Health Monitoring of Laboratory Rodent Colonies—Talking about (R)evolution

SIMPLE SUMMARY: When working with laboratory animals, scientists need to ensure that animals are not suffering from natural infections. Therefore, hygienic standards have been developed over the last 100+ years. The key element of hygienic standardization is the monitoring of infectious agents that can compromise the animal’s health, are dangerous for the personnel or interfere with the research. However, scientists became aware that by eliminating such unwanted infectious agents the overall diversity of all microbes in research animals, the so-called microbiome, has also been reduced. Moreover, it became clear that the microbiome composition has an enormous impact on how research models react, e.g., to treatments. This might hinder the translation of findings in preclinical research to the clinical situation. Therefore, new concepts in hygienic standardization need to be developed that take animal welfare as well as scientific value into account. In this review, we will give an overview of how classical monitoring has been evolved and demonstrate concepts regarding how to handle the microbiome as a yet unknown variable in animal-based research in order to enhance the validity of research findings. ABSTRACT: The health monitoring of laboratory rodents is essential for ensuring animal health and standardization in biomedical research. Progress in housing, gnotobiotic derivation, and hygienic monitoring programs led to enormous improvement of the microbiological quality of laboratory animals. While traditional health monitoring and pathogen detection methods still serve as powerful tools for the diagnostics of common animal diseases, molecular methods develop rapidly and not only improve test sensitivities but also allow high throughput analyses of various sample types. Concurrently, to the progress in pathogen detection and elimination, the research community becomes increasingly aware of the striking influence of microbiome compositions in laboratory animals, affecting disease phenotypes and the scientific value of research data. As repeated re-derivation cycles and strict barrier husbandry of laboratory rodents resulted in a limited diversity of the animals’ gut microbiome, future monitoring approaches will have to reform—aiming at enhancing the validity of animal experiments. This review will recapitulate common health monitoring concepts and, moreover, outline strategies and measures on coping with microbiome variation in order to increase reproducibility, replicability and generalizability.