Seasonal raised swellings on the neck are possibly hives. We have a paint gelding that is hypersensitive to insect bites and is prone to hives in spring and summer. We have found success reducing his symptoms by keeping him on ground flaxseed, such as Omega HorseShine, as well as using a fly sheet with an attached neck cover to help prevent the bites that trigger the hives. We like the fly sheets infused with insect repellent and use the Amigo Bug Buster, but there are several other options out there. We also will bathe him with a skin calming shampoo such as Absorbine Medicated Shampoo or Eqyss Micro Tek. The cold water and soothing ingredients help reduce the swelling and help him feel more comfortable. Another mare at our barn gets hives from certain fly sprays, so that is a possible irritant as well. Here’s an article from the SmartPak vet for more in-depth info: http://blog.smartpakequine.com/2012/10/how-do-i-get-rid-of-these-nasty-hives-on-my-horse/
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