In this Review, the authors provide recommendations for the implementation of the 3Rs in all the steps and procedures in the generation of genetically modified rodents; they also discuss future welfare challenges associated with advances in genome modification techniques.

This protocol describes a humanized mouse model created using neonatal thymus and umbilical cord blood hematopoietic stem cells as nonfetal human tissue sources.

A large number of refinements have been studied with the aim to improve rat welfare, but more evidence is needed to fully understand their impact. This mapping review draws on the findings of 1,017 studies to show that different refinements impact different rats in different ways, and that a ‘one-size-fits-all’ approach to refinements might not be appropriate.

Unpredictable chronic stress (UCS) increases anxiety/fear-related behavior and cortisol levels while decreasing locomotor performance, according to a systematic analysis of 38 studies on UCS in zebrafish. To further assess the effects of UCS on zebrafish behavior, future well-designed trials are required.

Two Cre-dependent reporter mice, oFluc and Akaluc, were created and tested for bioluminescence in neural tissues and organs. Both strains were brighter than the classical luciferase Luc2, potentially facilitating in vivo bioluminescence imaging of various tissues.

The authors developed an R package that enables the estimation of group size required for mouse breeding, taking into account Mendelian genetics, fertility and litter size.

This protocol describes a humanized mouse model created using neonatal thymus and umbilical cord blood hematopoietic stem cells as nonfetal human tissue sources.

The authors investigated the influence of housing density and bedding volume on ammonia build-up in two individually ventilated mouse cages models. While the amount of bedding had no influence on ammonia levels, smaller Type II individually ventilated cages accumulated higher ammonia levels than larger Type III individually ventilated cages, even at similar housing densities.

A mouse model to study norovirus pathogenesis is described. The murine norovirus strain WU23, originally isolated from an intestinal site, induces severe but self-resolving diarrhea in neonates, reflecting the pathology observed during human norovirus infection.