AAEP Convention 2001: The Pruritic (Itchy) Horse

We've probably all had, or at least seen, a horse with an itching problem no one could quite figure out. In the roundtable discussion on pruritic (itchy) horses, veterinarians discussed just how to diagnose and manage these horses to keep them comfor  table and with an unblemished hide.

There are many causes of persistent itching in horses, but according to Susan White, DVM, MS, Dipl. ACVIM, professor at the University of Georgia and moderator of the session, "The main thing is to simplify diets. Today's horse is often not on one supplement, it might be as many as 14. We need to simplify the feed and limit topical products for these horses." Feed allergies are not exactly rare; White and other attendees have seen horses that quit scratching when molasses and sometimes long-stem hay were removed from their diets. Testing is needed to determine whether this is necessary.

To control scratching, "It's very important to use management as well as products," began White. For example, if a horse's worst problem is a sensitivity to insect bites, provide him with wind. Hang fans in the stall or run-in sheds where horses rest (should be out of sunlight) and direct them at all levels of the horse--at his legs and ventral abdomen as well as topline. This requires more than one box fan.

"I've had clients hang fans in the pasture run-in sheds," said White. "The horses find them immediately."

Another option is to find out to which insects a horse might be hypersensitive, then manage him accordingly. For example, if a horse has a problem with dusk or evening-dwelling mosquitoes, then you might want to turn him out in the daytime and apply fly repellent when you bring him in at night.

Fly repellent is definitely not a panacea, however; White estimates that 20-30% of the problem horses she sees are allergic to pyrethrins, a common class of insect repellent. Intradermal skin testing is quite useful for identifying such sensitivities, she added.

When diagnosing the cause of a horse's incessant itching, it is smart to make sure that a horse is off of steroids or any other medication that might affect his immune system's response to testing for at least three weeks. This is usually best done in the fall, or whenever insect activity in the area decreases.

Once the cause is diagnosed, then the owner and veterinarian should plan a management program to be in place before the next year's initial onslaught of insects.

Desensitization Therapy

Approximately 50-70% of horses respond favorably to a custom-made desensitization vaccine; however, six to 12 months is needed before the horse receives the full benefit of this therapy. Desensitization might give a very limited benefit to a prolonged one, depending on the individual (there is not enough research follow-up on treated horses to be sure). Also, since at least some horses will need treatment for life, if a particular horse responds well to treatment, most owners are not willing to stop therapy.

The vaccine is injected from once every two days to twice a week during the initial desensitization, then maintained at one injection per week. The cost of the desensitization to the owner generally runs about $300 per year (not including the initial testing procedure).

Steroids?

Another treatment option is steroid use to minimize the body's immune response to the cause of the itching. Some people are concerned about an increased risk of founder with dexamethasone, but there is no black and white answer to this risk. However, most people are cautious with steroids for horses that have foundered before, or with horses at especially high risk, i.e., an aged overweight horse with poor feet.

Management Tips

Tips for owners from this session include:

  • Minimize topical repellents when possible,
  • Use only repellents labeled for horses, 
  • Keep horses clean without washing them so much that there is over-drying of the skin (which can worsen itching), and
  • Minimize horses' exposure to whatever is causing their individual problems--i.e., keep horses with pruritis out of direct sunlight.

About the Author

Christy M. West

Christy West has a BS in Equine Science from the University of Kentucky, and an MS in Agricultural Journalism from the University of Wisconsin-Madison.

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