Most males go off feed during the winter due to breeding season, if he has been with a female, that is where his mind is, most will not feed when around a female during this time of year.

If you keep him in for 4-5 days on then 4-5 days off he might feed for you, as it will give him a chance to settle back in. Our breeder males didn't eat when we gave them 2 days on then 2 off, but changed to 4 on 4 off and they feed every time, and still breed well.

If he looses weight try to move him to another room and keep him warm, and offer food at night. Most males will not have any problems during the winter being off feed, so let him do what he wants, as soon as spring hits hard he will be back on food no problem.
Good luck with the breeding season.