I used to breed year-round, but after a few years - actually quite a few years - I was doing a review of my records and I realized that most of my litter losses were in December and January. I didn't lose all the litters, just a much higher percentage than in any other month. Also at that time of year, hormones are at a low and the does are usually not at all interested, and it takes a lot of effort to convince them. So now, as a rule, I do not breed for kindling in those two months. By late January, though, the sunlight is increasing enough that the rabbits are usually raring to go, and I generally have my first litters arrive in February (which can actually be one of the coldest months here). My last litters for the year usually arrive in late October/early November (which is often another bitterly cold month).
It doesn't seem to be the cold, per se, that causes litter loss for me. I have had rabbits kindle at 15 below, and as long as the kits are tucked into that fabulous fur nest and fed well by the dam, they do fine. The real problem, I believe, is what I alluded to above: the does are not hormonally prepared to raise babies at that time of year. Even with a lighted barn, low winter hormone levels mean the does don't have all their instincts firing at full strength. Even experienced does will have babies on the wire, or not cover them up, or sit in the box, which causes the babies to come up to the front to try to nurse and when the doe doesn't want to feed them and jumps out, she takes some of them with her. Litters tend to be smaller, which presents a problem if there aren't enough to keep each other warm. Finally, I don't have actual data to back this up, but I think does' milk production also drops, which means the babies aren't fully fed, so they crawl up to the front of the box looking for food, which results in scattering the litter or babies popping out of the box; in either case, they freeze.
Taking this all together, and really hating to find "bunnycicles" all over the wire, I decided not to fight it and just roll with a 2-month break. I don't really miss butchering in the freezing cold; the only issue I have is that the does do tend to get fat during their hiatus, and I have to be very vigilant about feeding them enough to keep them in condition but not get so fat that they have trouble conceiving and/or kindling. This is a major problem for me with does two years old or older. (I have young helpers who are not always precise about measuring feed!)
My barn is a custom-built 20th anniversary gift (at least I think of it that way!) built by my husband after 16 years of jury-rigging my rabbit area, so it is my dream barn.
It is a 20' x 24' pole barn with a dirt floor, a metal roof and 1-1/2" thick styrofoam board (the kind that is white on one side and silver on the other) packed in between the rafters. The sides/doors are not insulated, there is a gap of maybe 6' between the top of the walls and the roof for ventilation, and the doors are regular swinging barn doors, not at all "tight," so there is plenty of airflow. With about 32 holes (nearly always full - rabbit math!), the barn stays about 10 degrees F warmer than the outside air in the winter. Sometimes when the wind is howling, it drops to within 5-7 degrees of ambient, but the barn is protected on the windward side by a solid wall, and an open stable attached to it along that side, so it doesn't lose too much to the wind. (And happily, even though the windows and door are south-facing, it stays 10-20 degrees F cooler in the summer as long as we keep the door closed!)
