A single gene makes the chicken a victim

Feather pecking is a common and serious behavioural disorder in laying hens around the world. The chickens peck and pull the feathers of their victims, and this may lead to cannibalism. Now a group of researchers under the lead of Per Jensen, Professor of ethology at Linköping University have shown that the risk of becoming a victim is largely determined by one single gene, which controls the expression of black pigment in the carrier. A mutation which gives white feathers protects against the attacks. The research is published in this week’s Nature.

Per Jensen and his group has, together with Professor Leif Andersson’s group at Uppsala university, for several years mapped genes for different behaviours in poultry. By crossing jungle fowl (the ancestor of all domestic fowl) and laying hens, they have hatched more than 1000 individuals whose DNA has been analysed with the help of genetic markers at the same time as a range of different behaviours have been studied and quantified for each individual. When Jensen and his co-workers studied feather pecking, they also recorded the plumage condition on all birds – a feather pecked chicken becomes nude on large parts of the body.

The plumage condition proved to be strongly dependent on the genotype on one particular position of chromosome 28. Right there the gene, which was found to be decisive for the fate of the carrier, is situated. The gene is called PMEL17 and controls the expression of melanin, which gives black pigment. A mutation, which leads to white feathers, provides the carrier with a relatively good protection against becoming a victim.

Feather pecking is an example of a relatively common behavioural disorder in animals kept under intensive farming conditions. This is the first time that it has been demonstrated that the appearance and genotype of the victim is important for the development of such a disorder. The mechanism behind this, and the extent to which similar aspects are relevant in other species as well, remain to be investigated.