With summer ending, it would be a good time to worm him. Valbazen dosage is 1/2 ml orally, then repeated in 10 days. With chickens it's nest to stick with a good all flock food for roosters for at least 90% of their diet since it contains all of the vitamins, minerals, and balanced nutrients...
How old is he? You may try worming him with Valbazen or SafeGuard liquid goat wormer. If he is still pretty young, he may have coccidiosis, and Corid will treat that.