Immune Issues in Older Horses

The immune system of a horse often becomes less efficient as the horse grows older.

As horses enter their Golden Years, their immune systems begin to wane and they aren’t able to fight off diseases and parasites as well as they did when they were younger. Getty Images

“It is important to keep the older horse vaccinated, just like you do the younger horses. You want to keep the immune system as strong as you can,” said Tia Nelson, DVM, a veterinarian who is a horse owner and practitioner near Helena, Montana. There might be a few contagious diseases that you don’t have to worry about vaccinating for, however, if it’s an older or retired horse that never leaves the farm and never comes into contact with other horses.

“If you can keep older horses basically healthy and vaccinated, appropriately dewormed, supply good nutrition and try to minimize stresses (exposure to extreme weather, overwork, emotional stresses, etc.), they generally don’t have major immune issues,” said Nelson. 

The immune system of a horse often becomes less efficient as the horse grows older. Therefore, the geriatric horse might be the one that gets herpesvirus or some other disease when it goes through the barn.

We might also see a surge in parasite egg numbers in older horses. This is another aspect of a diminishing immune system—less resistance to parasites. The older horse might need to be dewormed more often. It pays to monitor the worm burden in the older horse (and this can be done with fecal egg counts), especially if the horse is out on pasture—which is where he will be most likely to pick up the parasites.

Another manifestation of a waning immune system is the increased frequency of cancer in geriatric horses. Melanomas on gray horses frequently begin to proliferate as the horse gets older. Squamous cell carcinomas might develop in areas of unpigmented skin such as around the eyes, prepuce and vulva. Internal tumors might also develop, resulting in weight loss and other signs specific to the body system affected. 

An annual physical exam offers your veterinarian the opportunity to determine if your aging horse needs additional attention in preventive medicine, parasite control, weight maintenance or other areas affected by the aging process.

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