How the Micro-Environment Can Improve Mouse Breeding Success
Breeding healthy laboratory animals is a crucial aspect of scientific research, yet it is often overlooked in discussions about animal welfare and research numbers. High pre-weaning mortality rates among laboratory mice pose a significant challenge, with up to 1.4 million mice estimated to die annually before weaning. This not only impacts animal welfare but also has broader implications for scientific, economic, logistic, and sustainability considerations.
Recent studies have identified various factors that can influence pre-weaning mortality rates in laboratory mouse breeding. These include micro-environmental factors such as cage temperature, light intensity, cage enrichment, bedding material, and animal-related factors like dam handling and parity. Litter overlap, a common occurrence in breeding facilities where males and females cohabit, has been identified as a major driver of increased pup mortality. When new pups are born in the presence of older pups in the cage, the risk of mortality significantly increases.
In a comprehensive study involving 509 litters of C57BL/6J mice, researchers found that overall pup pre-weaning mortality was 25.6%. Death of the entire litter occurred in 19.1% of litters, with most deaths occurring within the first 24-48 hours post-partum. Factors such as dam age, litter overlap, the number and age of older pups in the cage, and the size of the focal litter all influenced pup survival rates. Cage micro-environmental factors, including cage temperature, light intensity, vibration, motion events, and nest score, also played a role in determining pup mortality.
By analyzing the data collected from the study, researchers were able to identify key risk factors for pup mortality and develop strategies to improve breeding success. The findings suggest that optimizing the micro-environment of breeding cages, providing appropriate nesting material, and reducing litter overlap can help reduce pre-weaning mortality rates in laboratory mouse breeding operations.
In conclusion, understanding and addressing the factors that contribute to pre-weaning mortality in laboratory mice is essential for improving breeding success and ensuring the welfare of research animals. By focusing on the micro-environmental conditions and social factors that impact pup survival, researchers can work towards reducing mortality rates and promoting more sustainable and ethical practices in animal research.
References:
• European Commission. Summary Report on the Statistics on the Use of Animals for Scientific Purposes in the Member States of the European Union and Norway in 2019.
• Gaskill, B. N. et al. Energy reallocation to breeding performance through improved nest building in laboratory mice.
• Weber, E. M. et al. Influence of strain and parity on the risk of litter loss in laboratory mice.
• Morello, G. M. et al. High laboratory mouse pre-weaning mortality associated with litter overlap, advanced dam age, small and large litters.
The study highlights the importance of considering the micro-environmental factors in laboratory animal breeding to improve breeding success and reduce pre-weaning mortality rates. Through targeted interventions and adjustments to the breeding environment, researchers can work towards enhancing animal welfare and scientific outcomes in laboratory mouse breeding operations.