Age can complicate managing already tricky metabolic diseases in horses

Metabolic diseases, including both insulin dysregulation (ID) and pituitary pars intermedia dysfunction (PPID, previously known as equine Cushing’s disease) occur commonly in horses. Estimates indicate approximately 20% of horses 15 or older have PPID, while the prevalence of horses with ID or a combination of ID/PPID remains unknown.

The most important pathological—involving disease or damage—condition of both ID and PPID horses is laminitis, referred to in this setting as endocrinopathic laminitis or hyperinsulinemia-associated laminitis (HAL). As with other forms of laminitis, horses with HAL suffer extreme pain, lameness, and compromised quality of life.

Rather than delving into the clinical signs and diagnosis of ID and PPID, we’ll move beyond the basics in this article, focusing on best practices for managing aging horses with ID, PPID, or both. The key areas of management we’ll describe include diet and exercise tailored to aged horses, as well as medications. Special consideration also goes to managing older horses with osteoarthritis (OA) and understanding end-of-life care.   

Feeding Aging Metabolic Horses

Without a doubt, diet is the cornerstone of managing metabolic horses to decrease postprandial (after meals) hyperinsulinemia, even if the horse is not overweight.

“It is crucial to limit nonstructural carbohydrates, which are the sugar and starch components of the diet, in horses with ID to control postprandial hyperinsulinemia,” says Erica Macon, MS, PAS, PhD, of the Department of Animal Science at Texas A&M University’s College of Agriculture and Life Sciences, in College Station.

Scientists derived original recommendations of feeding commercialized concentrates and hay with less than 12% NSC from research in healthy horses, and they theorized this level would be safer for horses with metabolic disease. Since then, Macon and other nutritionists have recommended low-NSC hays, decreased pasture access, and ration balancers.

“However, it’s important to recognize that individual horses may have different insulin responses to the same diet,” says Tania Sundra, BSc (Hons), BVMS, MANZCVS (equine medicine), of Avon Ridge Equine Veterinary Services, in Brigadoon, WA, Australia. “Factors such as genetics and the gastrointestinal microbiome likely play a role in this interhorse variability, though this has not been fully elucidated. While some sources suggest a stricter threshold of 10% NSC, the 12% guideline is generally considered appropriate for most horses. Monitoring your horse’s insulin levels and adjusting the diet accordingly remains the best approach to managing horses with ID.”

Macon also points out that “nutritionists are trying to move away from percent-NSC basis. We now recommend that horses with hyperinsulinemia are limited to 0.1-0.15 grams NSC/kilogram body weight (BW) per meal