DNA region in chickens identified for disease resistance

Researchers from Wageningen University and Hendrix Genetics found that 1 region in the DNA of a chicken explains a large difference in possible disease resistance between birds.

This DNA region contains, among others, an important sensor for activating the immune system, which might explain why some chickens become ill and others do not.

Pathogens can easily spread through poultry housing systems and the reduction of use of antibiotics and the move to group housing of layer chickens has increased the need for a more robust layer chicken. In previous research, scientists found that birds have natural antibodies, which inhibit and prevent further infection in the body, but also warn and activate other parts of the immune system. Earlier studies have shown higher natural antibody (Nab) levels in layers that were associated to an increase chance of survival, and levels are heritable and thus can be influenced by breeding.

Identification of DNA region

To get a better understanding of which DNA regions contribute to the heritable variation, the scientists investigated the whole genome of 1,600 chickens. Lead researcher Tom Berghof said: “We used genetic difference in the whole genome to identify DNA regions that occur more often in chickens with high Nab levels or in chickens with low NAb levels.”

One region had a very large effect on NAb level, which explained more than 60% of the genetic variation observed. Within this region, one candidate gene could eventually be identified.

Toll-like receptors

“The region contained a few genes. It is very difficult to identify the difference at DNA level that explains the difference in NAb level. Most likely, this difference is due to the Toll-like receptor 1A (TLR1A) gene, which makes this our main candidate.”

TLR1A is a member of the TLR family, an important part of the immune system. This is a group of receptors, a kind of sensor, that recognise common structures on pathogens. “They detect certain parts present on many bacteria or viruses. These sensors therefore have a very broad function. But the association with NAb is new, independent of the specie,” he said.

Applications and future plans

Frans van Sambeek, director of research and development at Hendrix Genetics, said the study offered direct applications for breeders to select layer chickens for increased disease resistance by selecting for this specific DNA region.

“Currently we are investigating how we can apply these research findings into the breeding programmes of pure bred line.

“At the moment, we are running 3 field experiments with layers with high or low NAb levels. These hens will be monitored for livability and production,” he added. In addition, plans are being made to investigate the TLR1A-sensor: “We have good indications that TLR1A is our candidate but this still needs to be proven.” With investigations in this area ongoing, Hendrix Genetics believes that, in the long term, this could result in improved vaccines and health-promoting nutrition. Eventually, this could lead to animals with a higher general disease resistance with lower antibiotic use, lower costs for farmers and higher animal welfare.