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The implementation of Russell and Burch’s three R’s of Replacement, Reduction and Refinement led to a myriad of published literature on animal-friendly alternatives. But refinement as the one R that really has the potential to ameliorate the kept mice’s welfare is often neglected. In the field of refinement during the perinatal period till weaning, only few empirical investigations were performed. Postnatal litter loss reaches numbers between 0-50% and thus seems to be a neglected issue in laboratory mouse breeding. This gives reasonable cause for further investigation. Existing research recognizes the critical role played by the correlation between environmental enrichment of the breeding cage and maternal behaviour. The present study investigates the impact of different amounts
of environmental enrichment in breeding cages on infant survival rate and development. It especially attempts to reveal the conditions which are associated with high litter losses. To ensure a close monitoring, infants were counted daily. In addition, the infants were weighed on postnatal day three and postnatal day twenty-four. In impoverished breeding cages, with just soiled bedding material without any other enrichment, infant survival was significantly lower than in standard enriched breeding cages. Standard enriched breeding cages showed less divergence concerning infant survival rate compared to breeding cages with overstuffed environmental enrichment. A change to standard environment enrichment on postnatal day one did not prevent the infant losses. We hypothesize that the high infant losses may be caused by high peripartal stress of the dam. Peripartal stress due to poor environmental enrichment has a sustained negative impact on maternal behaviour. The subsequent implementation of the gained knowledge will be one further step to fulfilling the 3R-principle. It has the power to refine the dams’ wellbeing which consequently leads to a reduction of bred animals.