Rats are the most widely used research animals after mice, with complex social and cognitive needs that standard laboratory housing routinely fails to meet.
Rat welfare in laboratory settings is significantly compromised by social isolation — the standard housing of single rats is a welfare failure recognized in growing regulatory guidance but inconsistently implemented. Rats housed alone show higher stress hormones, more abnormal behavior, and different experimental responses than socially housed animals — making isolation both a welfare problem and a scientific problem. Pair or group housing with appropriate enrichment is feasible and improves both welfare and data quality.