to me the problem is more that its not light enough for them to eat enough to grow enough (if you see what I mean)in the depths of winter. And I wouldn't put growers outside without heat before at least 6 weeks that time of year-as well as give them a lot of shelter from wind and rain. So people do do it, but rear them indoors with heat and lights. I only breed purebreds now and am just doing my latest hatch ever-due next week, conversely I don't hatch before late March/April as the weather is just too crap to put them out earlier than 6 weeks when they are feathered up. I need them to be a good size to cope with winter weather (I am on an exposed site in Lanarkshire).