“DESPITE THE GROWING BODY OF RESEARCH INTO SENIOR HORSES’ HEALTH, THE EXACT CAUSES OF DEATH AND THE MOST IMPORTANT DISEASES THAT OLDER EQUIDS SUFFER FROM REMAIN POORLY DOCUMENTED.”
By Stacey Oke, DVM, MSc

Thanks to improved equine management and husbandry knowledge, along with committed owners, horses are now living longer and healthier lives than they have, on the whole, in the past. Still, as much as we’d like our horses to live forever, they all will pass on to greener pastures eventually.

Despite the growing body of research into senior horses’ health, the exact causes of death and the most important diseases that older equids suffer from remain poorly documented. In fact, “old age” alone is often listed as the reason for death or euthanasia.

“To provide better care to aged horses, we need a better understanding of what diseases they suffer and to determine the actual cause of death rather than simply ascribing it to old age,” explained Margaret (Peg) Miller, DVM, PhD, from Purdue University’s Department of Comparative Pathobiology and Animal Disease Diagnostic Laboratory in Indiana.

To that end, Miller and colleagues conducted comprehensive post-mortem examinations on 241 horses that were 15 years of age or older. They found that:

• The most common cause of death in aged horses was diseases of the digestive system, with this diagnosis being made in almost 50% of horses;
• The next leading causes of death were attributed to the pituitary gland (12.9%); locomotor system (10.0%); nervous system (7.9%); cardiovascular and urinary systems (4.6% each); and reproductive, respiratory, and integumentary systems (4.2% each);
• Neoplastic disease (cancer) was the underlying cause of death in 18.7% of horses. The most common types of cancer included squamous cell carcinoma, lymphoma, and melanoma; and
• Pituitary pars intermedia dysfunction (PPID, or equine Cushing’s disease) was the most commonly made specific diagnosis. PPID was the reason for euthanasia of 47.7% of the 65 studied equids with PPID. Other reasons for death or euthanasia in horses with PPID included colic, lameness, and cancer.

“This study also found that aging horses, particularly those with PPID, often suffered more than one debilitating condition, such as neoplasia, infection, lameness, and recurrent airway obstruction (heaves),” relayed Miller.