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Q: I’ve owned my 12-year-old 17hh Irish Draft/Thoroughbred for two years and we participate in riding club activities. He has no history of illness but earlier this year he developed what looked like an allergic reaction on his front and hind legs. This was accompanied by some fluid retention in his lower leg, which disappeared with exercise.

My vet is perplexed by the condition, as it appears to give my horse no problems. Steroids reduced the swelling slightly, but it has now returned. He is out at grass and has one hard feed a day, including various supplements and carrots. Do you have any idea what it might be?

Jo Holmes MRCVS replies: It sounds as though your horse has an allergy to something in his diet or environment. At the age of 12, he is not too old to develop an allergy even to something his body has been tolerant of for years. The immune system can suddenly react adversely for no apparent reason.

I would start by eliminating all his hard feed for a month, including any supplements, and then, if an improvement is seen, reintroducing each component one week at a time.

You might also need to keep your horse off the pasture for a while, in case there is something growing in the field that has triggered his condition.

If he is stabled routinely, try changing his bedding to paper and consider feeding Spillers’ Readigrass rather than hay or haylage, as this is the closest thing to a hypo-allergenic roughage that I have come across.

The important point to remember is that you must only change one thing ata time to be sure of identifying the causative factor – it should take somewhere between 2-6 weeks to see a change.

If all this draws a blank, your vet can arrange for your horse to undergo skin sensitivity testing – he may need to be referred to a dermatology specialist to obtain this service. Skin testing will assess his response to certain grasses and other known irritants found in the environment.

If your horse responds positively to any of these tests, a course of desensitisation may be embarked upon, involving regular subcutaneous (under the skin) injections of a gradually increasing quantity of irritant.

However, desensitisation can take up to a year to yield results, so removing the source of the irritant is likely to work much more quickly and effectively.

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