is she ok

Question
hi again.
our rabbits have a pretty  strange story. on the 15 of dec my sister had found one of our bunies had died.a few weeks before that we had found a large rabbit in our vegtable garden, he was tame so we kept him.(we hadn't yet found out that it was a boy)after a week we put them all together in the large avery.(we have 2 females). after we found the dead rabbit, my sister found a nest of babies under the straw, we assumed that they were from the dead bunny. but then we figured that they wouldn't still be alive(this is 2 days later) and the other female had milky teats. so we put them all together in a smaller avery seperate from the dad. all was fine. 2 weeks later i found another litter... so it turns out that this small little dwarf bunny adopted the 1st litter and then brought up her own. she hasn't really put on weight and is no longer breast-feeding. we feed them lettuce, fresh spinach and pellets... is there anything else that we can give her???
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-----Question-----
how old must male rabbits be when seperated?? the litter was born on 15 dec and we have split them already, but need the avery space for a new litter. Any help would be great, the male rabbit is in a different avery next to the others with birds... is that ok??
-----Answer-----
That would make them about 8 weeks old, correct? If so, you will probably be safe keeping them together for another couple of weeks, but keep an eye out for any signs of fighting.

I'd really not recommend keeping rabbits with birds, though, as it is possible for some diseases and parasites to transfer between the two species.

Answer
Make sure the lettuce you are feeding is not iceburg lettuce. It contains pretty much no nutrients. Instead, feed dark green lettuces like romain and bib lettuce.

You can get Calf Manna from most feed stores. This is great for putting weight back onto a rabbit, and most rabbits love it.