Australasian Science: Australia's authority on science since 1938

There’s More to Hen Health than Housing Style

By Stephen Luntz

A comparison of chicken stress levels has found that other factors are more important than whether they are housed in cages or allowed to roam free.

Dr Jeff Downing of the University of Sydney measured the levels of the stress hormone corticosterone in eggs laid by Isa brown hens between 24 and 72 weeks at 12 farms.

“When we combined the results of each housing system there were no statistical differences between corticosterone levels in cage, barn or free range hens,” Downing says.

Samples were taken from eggs because blood sample collection not only stresses the hen but also those around her. Downing has previously shown that levels of corticosterone in egg whites correlates with levels in the hen several hours before laying.

Downing says that corticosterone is used as the key indicator of stress in birds. “It acts as an energy mobiliser and also produces effects in the brain,” he says.

“In most of the farms, concentrations of corticosterone were higher in the earlier part of the production cycle, suggesting there are greater challenges for hens and potential for poor welfare at this time.” Downing thinks that as they became used to their environment hens often “learn to perceive challenges in a manner that doesn’t link to negative emotions”.

While the space in which hens could move did not show a significant difference in Downing’s study, some farms did much better than others. For example, factors such as temperature control appeared to be more important. Downing agrees that this provides challenges for consumers wanting eggs from happy hens, as this information is not widely available.

However, commercial pressures may still lead to better housing. “Cortico­sterone levels were significantly linked to egg production at the early stages,” Downing says. “They didn’t quite make significance levels over the whole cycle, but I suspect this is because we didn’t have enough data from all the farms.”

If the findings can be verified, producers may choose to please their hens to boost production.

Downing adds that it may be possible to pass legislation requiring farmers to meet some sort of schedule, or to monitor corticosterone levels on a regular basis, but such procedures will be more complex than banning small cages.