Check in the mane area for any sign of mites. They can look like tiny white, or red, or black dots. They are hard to see, but if you look close you can spot them. I think as a yearling he should be old enough to handle either permethrin or pyrethrin (sp?) sprays. Those are the same active ingredients as used in kitten and puppy sprays so they aught to be OK. If not mites or lice, then he may have a touch of fungal infection going on. There are sprays for that, and even some shampoos. Someone once told me that they cleared their heat rash up under their horses mane by putting a little Lysterine on a cotton ball and wiping it down. I'm not a vet, but I know of people that have tried these methods to clear up problem areas. I think first you need to determine just what the actual problem is and that may take a call to the vet. You don't want him to scrath himself into a scarred up mess, and he is obviously very uncomfortable if he is scratching that much. Good luck!