horse might also change his movement, especially if his joints have become stiff due to arthritis. More on this in a bit.
Horses' teeth continually push up from the root to make up for wear from chewing. Also, teeth elongate and incisors angle forward as horses age--giving them a characteristic senior appearance. Molars might develop hooks and ridges, and these sharp points can interfere with the horse's proper grinding and chewing motion. As the horse loses his ability to chew, obvious weight loss might result. Teeth might wear out faster, however, in some horses than others. "Perhaps the enamel is not as strong, or the teeth are pushed out of the jawbone at a different rate," says Wilson.
Boyle recommends having a licensed veterinary dental provider conduct annual or biannual dental exams once a horse reaches geriatric age to avoid dental problems. "Some horses need regular work on their teeth if they have a poorly balanced mouth or did not have appropriate care in earlier years," she says.
She points out that since the teeth are continually erupting from the gums, at some point a horse might run out of reserve crown. "As the horse becomes very old, some teeth may fall out," says Boyle.
Complicating occlusion, "If a horse loses teeth, the opposing teeth grow abnormally," adds Powell. These horses might require feed that is chopped up and processed or softened because they can't chew effectively. And, according to Boyle, these chewing-challenged older horses with lost teeth, an unbalanced mouth, or sharp, painful hooks and points are prone to esophageal choke.
Hearing and Vision
Hearing loss is fairly rare in older horses, according to Boyle. "When we find hearing loss in a horse it's generally the result of a neurologic condition," she explains. "The nerve associated with hearing is affected. Hearing loss solely due to aging is not usually recognized clinically."
Vision quality in the older horse also cannot be characterized as well as in humans. "One of the more common causes of vision loss is uveitis (also known as moon blindness; the most common way horses get cataracts is secondary to uveitis), and this can happen in younger as well as older horses," Boyle says.
Very rarely, Cushing's disease can be a factor in vision loss. "Cushing's has a pituitary origin in horses, in a gland at the base of the brain," says Boyle. "Some of these horses have an enlarged section of the pituitary and this can press on the optic nerve. Vision impairment is a rare clinical sign in Cushing's disease, but is possible."
Many horses develop arthritis as they age, especially if they've had an active career. There is wear and tear on joints, and cartilage might start to fail. "This may evolve into osteoarthritis, even if there's no original pathologic condition involved," says Boyle. "Conformation can play a role; a horse with crooked legs is likely to have more arthritis because there's more strain on certain parts."
Good farrier care can help reduce stress on joints and help prevent problems to some degree, or alleviate some of the strain. "If the load on the foot is inappropriate, like an underrun heel, this puts more strain on joints further up the leg and may cause more problems or irritate the arthritis that's already there," says Boyle. Consistent and proper hoof care throughout the horse's life can prevent problems later or reduce their severity.
Due to stiffness and pain, older horses might not be able to hold their feet up very long for trimming or shoeing. Therefore, the farrier should work on each foot quickly and briefly, rotating from one limb to another (or working on another horse between trims/shoeing sessions) instead of keeping one foot off the ground very long.
We often think about wear and tear on leg joints, but arthritis can also affect other joints in the body. "Some horses get arthritis in the neck, just like people do. A few develop neurologic issues if arthritis in the neck becomes severe," says Wilson.
"Arthritis in the neck may impact the spinal cord and/or put pressure on spinal nerves where they come out between the vertebrae," she continues. "This may lead to wobbler-type signs (cervical vertebral stenotic myelopathy). If a nerve gets pinched where it comes out of the spinal column, the horse may develop lower motor neuron signs. The impulses are damaged after they've exited the spinal cord, and you see areas where muscle mass is diminished. The horse may sweat abnormally in these areas." Intra-articular injections in the neck facet joints might help these horses.
The GI tract might also lose efficiency as a horse ages. "With some older horses, it's almost impossible to keep weight on them, even when feeding a senior diet with high fat content," says Wilson. "Their teeth are not as good anymore, and food starts to go through without being digested very well. You start to see sloppy stools and loose manure," she says. Some geriatric horses can no longer handle the roughage content of their diet and develop chronic diarrhea. This might be due to chronic parasitic damage to the large intestine. Using senior feeds designed as complete feeds sometimes helps in these cases, if introduced to the horse's diet slowly (see page 43 for more information about senior horse nutrition).
