Depends on whether he sweats a lot and if he keeps condition on him. The more hair he has the warmer he will be which will stop him losing weight. Rugs aren't as good as the horses own hair. I normally blanket clip my Dressage mare. She hates her back being cold and I find she goes much better with the heat on her back. I know I could just use a quarter sheet but I can't use it in competition. She's not a big sweater and I've only got an outdoor arena so she appreciates the bit of extra warmth.