The effect of light during incubation and dark shelter enrichment on chick growth and behavior

Early-life conditions can influence chick development and welfare. In this study, we investigated the effect of light exposure during incubation, and a post-hatch dark shelter enrichment, on layer chick growth and behavior. White Leghorn chicken eggs were incubated under either full-spectrum white light (24L:0D) or darkness (0L:24D) in temperature-compensated photoperiodic boxes. After hatching, chicks were reared in either standard pens or pens with a dark shelter enrichment. The study was conducted using four cohorts of chicks, resulting in eight replicates per treatment combination. All cohorts were used to assess chick growth; three cohorts were used to measure behavioral time budgets and interaction with the dark shelter, and the final cohort was used to examine behavior while inside the dark shelter. Chick behavioral time budgets and dark shelter use was continuously recorded via video over four weeks and quantified. Hatching success was not affected by light during incubation but there were age- and sex-specific effects on body weight by four weeks, female chicks incubated under light, tended to be heavier than those incubated under dark conditions. The dark shelter enrichment reduced overall chick activity and foraging while increasing resting behavior, with effects dependent on incubation treatment and age. In response to enrichment, light-incubated chicks showed decreased activity and foraging, and increased resting, compared to dark-incubated chicks. In contrast, in standard pens, light-incubated chicks were more active and foraged more than dark-incubated chicks. Our novel findings show that light exposure during incubation shapes early-life behavior in layer chicks and modulates their responses to dark shelter enrichment. Further research is required to determine whether lighted incubation and post-hatch dark shelter enrichment improve layer pullet long-term welfare.