Neonatal animal models are increasingly employed in order to unravel age-specific disease mechanisms. Appropriate tools objectifying the clinical condition of murine neonates are lacking. In this study, we tested a scoring system specifically designed for newborn mice that relies on clinical observation and examination. Both, in a neonatal sepsis model and an endotoxic shock model, the scoring results strongly correlated with disease-induced death rates. Full as well as observation-restricted scoring, reliably predicted fatality and the remaining time until death. Clinical scores even proved as more sensitive biomarker than 6 traditionally used plasma cytokine levels in detecting sepsis at an early disease stage. In conclusion, we propose a simple scoring system that detects health impairments of newborn mice in a non-invasive longitudinal and highly sensitive manner. Its usage will help to meet animal welfare requirements and might improve the understanding of neonatal disease mechanisms.

Newborn individuals are highly susceptible to infectious diseases. For better insights into age-specific host-pathogen interactions infection models are increasingly employed in neonatal mice. However, for newborn mice no measures are available to objectify the clinical disease state, particularly not in a longitudinal manner, to meet legal animal welfare requirements. We developed a scoring system for newborn mice that relies on observational and examination-based parameters and validated it by applying a Staphylococcus aureus-induced infection model in two different mouse strains.The scoring results strongly correlated with the death kinetics independent of which mouse strain was used. A score above 7 predicted fatality. While the score values increased already at early sepsis stages the large majority of plasma cytokine levels remained comparable to those in uninfected control neonates. The levels of interleukin (Il)-6, chemokine C-C motif ligand 5, Il-1α and tumor necrosis factor α were not increased before 24 hours after infection and correlated only at this late stage of sepsis with the scored disease state.We propose the first clinical scoring system that serves as important research tool to evaluate the clinical course of sepsis in newborn mice. It detects health impairments of newborn pups in a highly sensitive and longitudinal manner, providing information about the disease severity as well as prognosis.