Dr. Amanda Adams from Merck Animal Health indicates that almost 30% of the horses in the U.S. are over 15 years of age, which is due to better veterinary care and better nutrition. However, we now have some problems in these horses that we did not have 30 years ago when the horse population was younger. As horses age, their immunity to fight off infection is not as strong. Because of this fact, older horses may also not respond to vaccination as well as younger horses. It has been shown that older horses, like older humans, are more susceptible to influenza than younger animals and humans even if they have pre-existing immunity. When vaccinating older horses, it is important to talk with your veterinarian as all vaccines are not the same and choosing one by cost is not a good plan.
In general, there are two types of vaccines: killed and modified live. Killed vaccines stimulate mostly antibody responses, while modified live vaccines stimulate cell-mediated immunity and antibody responses. The best vaccine for your horse depends on your specific situation and the specific disease you are trying to prevent. Your vet can help you make the best decision for your horse.
Another major problem of older horses is dental disease and only your veterinarian is capable of thoroughly examining your horse's mouth and making treatment recommendations. Equine dentistry is more than just floating the teeth. The condition of the teeth and the horse's overall health play a major role in recommending the appropriate feed. Some older horses have dental disease that requires x-rays to diagnose correctly, and untreated dental disease causes pain and can lead to sinus infections and bone disease.
The most common problems with older horses are obesity and endocrine diseases including equine metabolic syndrome and Cushing's disease. These diseases are complicated, but one important factor is to make sure your horse is not overweight. The reason this is so important is that many of these overweight horses are insulin resistant and have equine metabolic syndrome; many also have Cushing's disease. Both of these diseases lead to laminitis and founder, which is a painful hoof condition than can lead to permanent lameness and even death. Hopefully, your horses are being examined by your vet twice a year and these kinds of problems have been discussed. Testing is available for both these syndromes and treatment is also available. If your horse has either equine metabolic syndrome or Cushing's disease, it is critical to treat them before laminitis develops. If laminitis has already occurred, x-rays of the feet should be taken. Working with a farrier and a veterinarian familiar with treating this syndrome is necessary. I cannot stress enough how important early diagnosis of these diseases is in preventing pain and suffering in your older horse. And with Cushing's disease, your horse does not have to be overweight and may not have any clinical signs. If you have an older horse, ask your vet about screening for equine metabolic syndrome and Cushing's disease with a blood test for early detection of these serious diseases.