Written by Johanna Watson, DVM, Courtesy of UC Davis
Aging in itself is not a disease. However, aging predisposes the body to disease as parts become worn and the immune system is not as strong as it once was.
The diseases described here can occur in younger horses but their incidence increases with age. A horse may have more than one of these diseases concurrently, in which case it is important for a veterinarian to consider the potential disease interactions when deciding on a management or therapeutic plan.
Equine Cushing’s Disease
Equine Cushing’s Disease, a disease of the endocrine system, is one of the most common age-associated diseases in the horse. It is classically characterized by a long and/or wavy hair coat that does not shed appropriately in the spring. Horses can also be affected with this disorder prior to showing the hair coat change. Other clinical signs of this condition include laminitis, loss of muscular body mass, lethargy, increased water consumption and thereby increased urination.
Cushing’s Disease is caused by a loss of control by the pituitary gland which in turn causes overproduction of pituitary peptides. Tests are available to confirm a diagnosis. Once confirmed, daily treatment with pergolide replaces the normal control function of the pituitary tissue. Many of the clinical signs often subside with treatment.
Horses that have been athletic performers in their lifetime develop some form of arthritis. If a joint problem is bilateral and affects both the front or hind limbs equally, it may be difficult to detect and may be manifested only by stiffness or a reluctance to lie down.
There are many ways to treat lameness in an older horse, and which treatment to use will depend on the joints that are affected. For example, if a horse has bilateral arthritis of the hock joints and is stiff in both hind limbs, one option would be to inject both hocks with anti-inflammatory agents. This procedure often provides an animal with up to 6 months of pain relief and improved mobility. For a horse with chronic laminitis that has pain in both front feet and is tender-footed, shoeing the animal with front shoes only, with or without pads, may provide significant pain relief.
Other options for arthritis pain include oral anti-inflammatory drugs such as phenylbutazone, which can be given daily or as needed for discomfort. Note that since these drugs also affect the intestine and kidney, they should always be used cautiously and under the direction of a veterinarian. Some studies have shown beneficial effects from feeding chondroprotective agents such as glucosamine and chondroitin sulfate. However, these substances are more likely to be of benefit in the early stages of disease. Once significant bony changes occur in a joint, the benefit of such substances is likely to be minimal.
Changes in Digestion/Nutrition/Teeth Problems
Older horses, like older people, develop changes in their gastrointestinal system. Generally, these changes consist of a decrease in the digestibility of some feed components and a decrease in the absorption of some nutrients. As a result, the older horse requires a highly digestible, good-quality feed.
Along with these changes in the GI system, the equine teeth are going to wear out in the late 20s or early 30s, depending on how well the teeth have been cared for throughout an animal’s life. At this time, the reserve crown will be negligible, and the premolars and molars will begin to fall out. It is extremely important for older horses to have a complete oral exam at least twice a year. Loose teeth often remain in the socket because an older horse does not open its mouth wide enough for the tooth to fall out. Loose teeth and sharp enamel points can be removed during the dental exams.
As horses lose their dentition, they need to transition off of hay entirely as their primary forage source. There are many choices of complete feeds formulated for geriatric horses. With knowledge of your horse’s specific needs, your veterinarian would best be able to select the best one.
Colic is a disease affecting horses of all ages. However, there is a disease associated with age that can cause colic. Older horses are more likely to develop a benign fatty growth called a lipomain their abdomen. This lipoma can grow on a stalk that elongates, dropping the ball-shaped lipoma into the abdominal cavity. As the lipoma grows, it gets heavier and the weight of the mass tends to lengthen the stalk from which it hangs. The problem occurs when the stalk wraps around a portion of the intestine and tightens. This is known as a strangulating lipoma and requires surgical correction. Unfortunately, there is no way to detect these growths prior to their causing colic. Very often the colic associated with a lipoma is extremely painful. Surgical correction for this usually involves removal of a section of the intestines that was trapped in the stalk of the lipoma and then reconnection of the remaining intestines.
Older horses are more likely to develop cancers of various types. Horses with less pigment on the head or other regions may develop squamous cell carcinoma, a type of skin cancer. This is very common around the eyes of bald-faced or light-skinned horses. The grey horse may develop multiple melanomas over time. Any horse may develop lymphosarcoma, a cancer of the white blood cells that can affect almost any tissue in the body but commonly affects the intestines, chest or central nervous system. Early detection of all of these tumors provides the best options for treatment and outcome.
Here, the horse has a huge advantage over their human partner. The multitude of diseases that plague humans such as hardening of the arteries, high blood pressure and heart attack are virtually unheard of in the horse. However, over time the valve leaflets in the equine heart change and become stiffer. This change can lead to leaks in the valve and development of a heart murmur. The most common age-related murmurs are those of leaky mitral or aortic valves. The presence of a murmur in and of itself may not necessarily be cause for alarm but it must be monitored for change over time. A heart murmur is something that a veterinarian should check for during an exam. If there is any uncertainty as to the severity of a murmur, the size and velocity of the leak can be measured by a cardiology ultrasound. If the murmur changes dramatically, becomes very loud, or the horse develops signs of heart failure, then the animal should be re-evaluated by ultrasound as soon as possible.
Horses can develop changes in their lenses that cause them to opacify and become a cataract. As the cataract matures, the horse may lose its vision in the affected eye. While cataract removal is performed with limited success in foals, it is not often attempted in the adult horse because the procedure has been less successful with more serious side effects noted. Most often the changes that occur with age in the equine eye are associated with long-standing recurrent uveitis or “moon blindness” and so it is very important to recognize, treat and monitor these horses for recurrence of signs.
Urinary Bladder/Kidney Infections
Urinary bladder or kidney infections can occur at any age but older horses may be more susceptible to them due to age-related body changes or other disease conditions. In females, there are age-related conformational changes that occur as a result of loss of fat and muscle tissue. These changes make it easier for bacteria from the feces to gain entry into the urinary tract. Clinical signs of a urinary tract infection may include frequent urination, urine scalding of the hind legs, and blood in the urine. An older horse with Cushing’s Disease has decreased ability to defend itself from infection and thus may be more prone.
Older horses have older kidneys that may have lost some capacity over the years. Many of the drugs that we administer to alleviate pain and stiffness in the joints—nonsteroidal anti-inflammatory drugs—can damage the kidneys. It is advisable to do routine laboratory tests of kidney function in older horses before starting them on these types of drugs and to monitor them at intervals if they are on these drugs for long periods of time.