Can Early Environmental Enrichment Buffer Stress from Commercial Hatchery Processing in Laying Hens?

Abstract

Under commercial conditions, laying hen chicks are exposed to a range of stressful events immediately after hatch. Here, we studied whether environmental enrichment was able to reduce the stress sensitivity of these chicks. A total of 50 hatchery chicks (HC) and 50 control chicks (CC) were raised in enriched pens (E), while 53 HC + 53 CC were raised in standard non-enriched floor pens (NE). HC weighed less on day one, but there was no effect of hatchery treatment at later ages. HC were more pessimistic in a cognitive judgement bias test and emitted more distress calls when socially isolated, indicating that hatchery stress affected behaviour and stress sensitivity. However, enrichment did not affect the behaviour in any of these tests. We found no effects of hatchery stress in a novel environment, but indications that enrichment may have increased fearfulness of HC. The sensitivity of the hypothalamic-pituitary-adrenal (HPA) axis was reduced in HC-E compared to HC-NE, indicating that enrichment buffered the physiological stress sensitivity in HC; however, the opposite pattern was found in CC. In conclusion, our results show complex and somewhat contradictory effects on the ability of enrichment to buffer the consequences of stress in commercial hatcheries.