Are other horses shedding like mad while yours remains woolly? Are there patches of hair that refuse to budge? Has the coat taken on a stark mustard-like color? If so, you have delayed shedding.
In older adults, the most common cause of delayed shedding is PPID – pituitary pars intermedia dysfunction, aka Cushing’s disease. The coat may also be curly and long “guard hairs” may be present on the head or belly. PPID can have serious consequences including impaired immunity, muscle loss, tendon/ligament breakdown, diabetes and laminitis. If you suspect this, get your veterinarian involved. The treatment is the medication pergolide.
Parasitism can cause delayed shedding and is a particularly common cause in foals. Foals normally shed their baby coat within 3 to 4 months. The body gives nutrient preference to the key organs. As a result, alterations in the coat (and hooves) are common outward manifestations of the disrupted nutrient supply caused by parasites. This is also often accompanied by an abdominal girth out of proportion to the rest of the body. Treat with deworming drugs appropriate for the involved parasites and be sure to repeat a fecal exam 2 weeks after treatment.
Surgical removal of the thyroid gland to induce hypothyroidism delays shedding. A situation of similar severe hypothyroidism rarely, if ever, occurs under normal circumstances but thyroid function can be impaired in what is called “euthyroid sick syndrome”. In this condition, the stress of a chronic health problem causes the body to suppress thyroid function to lower metabolism and conserve nutrients for whatever the chronic challenge may be. It will improve spontaneously when the underlying problem is treated.
Thyroid function can also be impacted by deficiencies of iodine and/or selenium in the diet. Iodine is essential for the production of thyroxine hormone, T4. Selenium is needed to convert T4 to the active form, T3. Goitrogens in the diet can interfere with the utilization of iodine to manufacture thyroid hormones. These include nitrates from water or forage, raw soybeans, cabbage, kale, rape and turnips.
Horses that are stall-bound and getting little to no exposure to sunlight and exercise commonly are slow to shed. Light is a potent trigger and exercise improves blood flow to the skin and activation of sebaceous glands helps move out the old hair. Getting the horse out and moving is one of the best ways to speed up shedding.
Finally, malnutrition in general interferes with the normal cycle of hair production. There’s no problem in spotting an undernourished horse but deficiencies of specific key nutrients could also cause delayed shedding. These include essential amino acids, zinc, vitamin A, biotin (and other B vitamins in horses with intestinal disease) and omega-6 essential fatty acids.
If you notice delayed shedding, don’t ignore it. Consult your veterinarian and a nutritionist you trust to get to the bottom of the issue.
Eleanor Kellon, VMD