There are many options for treating arthritis. For the horse with single joint problems that can be pinpointed, local treatments are available. However, most old horses have multiple joints with arthritis all at once, often in inaccessible regions such as the hip, or neck.
The best option is the judicious use of pain killers or anti-inflammatories. Examples include phenylbutazone, Banamine® (flunixin meglumine) and ketoprofen. Eventually it becomes difficult to get enough of these painkillers into the horse without causing side effects, including loss of appetite, gastric ulcers, weight loss and diarrhea. You should talk to your veterinarian about a schedule of treatments to soften that possibility. Cartilage protective agents should also be considered at this point, for example chondroitin sulfate and polysulfated glucosaminoglycans (PSGAGs), which are available as supplements or injections.
This causes obvious signs of heel pain, and is easily managed early in life with corrective shoeing and oral medications, or in some cases, by surgery ("neurectomy"). The choice to perform neurectomy (to "nerve") an old horse depends on what other problems exist, and must not be done without serious consideration of potential complications.
Orthopedic (arthritis, navicular) problems are untreatable:
Economics obviously plays a role here as well, since anti-inflammatory and cartilage protective agents, if used, can be expensive. Determining when arthritis is a consideration for euthanasia is most difficult, because the problems are long-standing, so get another opinion and step back.
Heart Valve Disease
Heart murmurs are a dime a dozen in old horses, but they are mostly benign. However, with the procession of years, the heart valves start to "wear out." The valves most commonly affected include the aortic and mitral valves, because they are under the most stress. They function to control blood flow through and out of the left ventricle, the part of the heart that pumps blood to every place in the body except the lungs.
When these valves become leaky, you can see back flow of blood within the heart on ultrasound, which ultimately causes the heart to fail due to inadequate delivery of blood, and therefore oxygen, to tissues. This is one reason that it is common to detect heart murmurs in old horses, although many are inconsequential and do not require further attention.
An ultrasound examination ("echocardiogram") provides information that will forewarn you if the murmur is serious. If a loud murmur should arise, it should be checked then rechecked at no more than 6 month intervals. If it gets louder or there are signs of poor heart function (poor pulses, lethargy, dark mucous membranes, increasing breathing rate), it should be treated. If the heart is rechecked by ultrasound, the cardiologist can see how fast the problem is progressing, and help you prepare for a downturn in quality of life if that seems imminent.
Symptoms of heart failure include: a horse with a loud murmur that is lethargic, dropping weight, reluctant to move, stocking up, accumulating edema on the belly, disinterested in food, exhibiting frequent restlessness. Also, poor pulses, visible pulses in the neck, bluish or dark mucous membranes, increased breathing effort, or froth from the nostrils are present. These symptoms need to be addressed right away, and may be treatable for a period of time, usually no more than a few days to weeks.
Kidney failure is a problem that most horses face if they live long enough, and it is a major cause of unexplained weight loss. The disease can be recognized by the following symptoms:
A urinalysis, ultrasound of the kidney and perhaps a biopsy should be pursued to evaluate the extent of the problem. As you can see, there are many causes of weight loss in the older horse, so a thorough evaluation is necessary in every case.
"Broken wind, COPD" is extremely common in the older horse. Up to 20 percent of horses get heaves, and it can be highly debilitating and even cause sudden death. Fortunately, there are great options for the horse today, including hypo-allergenic hay, pelleted feeds to replace hay (since these horses are ultra-sensitive to mold found in hay), and oral and inhaled medications. If the environment can be managed diligently, and the horse put on medications without side effects, horses rarely die from heaves today. They may, on the other hand, not be used for riding.