losing fur?

I have a young horse, he's about 5. He is from canada, he currently lives in florida. He has only been down here for 2 summers, this being his 2nd. He is a chesnut, who is losing his fur. His previous owners said he loses fur in the heat. Is there anyway I can get his fur to regrow thicker or where it won't fall out as much?

Is he losing his coat down to the skin or just to a thinner level of coat? Is it fairly consistent over his entire body or is the hair loss patchy? What is the condition of the skin beneath the areas of hair loss? Pictures would be helpful.....one person's idea of "bald" can vary quite a bit from someone else's.

My horse does something very similar every summer, and I just smear ointment on it every day till the hair comes back.

(His falls out in patches)

But I'm not sure what yours is could be anything from mange to sweet itch...