Light study offers insights on chick development

Exposing eggs to light while they develop leads to chicks engaging more with environmental enrichments after they hatch, a new study has shown.

Researchers found that chicks incubated in light were more likely to use shelters in their environment than chicks that developed in darkness.

Understanding how early-life conditions shape behaviour could help inform practices that improve welfare across the egg and poultry sector. 

Scientists at the Roslin Institute studied groups of eggs incubated under different conditions. Some eggs were kept in darkness, while others were exposed to light. After hatching, some of the chicks were given access to a small, dark shelter in their pen, while others were not. The researchers then observed how the chicks behaved in the days and weeks following hatching.

The study found that all chicks made use of sheltered spaces to rest within or against, and to perch upon. Chicks that had been exposed to light while in the egg, by comparison, interacted with the shelter more often than those incubated in darkness.

Sheltered, dark and warm spaces are thought to mimic maternal care in the first days and weeks of life, reducing stress and unwanted behaviours, like injurious pecking, the team suggests.

Overall, chicks provided with a shelter were less active and rested more. As the grew older, they increasingly engaged with the shelter, mostly using it to rest inside, as well as resting against it or perching upon it. 

In commercial poultry production, eggs are usually incubated in darkness. In contrast, eggs incubated naturally by a hen are exposed to daylight when she leaves the nest.

The findings suggest that light exposure during incubation may provide benefits for chicks after hatching. Previous research has shown that light during incubation can improve hatching success, support growth, reduce stress, and influence brain development.

The study adds to growing evidence that simple environmental enrichments, such as shelters, can improve chick welfare by offering places to rest, perch, and take breaks away from other chicks. 

Females that were incubated in light conditions weighed more by four weeks of age, compared with females incubated under darkness, which could have implications for productivity in egg-laying systems.

Light exposure did not affect when individual chicks hatched. However, the researchers suggest that regular light–dark cycles during incubation could help synchronise hatching across a clutch. This is because birds have light-sensitive receptors deep in their brains that help regulate daily rhythms, that are responsive to light signals even before hatching.

The research, published in Poultry Science, was carried out with the National Avian Research Facility and supported by the Animal Welfare Foundation, UKRI Biotechnology and Biological Sciences Research Council and EastBio Doctoral Training Partnership.