Early death of mouse pups is a commonly known problem in breeding mice colonies, which is still often regarded as 'normal' or is even overlooked due to the counting procedures applied. As reduced breeding performance probably indicates reduced well-being, this seems to be an underestimated welfare issue in laboratory mouse breeding. The present study compares the influence of three different forms of enrichment in breeding cages on infant survival rate and development of C57BL/6J mice. Our data reveal that lack of enrichment results in greater preweaning pup mortality, reduced weight and delayed development. Changing the environmental conditions after birth cannot prevent litter loss but improves the development of pups born in impoverished environments. Overall, our results underline the importance of early counting of mice for optimizing refinement strategies to ensure well-being and breeding success.
Keywords: 3R; breeding; environmental enrichment; pup mortality; refinement.