Moncek et al. (2004) compared the stress response to gentle 1-minute handling of male Wistar rats kept in groups of three or four animals in barren cages with subjects from groups of ten animals living in five times larger cages that were enriched with various toys, tunnels, swings a running wheels. The large-group/enriched rats showed significantly lower ACTH, corticosterone and adrenaline response to handling than the small-group/nonenriched rats. It is not clear whether the stress buffering effect was exerted by the larger number of group members, the larger space available to each subject, the enrichment or, presumably a combination of these factors.

Belz et al. (2003) studied jugular vein-cannulated individually housed female Sprague-Dawley rats who lived in 1100 cm2 large cages that were either barren or enriched with rubber toys for gnawing and squares of compressed cotton fiber for shredding. The living space was the same for all animals, but those of enriched cages not only were easier to handle but they also showed a significantly lower endocrine [adrenocorticotropin] stress response to intraperitoneal injection. This effect could not be verified in male rats. Sharp et al. (2005) assessed cardiovascular stress responses to common handling procedures in SH rats bearing radiotelemety transmitters, who were individually housed in 930 cm2 large cages that were barren or enriched with a simulated burrow, a feeding enrichment gadget, and a shredding-and-nesting item. While blood pressure was not affected by enrichment, heart rate responses to subcutaneous injection and to tail vein injection were significantly lower in enriched versus non-enriched rats, indicating that enrichment had a stress buffering effect during these common procedures. This effect could not be replicated in Sprague-Dawley rats.