Q. My Arab mare has lumps on her body. When they first appear, a scab forms on top andthen they go down. She is itchy, especially under the saddle when I ride. My vet couldn’t make a diagnosis. He gave her granules in her feed, penicillin and three skin washes but none of these worked. Can you help?

Jo Holmes MRCVS replies: It sounds like your horse has an allergic reaction to something in her diet or environment.

Obviously your vet has tried treating her for ringworm and bacterial dermatitis without a positive result, so it seems an infectious agentis not the cause.

Firstly, cut out hard feed and see if this helps. It may take four to six weeks for the lumps to reduce but itchiness may improve within a few days. Modern feeds contain many ingredients, all of which can trigger an allergic reaction.

Identifying the exact component is hard, but avoiding certain brands may help. You can eliminate hay and bedding as the cause by turning her out all the time, but change one thing at a time.

If you can’t turn her out, try paper bedding and vacuum-packed or hydroponic grass.

If this fails, there may be a seasonal allergen such as pollen triggering this problem. To be sure, see if the condition improves as the seasons change.

If you want to find out before then, ask your vet if your horse can be skin tested for environmental allergens.

If a culprit can be found, you can start a programme of desensitisation, but this takes months and doesn’t always work.

Finally, don’t wash her numnah with a biological washing powder that she may react against.

Use only water to wash sweat off after riding. Don’t brush it off later as some horses end up with sweat lumps if they are not washed.