I appreciate all the input you guys posted. There is actually no hair loss there. He was clipped a few months so it might be in the picture his thin coat looks like there is a lack of hair? Our mare who lives in the same paddock as him, doesn't have them, so it's a very good suggestion that he might be more sensitive to something. Birdcatchers sounded like it could be it, but after reading about it, his spots seem much smaller than what birdcatchers spots come up as.
They both get bathed in bug spray as is, but maybe it's time to consider an alternate route because if its bug causing this to him, I need to do something else! Thanks so much for all the input so far everyone. Some really great suggestions.