Colic can also be an issue in the older horse due to a variety of factors including more sluggish gut motility or other digestive tract changes, increased parasite load, or tumors. Motility issues might cause impactions, especially in the cecum and colon, which generally are more common in older horses, says Boyle.
In broodmares and stallions alike, fertility drops with age. "Semen quality in stallions goes down, and it may also become more difficult for them to breed mares (via live cover) if they have arthritis," says Wilson. Reproduction becomes impossible as horses pass a certain age, but the actual end point varies from horse to horse.
"Horses tend to get some valve degeneration over time," says Wilson. "Most of them will be fine, but some end up with diminished performance capacity. A small proportion may develop atrial fibrillation (an abnormal heart rhythm that involves the upper two chambers, or atria, of the heart) or some kind of heart failure. Horses may also experience deterioration of the aorta."
Peter Physick-Sheard, BVSc, MSc, FRCVS, veterinarian and associate professor in the University of Guelph's Ontario Veterinary College Department of Clinical Sciences, says horses don't have heart attacks or get coronary artery disease like humans do, but some heart issues can impair the older horse's ability to work. "The horse may have a mild cardiac problem that was of no consequence when he was young, or not working at peak capacity, but it may eventually reach a point where the heart condition starts slowing the horse down," he says.
Many horses have leaky heart valves that cause "murmurs," but most of these are not serious, especially if the horse is not pushed hard physically.
"The possibility of heart problems is one reason I recommend having your veterinarian do an annual physical examination for any horse, especially if you are still riding that horse," Wilson says. Some of these degenerative changes might be picked up at that time.
Owners are often surprised when their older horse that hasn't been off the farm in years gets an infectious disease. Because the immune system becomes less efficient as it ages, "the geriatric horse may be the one that gets herpesvirus when it (the virus) goes through the barn, or strangles, or some other disease," says Wilson.
"You may also see a surge in parasite egg numbers in older horses," says Powell. Less resistance to parasites is another aspect of a diminishing immune system.
"For the older horse, your veterinarian might recommend more frequent fecal checks, to see if parasites are a problem, and could then advise as to which product and when to deworm that horse," suggests Boyle. "The fecal float (fecal egg count exam in which, when placed in a chemical solution, the manure sinks and the eggs float) may be more expensive than the dewormer, but there's no point in deworming the horse more frequently unless there's a need." Also, in the long run you'll likely be saving yourself money.
"One manifestation of a waning immune system is the increased frequency of cancer in geriatric horses," says Wilson. Melanomas on gray horses begin to proliferate; squamous cell carcinomas develop in areas of unpigmented skin, such as around the eyes, prepuce, and vulva; and internal tumors might develop, resulting in weight loss and other signs specific to the affected body system.
Powell says older horses have more potential to develop tumors in the thyroid, adrenal, and pituitary glands, as well as GI tract polyps. "Some melanomas are internal, and you don't see them," she adds.
"Sometimes we see lipomas in older horses--the little fatty abdominal tumors on a long stalk," says Wilson. "These can occasionally wrap around the intestine and create blockage, necessitating surgery."
"Unfortunately, a lot of 'retired' horses get turned out on the back 40 and no one pays much attention to them," says Wilson. These horses might develop a problem before the owner notices. As a horse goes through physical changes with age, he needs good care and careful attention to his condition to ensure you can help make his retirement years as comfortable and healthy as possible.
About the Author
Heather Smith Thomas ranches with her husband near Salmon, Idaho, raising cattle and a few horses. She has a B.A. in English and history from University of Puget Sound (1966). She has raised and trained horses for 50 years, and has been writing freelance articles and books nearly that long, publishing 20 books and more than 9,000 articles for horse and livestock publications. Some of her books include Understanding Equine Hoof Care, The Horse Conformation Handbook, Care and Management of Horses, Storey's Guide to Raising Horses and Storey's Guide to Training Horses. Besides having her own blog, www.heathersmiththomas.blogspot.com, she writes a biweekly blog at http://insidestorey.blogspot.com that comes out on Tuesdays.
POLL: Mosquito-Borne Diseases