Metabolic cages

Metabolic cages create both welfare and scientific challenges and their use should be limited to procedures which are strictly necessary. Kalliokoski et al. (2013) concluded that mice do not habituate to metabolic cages.

Access to shelter in mouse metabolic cages

Introduction

An elevated level of albumin in the urine is a result of leakage across the kidney barrier and the use of 24h urine collection to calculate albumin leakage into the urine is an established measurement of kidney injury in rodent models. The time spent in the metabolic cages for urine collection is stressful for the animals. The animals are single housed with limited space, without a shelter on grid flooring and without bedding and environmental enrichment in the metabolic cage. Weight loss, lowering of the body temperature and ruffled fur coat can be seen in mice after metabolic caging. Prolonged stress is generally acknowledged to affect factors like kidney function and pharmacokinetics, so reducing stress in caged animals would likely result in more reliable research data.

Description of a mitigating initiative

In an attempt to reduce the stress, a small plastic igloo shelter was placed in the metabolic cages close to the water bottle. Mice can seek shelter in the igloo, thus reducing the stress and heat loss from single housing on grid floors. The rounded shape of the igloos prevents the mice from climbing the shelter and urine and faeces from accumulating on the roof.

Results

When using DBA2 mice, the mice lost on average 4.3% of their body weight in the week after caging, without the shelter. In the study using shelters the average weight loss was 1.4%.