Globally, laboratory mice and rats are the most widely used research vertebrates. But for the >100 million rodents used in experiments each year, how their housing affects their welfare is often little considered. Conventional laboratory rodent housing in much of the world comprises small, barren cages containing nothing more than contact bedding, and even for the 10% or so kept under the higher standards of Canada and Europe, the only addition may be nesting materials. Such cages thus restrict exploration, exercise, hiding and burrowing (plus other natural activities) and effective thermoregulation.

This project will build on a previous systematic review by Cait and Mason that showed that mice and rats in conventional cages have increased all-cause mortality rates, shortened lives, and more severe morbidity in studies modelling five stress-sensitive diseases (anxiety, cancer, cardiovascular disease, depression and stroke). It aims to answer three further questions.

• Which resources do rats and mice need to be protected from chronic stress?
• Using body weight as a proxy, can abnormal behaviours flag the health impacts of conventional cages?
• Do research results differ in conventional versus well-resourced cages?

The findings of this study will be used to make recommendations on how best to refine rodent housing systems in ways that have the greatest impact on laboratory rodent welfare and may show that rodents housed in well-resourced environments increases the validity and applicability of their results to a greater portion of the human population.