Poultry scientists examine laying hen welfare during depopulation in noncage systems - Interpretive Summary

Poultry producers maintain healthy, productive flocks by carrying out depopulation when hens reach 65 to 90 weeks old. Depopulation means hens need to be caught, carried and put in crates on their way to slaughter. The challenge is that hens in commercial systems are not used to being handled, and they often struggle to avoid being caught. As a result, each step of the depopulation process comes with a risk of injury and stress for the birds.

Researchers at the University of Bern are taking a closer look at how often hens show signs of injury and stress during depopulation. Their work could shed light on how to improve hen well-being, even at the end of the production process.

In a new study, published recently in the Journal of Applied Poultry Research^®, the researchers report that depopulation in multitiered aviary systems leads to severe injuries or stress in 8.1 percent of birds. This finding is lower than the 24 percent injury rate reported in some past studies and suggests that new ways of assessing hen welfare could allow scientists to better track hen welfare in different housing systems.

“A better understanding of the different insults to welfare as a result of the depopulation process and further information on the potential causes are necessary to effectively improve animal welfare,” write the study authors.

The new study was carried out on 15 farms, and the researchers assessed fractures, muscle damage, corticosterone levels and other signs of stress in 603 individual end-of-lay hens. To establish the effects of depopulation, the assessments were carried out before and during depopulation.

This was the first study of its kind in a noncage system. All hens came from multitiered aviary systems, with the exception of a small number from a single-tiered system. As the researchers point out, these noncage aviary systems are very common in Switzerland and are growing in popularity around the world.

In addition to the housing system, the researchers investigated how the hen “catchers” behaved during the depopulation process. They asked the catchers to share information on their experience, qualifications and “physical condition.” Catchers were also asked to wear a head-mounted camera to record the process.

The results were surprising. The researchers found recent fractures in 8.1 percent of the hens—but not from the sources they expected.

“Various elements such as feeders, drinkers, or perches can get in the way when catching hens. Based on recordings from head cameras, collisions did occur, although predominantly involving the wings and not the bones, where most fractures were identified, that is, the sternum, pubis, and furcula. More so, although we did not quantify impact energy, the collisions recorded by the head cameras seemed to be relatively minor,” the researchers write.

The researchers hypothesize that some of the fractures may be a result of diseases that have already weakened the bones in these hens. Hen handling may also be a factor. Some of the catchers attempted to crate several bundles of hens at once, and this technique could lead to fractures when hens collided with the metal openings of the crates.

“Further research should consider the crating and carrying process in greater detail to better understand the source of bone injuries and potential risk factors such as quality of lighting, the aviary system, or time of day that might influence handling of hens,” write the study authors.

When it came to stress, the researchers did see higher plasma corticosterone concentrations following depopulation. They did not see an overall increase in fear responses. There was an exception though—the researchers note that signs of fear increased in hens later in the depopulation process. This makes sense in the noncage system, as the hens caught last are the ones who spent the most time escaping the catchers.

The full paper, titled “Examining the catching, carrying, and crating process during depopulation of end-of-lay hens,” can be found in Journal of Applied Poultry Research and online here.

DOI: 10.1016/j.japr.2020.100115