Special Considerations for the Aged Horse
Dr. Andrew Hoffman and Dr. Philip Johnson
A thick coat that doesn't shed out ("hirsutism")
Dental problems often cause persistent pain and loss of function such as chewing difficulties and poor digestion. The horse's cheek teeth are continuously growing but at the same time they're being worn down by the action of chewing. This is one reason that horses can no longer cope in nature. As the cheek teeth wear down there is increased risk for other tooth problems such as tooth root abscesses, periodontal (soft tissue) disease and sinusitis, that can be very painful.
Dental care is important for aging horses, and you can reduce the risk of health problems due to dental disease with routine dental care and switching to a diet that does not require a significant amount of grinding action. Still, however, horses without teeth, even when fed purees, mashed carrots and tonics, have problems maintaining their body weight, and once they are drained of body fat and show the ribs, the process can be very difficult to reverse.
Horses that have lost weight to the point where their ribs or back are prominent, will take at least six months under ideal circumstances to return to weight on full feed. This can be extremely difficult to achieve without good teeth. In general, horses with serious lack of teeth that lose weight despite your best efforts to feed them, may have difficulty surviving any change in environment, stresses, or new demands.
Equine Cushing's Disease (ECD)
Cushing's disease causes loss of function of the hormonal system and may not respond to treatment. Many older horses develop ECD, which is caused by a growth on the pituitary gland located at the base of the brain. This very active growth releases a hormone that causes the adrenal gland to be hyperactive and to produce excessive amounts of steroid hormones. The resulting symptoms include:
Progressive weight loss
Excessive drinking and urinating
Sweating and unusual dampness of the coat
This condition also leads to reduced ability to fight infections, so older horses with ECD are prone to infectious diseases such as EPM, tooth root infections, sinusitis and common respiratory infections. There are special tests to support the diagnosis and specific treatments, so it is well worth having a workup for this problem. If untreated, horses with ECD get progressively thinner, dehydrate, founder or suffer chronic infections that don't respond well to antibiotics.
In general, it is the complexity of secondary problems that may become untreatable. For example, severe laminitis, pneumonia or severe sinusitis, which cause pain and interfere with breathing and eating, are serious and possibly irreversible. Weight loss may also be too rapid to reverse. In some horses, the pituitary gets so large it actually puts pressure on the hypothalamus, that part of the brain that regulates "flight or fight" responses, emotions, thermoregulation and other hormonal functions. The horse cannot maintain his body temperature or he has seizures.
Failure of The Immune System
One reason old horses do not respond to conventional treatments is failure of the immune system brought about by old age. Treatment of infections in older horses must be aggressive and often requires a combination of antibiotics, which can be expensive. While it's always worth treating an infection, a lack of response is a cardinal sign that the "back-stop" function of the immune system is failing.
Like people, older horses are prone cancer, which causes pain, loss of function and lack of response to conventional treatments. Old gray horses invariably develop melanoma of the skin. Other common cancers include lymphosarcoma, squamous cell carcinoma ("cancer eye"), and fibrosarcomas. At the present time, there are not many options for treating cancers in horses, since radiation and chemotherapy are extremely expensive or not feasible because of the size of the animals.
If the cancer is localized to one area, there are possibilities, although they may be expensive, of local treatment with cryotherapy, surgery, and/or local injection of chemotherapeutic agents. Most of the time, however, cancer is a life-threatening disease without many options. Tumors often cause extensive local damage making organs dysfunctional such as the loss of swallowing ability (mouth, tongue and esophageal tumors), interference with breathing (nasal, tracheal or lung tumors), digestion (intestinal tumors), urination (bladder, genital tumors), defecation (melanomas of the tail), or even walking (spinal tumors). If any of these areas are affected to the point where the horse is in constant pain, experiences serious weight loss or organ system failure, the condition may not be treatable.
Inefficient Intestinal System
Along with the relative decrease in the effectiveness of the aged horse's cheek teeth, the intestines of older horses appears to be less efficient at digesting their food. This is why some horses appear to be dropping weight slowly, despite feeding them more. Before assuming this is the problem, the intestinal absorption of the horse should be tested, and a complete blood chemistry panel and hormone analysis performed.
The problem of age-related poor intestinal digestion may not be hopeless, in that diets higher in proteins and calories can offset the eventual progression of weight loss. If there are other coexisting causes of weight loss (e.g. dental disease or kidney failure), this can be serious, because you just will not be able to get enough food into the horse to keep up. If despite your efforts to push the feed, the horse continues to lose weight, this could become very serious once the horse is ribby, especially for maintaining body temperature in the winter, and fighting off any stresses or infections that are encountered from time to time.