Stable Pecking Order Can Decrease Aggression in Broiler Breeders

A recent study at the University of Alberta was designed to help understand what factors contribute to the ‘romantic’ and not just aggressive aspects of procreation in male broiler breeder chickens. The study to determine whether or not roosters were aggressive with females and other males in smaller group settings was undertaken by U of A’s researcher Frank Robinson along with Master of Science student Adrienne Herron, livestock welfare technology transfer specialist with Alberta Agriculture and Rural Development., Red Deer.

“The research idea was ‘hatched’ from other university reports of male broiler breeders being very aggressive towards other birds and even attacking people,” says Herron. “We wanted to see if these reports were related to the birds themselves or the environment they are placed in.”

Males were placed into small groups of 30 hens and three roosters. This is a normal commercial stocking density (1-to-10 male-to-female ratio) but at a much smaller scale. The typical barn of broiler breeders is 5,000 birds.

The roosters were rotated out of the pens and new roosters added at four week intervals. The addition of new young roosters to an older flock is called spiking. The rotation of roosters in this study was used to simulate this industry process. Spiking a flock is conducted to increase flock fertility as the presence of younger roosters stimulates the mating behaviours in older roosters. However, the presence of the smaller younger roosters may not only stimulate mating behaviour, but may increase the levels of aggression seen in the overall flock.

“We found that in small groups, male broiler breeders were capable of forming and maintaining a stable social pecking order,” says Herron. “Males were significantly more aggressive for the first day or so after the group was established, but they subsequently settled into a stable pecking order. Each time a new group of males was introduced the aggression started all over again. This research showed that the practice of industry ‘spiking’ likely creates unrest in the social pecking order of the flock and may pose a welfare concern for the smaller younger males.”

A secondary factor was also tested during this research project, that being whether physical size makes a difference. Half of the test rooms were stocked with roosters of the same size while half the rooms had a small, medium and large rooster. The study found that larger roosters were significantly more aggressive than the other two weight groups. Further research conducted by undergraduate student Erica Holm suggested that the presence of one very large dominant male (rather than two of equal size) reduced the amount of time roosters spent fighting.

The difficulty lies in predicting which chicks at hatch are going to become the larger roosters in adulthood. Unfortunately, there doesn’t seem to be a reliable indicator at hatch for which roosters are going to be aggressive towards their flock mates. Further research with a larger numbers of roosters may help to determine early physical indicators of aggression.

This research was jointly funded by University of Alberta, Alberta Livestock Industry Development Fund, Aviagen North America Inc., Poultry Industry Council, and received in-kind equipment support from Alberta Agriculture and Rural Development.

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Stable Pecking Order Can Decrease Aggression in Broiler Breeders