Traditional methods of selecting poultry lines in individual cages enable to control a key factor in reproduction: the pairing of breeders, and therefore the management of genetic diversity. The end of cage age requires broilers to freely reproduce on the floor where uncontrolled natural selection on reproduction (or sexual seletion) is added to the artificial selection controlled by breeders during artificial selection.

The purpose of this thesis is to understand how the behaviours expressed by males during reproduction on the genetic diversity of breeding lines and, if necessary, to offer solutions against this loss of diversity.  Three strains of broiler chickens with contrasting growth rates will be used as a model to determine wether the results are broad or specific to certain genetics.

For each strain, they will evaluate how the males’free reproduction on the ground impacts (i) their mating with numerous females, (ii) their mating with more fertile females, and (iii) the fertilizaton of a large proportion of the eggs laid by these females, three key steps to maintain genetic diversity of the offspring. Then they will measure how the various stages of uncontrolled selection operate on male sexual traits by estimating selection gradients.

Finally, they will test how to optimize the social composition of groups of breeding males to ensure that paternitty is distributed as evenly possible, and thus maintain the genetic and phenotypic diversity of lines under selection.

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