Dear Dr. Gray,
    My 10 year old quarter horse developed hives about the size of a half dollar to a quarter ALL over his body.  He has never had hives before.  The other five horses on the farm do not have hives.  My vet put him on HistAll antihistamine at that time.  They went away in a week and then came back in two weeks.  I continued him on HistAll with minimal affect.  My vet pulled blood and sent it away to a lab in Arizona.  The allergy test came back that he is allergic to 17 things ranging from wool, at the top of the list, to willow trees.  We sprayed the field he is kept in for weeds and molds, which were six of the allergies.  We changed his hay to fescue because he is allergic to timothy, johnson, and orchard grass.  I have taken away all the possible things showing up on his allergy list.  However, we cannot keep him safe from the pollens and molds on the allergy list due to the weather and wind.  We have had him on flax seed meal, Spriolina, and BioZin with his grain and antihistamine with direction from my vet.
    The hives went away again in mid June for a week and then returned.  My vet gave my horse a shot of Dexamethasome (SP?) and capsules if needed.  The hives went away immediately, but returned five days later.  I started him on the capsules.  The hives went away after two days.  I stopped the capsules as told by my vet.  Five days later the hives started to return; I repeated the two days of capsules; hives gone.  I am waiting for the next five days to see what happens.  The hives return smaller and fewer each time.
    My vet suggests I start him on desensitizing shots prepared by the lab who tested him.  My vet says this process only has a 60% cure rate, but I should try.
    Is there another process or professional I can try?  We live in Fredericksburg, VA where it has been unusually hot and dry.  Many people are having hive trouble, but not this severe.  We moved here from southern VA 10 months ago, so I guess it is the region.
    HELP!  I would appreciate your opinions and suggestion.
        Thanks, S.S.

Dear S.S.,

Of all the skin conditions horses get, hives has to be one of the most difficult ones to deal with.  You almost need to be Sherlock Holmes to figure out what causes it!  On top of that, the medication regimen can be expensive and complicated and doesn’t always work or keep working.  And your poor horse looks and feels miserable.  You didn’t mention if yours was itchy as well as lumpy, but many are.

I like that you’re on products with omega-3 fatty acids, as research has shown they help maintain healthy skin and even improve certain skin conditions, like hives.  Until you can discover and remove the stimulus though, antihistamines and steroids will also be necessary.  You may want to ask your veterinarian if a different kind of antihistamine or steroid might work better in your individual horse.

Since your horse never had hives before you moved to this new area, it does sound like something in the new environment is causing this reaction.  The choices are many:  something in his diet, something he’s inhaling, something he’s coming in contact with, etc.  His hives could also be caused by a hypersensitivity to insects. 

You can either systematically eliminate potential causes one by one and wait to see if he gets better or you can attempt to diagnose the cause by testing.  Unfortunately, testing is controversial, as some feel the blood test your veterinarian has performed is not as useful as intradermal skin testing.  Before you start the desensitizing injections based on results of the blood test, talk to your veterinarian about the pros and cons of intradermal skin testing.  Or, ask him to help you get a second opinion at the nearest referral center, whether a private practice or University.

In the meantime, keep your horse as comfortable as possible.  Give frequent cool baths—with or without a soothing shampoo or other product—and protect him from insects with a fan in his stall and a mask, sheet and leggings during the day.