Brown and white layer pullet hybrids show different fear responses towards humans, but what role does light during incubation play in that?

Early-life conditions are increasingly recognized as essential to animal welfare later in life. Light during incubation is being investigated as a method to improve welfare in later life in poultry. It approximates more closely chicken natural environment before hatching, compared to the current conventional incubation
conditions in darkness. Previous studies were promising: lighted incubation resulted in more species-relevant behavior and lower stress reactions to various stressors after hatching. Most research, however, has
been conducted on broilers, and little information on lighted incubation is available for laying hens. In addition, white hybrids have been shown to be flightier than brown hybrids. In the current experiment, Dekalb
White and ISA Brown eggs were incubated in complete darkness or in a cycle of green 12L:12D throughout incubation. Five different human fear tests were performed on 387 chickens during the rearing phase. We expected dark-incubated chickens to show more fear and higher corticosterone levels than light-incubated chickens. The voluntary approach test matched this hypothesis, as the dark-incubated chickens froze more than the light-incubated chickens (pbetween the incubation treatments. In addition, we expected white chickens to show more fear and higher corticosterone levels than brown chickens. Four of the five tests (p≤0.002) confirmed that hypothesis. In the tonic immobility test, though, brown chickens showed more fear than white chickens. Finally, we expected light during incubation to have stronger effects on white chickens than on brown chickens, because
of the better transmission of light through white eggshells. However, the interaction between hybrid and incubation was never significant (p≥0.18). To conclude, this experiment did not show clear evidence that
light during incubation could improve laying hen welfare. Hybrids show differences in fear-related tests, and that should be taken into account in research and in laying hen management.