Stressed laying hens: TUM researchers clarify the genetic basis of chicken behavioral abnormalities

Feather pecking is not uncommon in laying hens in species-appropriate group housing: The animals pluck each other's feathers, some of these behavioral problems leads to cannibalism and death in the henhouse. In contrast, only the preventive pruning of the beaks helped so far. Now researchers from the Technical University of Munich (TUM) have found out why certain chickens are more prone to feather picking than others. With this knowledge, one could avoid torments in the laying hens in the future.

The end of chicken cage husbandry demanded by behavioral researchers and animal rights activists is finally becoming a reality: The cage ban will finally come into force on January 1, 2009. In Germany, therefore, the last laying batteries have to close and the egg producers have to switch to appropriate chicken farming. Here, laying hens are allowed to live in groups, maintain innate behavior such as pawing and sleeping on perches and lay their eggs in nests undisturbed. However, what is optimal for the animal in itself has a serious disadvantage: it is precisely in this animal-friendly attitude that so-called "feather pecking" can occur.

With this behavioral problem, chickens pluck each other's tail or body feathers - sometimes until an animal is barely feathered. In extreme cases, laying hens with behavioral problems even peck each other dead. Researchers have so far only been able to speculate as to why. Prof. Ruedi Fries from the Chair of Animal Breeding at the Weihenstephan Science Center at TUM has now brought light into the dark with his team - with the help of a behavioral biology experiment and subsequent gene sequencing.

Feather pecking is interpreted by some behavior researchers as an aspect of exploration behavior. By observing behavior on newly hatched chicks, the TUM researchers first showed that there are different "chicken personalities": The chicks of a line that lays white eggs explored their surroundings curiously in the experiment. As laying hens, they pecked only rarely and tenderly later. The animals of a comparison line that lays brown eggs remained cuddled much closer together as chicks. In adulthood, however, you show pronounced feather pecking.

By chance, Ruedi Fries came to the aid of the search for the reason: "I read a newspaper article about the personality of blue and great tits. For them, the variation of a gene called DRD4 was responsible for a different level of curiosity. " Fries concluded: If exploratory behavior has to do with feather pecking, the DRD4 could also be behind it in chickens. To investigate this, the researchers selected a total of five chicken lines: two breeding lines each from commercial chicken breeding and from a breeding experiment in which strong and rare feather pecking was selected, and a control group.

Fries' team used gene sequencing to check a total of 141 genetic samples from the various breeding lines for differences and similarities. The focus was on the "suspected" gene DRD4, which plays a role in the exploration behavior of titmice, as well as the neighboring DEAF1. This gene is associated with the development of depression. The researchers found two things they found: In both genes, they discovered a significant connection between the gene variant and the tendency to feather pecking, both in the commercial chicken breeds and in the others.

The gene variants seem to decisively determine the condition of the chicken. Hens who tend to peck feathers are apparently latently depressed and quickly stressed due to their genetic makeup. "Further studies have yet to confirm this," says TUM geneticist Ruedi Fries. The project's industrial partner, a world-leading chicken breeder, has already applied for a patent for the results: He wants to use the knowledge to specifically develop lines that are not prone to feather pecking - and are therefore particularly suitable for animal-friendly husbandry.

"The results are very interesting for a second reason," said Prof. Fries. "Genetic behavioral research in birds can also fertilize research into mental illnesses." Maybe chickens will help us to understand depression in humans better in a few years - and eventually to treat it more effectively.

Source: Munich [TUM]