Spring and fall most of my larger breeds bred back to back. Weaned at 4weeks and had the next litter. They stopped for the hottest month or 2 with the bucks often going sterile anyway and most I didn't breed for several months over winter. Except a few like the creme d'argent who would tear down dividers to get to bucks and build nests that could raise kits in subzero. Some breeds didn't handle a heavier breeding schedule such as Netherlands and might take a month or 2 to recover condition if they had 2 close litters.
