Patchy Shedding

• Changes in temperature and daylight hours influence a horse's hair follicle growth and loss.horse 8 image by Harvey Hudson from Fotolia.com
  
  Complex hormonal actions regulate hair growth in horses. Individual follicles form a varied pattern of growth, transition and rest. Seasonal shedding usually happens over the course of several weeks, but sometimes the cycles become less coordinated. The coat can then take on a patchy look and even exhibit areas of baldness.
  
  

Stress

• The stress of pregnancy can cause horse hair to thin.appaloosa mare and colt image by Lee O'Dell from Fotolia.com
  
  Hair loss in horses can have a number of physiological causes. Stress from conditions such as pregnancy, chronic illness or even a change in environment can cause horses to lose hair and exhibit bald spots. The condition should resolve itself once the contributing factor is removed.
  
  

Skin Problems

• Ringworm lesions can leave bare spots in a horse's coat with hair often coming in lighter after healing.Horses Grazing image by ne_fall_photos from Fotolia.com
  
  Hair follicle infection, dermatitis, mites and parasitic fungi, such as ringworm, are among the more common conditions affecting skin health in horses that also can lead to hair loss. Diagnosing and treating any suspected skin condition early is important to avoid secondary skin infections and more serious lesions and loss of hair.