Hi. My ISH has this issue. I tried allergy shots to desensitize him to really no avail. My vet advised that he thinks it is related to a type of insect called a midge. It is not uncommon in horses. I do have it under control after vet consults and many years. Here is my regimen: Wash with T-gel or generic type of shampoo that is tar based. DAILY fly spray affected areas – the whole horse actually but especially where he itches. ENDURE is the recommended one. EVERY DAY. one bite and he will itch. My horse also got sores on his legs from itching. Now he goes out at 7:30 AM and comes in at 12/1 PM. He is also a nonsweater. In addition I used Prednisolone for severe outbreaks and he is on a maintenance dose of 5 a day or every other day during the bad summer months.
No quick fix on this one.