Bucks should never be in with does and litters. Rabbits can be very territorial. A buck can also rebreed the doe before she has even weaned the present litter and breeding back t back like this can be VERY stressing on the doe. The female could kill her litter out of instinct or refuse to care for them. The male could kill the kits (territory) or cause serious injury to them. The female could attack and seriously injure the male or get injured herself when he fights back. I have seen some pretty nasty injuries caused by territorial rabbits and have always be careful with mine – especially when I was actively breeding and had unaltered bucks and does. (My husband was scarred by a very territorial unneutered buck. The buck was a show prospect being sold – i had too many solid show potential buns from this litter and could not keep them all). He was fine as long as you did not smell of another rabbit strongly. We were at a fair with him, my husband had shown another rabbit prior to him and now was going into his cage to chage water, the buck got very territorial with the other rabbits around him and nailed my husband badly. He was an adolescent and placed as a pet with a neuter agreement and insistance that he be a single rabbit only. He went to a little girl whom he adored. He just was a territorial bun and could not be near other rabbits. This behavior was not seen in any of his littermates… It is never a good idea to leave a buck in with a doe who is pregnant and has a litter with her. Actually, she should have a cage to herself the entire time. Though rabbits can bond pairs, those in bonded pairs should be spayed or neutered. Hormones affect behaviors (rabbits still have many wild instincts) and those that are not spayed or neutered are often more territorial than those that are.