Eliminate Pests

• Determine whether there are flies or other pests bothering your horse. Look for welts or hives that indicate the horse is irritated. Some horses may have hives on their neck and back, while others will have them under their belly. Runny, swollen eyes may also indicate the presence of flies. Spray your horse with fly repellent to see if this alleviates its desire to roll in the mud. But first consider that many horses roll for pleasure, not because they are irritated.
  
  

Sun Damage or Skin Irritation

• Check your horse's coat for signs of sun damage or sores that might be irritating it. The sun will dry out and lighten the horse's coat, especially on its back. Sores or fungus will cause the hair to thin or even fall out completely. Horses will roll to scratch these sore spots. Bathe your horse using an antifungal shampoo that contains sunscreen, and cover it with a light blanket. You can purchase sheets made specifically for fly and sun protection.
  
  

Proper Grooming

• Care for your horse properly when you finish riding. Horses like to roll in the mud to get rid of itchy saddle and bridle marks. Groom or bathe your horse until you can't see any marks. Use conditioner if your horse's coat is dry, and then spray your horse with a fly repellent. Stand with your horse while it dries before you put it back in its stall or pasture; a wet coat can also compel a horse to roll.
  
  

Check for Soreness

• Some horses roll in the mud to alleviate pain or stiffness in their backs. Watch your horse as it lowers itself to the ground. If it tries to roll but then hesitates several times or groans loudly, it may be in pain. Consult a veterinarian or horse chiropractor if this is the case. If your horse can roll from one side to the other without getting up, it's a sign that your horse has a strong, healthy back and simply rolls for pleasure.