Breeding against harmful social behaviours in pigs and chickens: State of the art and the way forward

Harmful social behaviours are prevalent in commercial farming environments and their reduction through economically feasible husbandry changes is challenging. Selective breeding may offer a complementary approach to reduce the expression of these traits. This article explores the progress made in estimating the genetic contribution to harmful social behaviours, the likely consequences of selection on these for production or welfare relevant traits, and the barriers that constrain uptake of selection and how these may be overcome. Significant but often low heritabilities have been reported for all of the major harmful social behavioural traits which may reflect the difficulty of their measurement (pig aggression 0.04–0.43, tail biting 0.05–0.27 and savaging of piglets 0.02–0.9; feather pecking in layers 0.11–0.20). The need for sensitive, easily measured indicators of the likelihood of showing harmful behaviour and estimation of the economic and non-economic benefits of reducing the expression of these traits remain significant constraints to their selection. Routine genotyping and the use of this information for genome-wide selection is advancing rapidly for some species. This methodology is particularly attractive for traits that are difficult or costly to measure and may provide a way of selecting against harmful social behaviours. However, past selection on economic traits may have contributed to the expression of harmful behaviours which could be accelerated by the use of genomic information to more rapidly improve economic traits. Genome-wide selection therefore poses both a threat to welfare and significant possibilities to improve welfare depending on how it is used. Alternatively, selection on associative effects could allow the development of animals that coexist without depressing the growth performance of group members. As effects on group member growth probably operate through social interactions, this may offer an alternative route through which social behaviour can be improved without the need for behavioural phenotyping. Understanding precisely how behaviour will be affected by this approach is crucial and now beginning. Harmful social behaviours ought to respond to selection, albeit slowly, and are the kind of trait likely to benefit most from the carefully managed use of emerging breeding methods, with potential benefits for welfare.