My OTTB gelding for some reason has a very dull coat in spots. His neck and shoulders, are shiny but from there back is not. It’s very dull and the hair in the saddle area is a lighter color than the rest of him, he’s chestnut. He’s up to date on vax and deworming and is eating 50/50 grass alfalfa plus a pelleted feed that contains alfalfa, beet pulp, rice bran, and flax, no grain. My other horses on the same diet have beautiful coats and dappling but not my guy. The vet suggested adding a vitamin/mineral supplement and extra flax, which I did but this is just a few days ago.
Any suggestions or ideas on why his coat would be so dull?