A crucial part of providing animals for research is successful breeding. Still, in many mouse facilities breeding efficiency is complicated by problems with reproduction, such as pre-weaning pup mortality. Both single pups and the entire litter can be lost, with loss of entire litters having the most substantial influence on breeding efficiency. Although pup mortality is a relatively common problem, the underlying causes are poorly understood. Since dead mouse pups are often eaten by their mother, there is a widespread belief that the female actively kills them, and that leaving mothers undisturbed will prevent the mothers from killing their pups. Another common assumption is that it is normal for laboratory mice to lose their first litter due to the mother being inexperienced. However, the scientific support for these assumptions are insufficient. 

This presentation will provide information on pup mortality in laboratory mice based on scientific data from studies examining the cause of litter loss, and give recommendations on how pup mortality can be reduced. Use of the terms cannibalism and infanticide will also be discussed and the importance of finding the real cause of pup mortality instead of assuming why pups die will be stressed.