Believe me there's a difference between looking hogged & hogged, particularly when it comes to growing it out! Trim the rest, it'll still be obvious but not as much so as if the rest is long - do we have a shot of the mane side? - & gently massage the chewed out areas with something soothing to ease any soreness & also encourage growth. The fact that he hates anything being put on it makes me wonder if the skin is irritated or sore so maybe something like aloe vera gel would help while massaging will improve blood supply & stimulate growth. Maybe something like a strong smelling, and therefore hopefully tasting, fly gel either side of his crest but not actually on the mane area would put off whoever is chewing him?