In my experience (I have been at this for a LONG TIME, LOL – I am old) itchy skin is almost always a gut issue. As I have faced this problem myself, I can and do empathize with all our itchy friends and what WE think are behavioral issues. Believe me, when your gut is inflamed normal behavior goes right out the window. I know this first hand. It becomes increasingly difficult to focus on anything other than being miserable, and it does not always show in an obvious way on the outside so we think things are OK. Not gonna show up on a blood report either usually. Sometimes allergy testing reveals issues, but if the gut was sound the allergies would not be there in the first place. Consider yourself lucky that this has not worsened to something like ulcers or colic. As another person already mentioned, Platinum Performance Skin and Allergy was used to some success, so I looked up the ingredients. Sure enough, Omega 3 DHA and Quercetin (an antihistamine), plus thymus extract to level out immune function. When the gut is irritated the body produces excess histamine and there is sometimes neutrophil “invasion” which releases proteases, a natural healing response to the irritation. This produces low level inflammation that becomes chronic in the gut unless something is done to break the cycle, and that is hard to do since our guys have to keep eating which sometimes keeps things irritated. (this is a simple explanation – it actually is quite complex) I have seen major improvements (although not totally fixed) in my worst horse (horrible food allergies, diarrhea, itching, hives, mouth sores and swelling, skin sores, hair loss, lamanitis since age 2 – he is now 15) by adding stabilized rice bran (about 1 1/2 cups a day), 1/2 cup ground flaxseed (I get the one from Triple Crown Feeds), 1/4 cup coconut oil (to help absorb the fats and other nutrients better which are needed and necessary for proper prostaglandin balance), and the amino acid L-Citrulline (3 grms daily), which blocks, to some degree, the neutrophil invasion and helps restore blood flow by increasing nitric oxide production. Additionally I make my own horse feed by using high quality alfalfa pellets as the base. Alfalfa has some antihistamine properties and high levels of vitamin K. Could this be why our horses usually crave it? Doing this does require some effort on my part to make sure they get the proper balance of nutrients. I add whey protein and gelatin (human grade) in a relatively small amount to boost amino acids naturally and help with tissue repair. Each of my boys gets an apple a day (quercetin) and 1 (medicinal, LOL!) peppermint candy which contains real peppermint oil and tumeric for the color. This stopped my colic prone horse from having tummy issues just like that. Peppermint oil is very powerful, and very little is usually needed. They also love Meadow Mints as a treat. My personal opinion is that most horse feeds just do not have the wholesome ingredients that we ultimately would like to feed our guys. I decided to stop feeding my horses what are often the “sweepings from the floor” of the feed mills, doctored up with inferior ingredients for palatability and low quality synthetic vitamins and amino acids, and sometimes harmful ingredients as preservatives. IMHO food sources for these nutrients are always best and provide a synergy that individualized nutrients lack. Others here mentioned turn out, and that can be critical if the horse can find in his pasture various forages that (believe me) they know they need. (Watch them go for the dandelions in the spring as a liver tonic.) These brilliant animals make every effort to get what their bodies tell them is needed. Unfortunately they cannot always get what they need in a domestic situation. So sometimes a high quality supplement might be necessary. They are all individual in what they need… and in my experience I have learned to watch and listen to what they do, what they eat, and what they don’t eat to gain clues as to how to better help them. Not trying to sound like a know-it-all, but having researched this for myself, (when doctors could not help me in spite of a diagnosis) I have been able to improve my two remaining horses’ quality of life by applying some of what helped me as well. We are not that different from our beloved companions. If something I have suggested here helps your guy or any other horse (or dog, person, cat…. or any pet) then I will sleep better knowing that one less is suffering from the misery of this common problem. All the best! Getting off the soapbox now, LOL!