Producing mice for bioassays

Groups of breeding females were caged together for 3 weeks before putting them (1 or 2 per small box) with males, for 4-5 days. They were then pooled again until shortly before parturition. The majority of pups were born 22 or 23 days after pairing and were reared in foster litters, usually consisting of 27 pups with 3 foster mothers. Non-pregnant females and those not required as foster mothers were pooled once more. All pups were weaned on the same day, 19 or 20 days after birth, when all females were again mated. The average production rate was approximately 4 usable pup per female in the batch every 6 weeks. By maintaining 3 asynchronous batches of females a regular fortnightly supply of experimental animals was maintained with minimum wastage of food and labour.