ABGC in collaboration with Hendrix Genetics ISA has developed selection tools for genetic reduction of mortality due to cannibalism in laying hens. A six-generation selection experiment was performed, using a method that takes into account social interactions among group members. Application of this method showed that mortality due to cannibalism can be reduced.
Selection against mortality due to cannibalism
Mortality due to cannibalism is a worldwide problem in the commercial laying hen industry. Cannibalism is the final phase of feather pecking. Currently, beak trimming is used to prevent or diminish the effect of feather pecking. However, beak trimming will or has been banned in some countries of the EU. Therefore, other solutions are needed.
Using a six generation selection experiment, we showed that mortality due to cannibalism in laying hens can be reduced by breeding. This was done by using a selection method that takes social interactions among individuals into account. Thus, selection tools for genetic reduction of mortality due to cannibalism are available. Successful application in a commercial laying hen breeding program still faces a number of challenges, including the large impact of environmental conditions and the limited selection intensity.
Mortality due to cannibalism depends both on the victim that receives the pecking and its group mates that inflict the pecking. Both components , being a victim or actor, can be heritable. Survival of an individual depends on its own genes (direct genetic effect) and the genes of its group members (social genetic effects). Thus both direct and social genetic effects contribute to the heritable variation in survival time in laying hens showing cannibalism. Depending on the breeding line, social genetic effects contribute 33% to 87% of the total heritable variation in survival time. When using a selection method that targets only the direct genetic effect, the survivors are selected. This can result in the selection of individuals that have a good survival, but have negative genetic effects on survival of other individuals. This will result in reduced survival in the next generation. Therefore, a selection method should be used that targets both the direct effect of an individual’s genes on its own survival (victim effect) and the social effect of an individual on the survival of its group mates (actor effect).
Mathematical models show that selection based on relatives kept in family groups, targets both the actor and the victim effects. This method was, therefore, used to select against mortality due to cannibalism in laying hens. Thus individually housed selection candidates were selected based on the survival of their sibs kept in four- or five-bird family groups. In all six generations, selection candidates were selected to breed a high survival line (HIGH). In generations 1, 5 and 6, selection candidates were also selected to breed a low survival line (LOW), and remaining selection candidates were used to breed control (CONT). Offspring had intact beaks. Locations differed over generations.
Response to selection
Realized responses were calculated for generations 1, 5, and 6. Realized responses between HIGH and CONT were 13, -12, and 19 days in generation 1, 5 and 6, respectively. In the three generations, realized responses between HIGH and LOW ranged from 26 through 29 days. A comparison over generations showed that environmental conditions, such as the laying house, had a very large impact on survival time.
Links: 1 minute video made by Quest about this research (in Dutch).