Some does seem to do better than others when raising a litter, I usually free feed my does until the kits are weaned but you can get does who don't seem to be able to keep their condition. My blue Rex seem to stay fat no matter how big a litter they raise, but my dalmatians seem to struggle to keep the weight on while raising a litter. I offer oats, frutti mix feed, and herb grass which usually helps. You can also switch to higher protein feed and better hay but you need to do this over time obviously. If you get a doe that loses condition on every litter I would retire her early, some does are just not cut out to be mothers from my experience.