Horses of all ages may suffer from poor haircoat and skin condition due to poor nutrition, but aging horses may be especially susceptible. Good grooming and proper nutrition can go a long way toward addressing these conditions.
An older horse with a long haircoat that sheds late in the year, or incompletely, may be suffering from Pituitary Pars Intermedia Disease (PPID), commonly referred to as Cushing's disease or syndrome. PPID is caused by a tumor in the pituitary gland in the horse's brain. Symptoms include hirsutism (long haircoat), loss of muscle mass, and excessive drinking and urination. If you feel that your horse is exhibiting these symptoms, consult your veterinarian.
Horses with PPID may also exhibit insulin resistance and can benefit from diets lower in starch and sugars and higher in fat and fiber. However, veterinary care is essential for horses suffering from PPID.