Commercial production environments can exacerbate fighting between pigs by mixing unfamiliar animals together and restricting opportunities for escape from aggression. Fighting has welfare and economic costs but is not easily improved by economically feasible changes to the environments in which pigs are kept. Pigs vary in aggressiveness and this SRUC-led research has shown that this is heritable across generations. The project, partners in which as based in the UK, Sweden, Germany and France has developed a way of breeding against aggressiveness and has assessed the welfare consequences of doing so.
Our work has sought to understand the genetic basis to aggressiveness to complement continued efforts to find a way of improving the environment to minimise fighting. Aggressiveness is a complex trait and assessing it on a large number of animals very rapidly, as would be required for commercial breeding, is difficult. Furthermore, it is critical to understand the wider consequences of breeding for less aggressive animals, both for animal welfare and farm productivity.
In 2009 the EU slaughtered 244 million pigs, most of which would have been mixed into new social groups and experienced the costs of fighting during their life. Pigs in many other non-EU countries also experience fighting.
Fighting results in skin lesions which are likely to compromise welfare and increase the risk of infection. It also results in reduced feed intake, poorer growth, poorer efficiency of feed use and greater risk of lameness. Although it is difficult to quantify the full economic costs of fighting, they are likely to significantly depress economic efficiency in a sector with small profit margins.
Our work has shown that approximately 30% of the variation in aggressiveness between pigs results from the genes that they carry. This is comparable to traits such as growth rate which have been improved dramatically in recent decades through selective breeding. Aggressive behaviour should therefore respond to breeding at a comparable rate.
“SRUC research is helping to reduce aggression which, globally, is one of the most significant welfare challenges facing commercially produced pigs.”
Achieving this is dependent upon an ability to measure individual aggressive tendency very quickly and accurately on large numbers of animals on commercial farms. We have validated that the number and location of skin lesions, when taken together, provide a robust estimate of the genetic tendency of a pig to become involved in reciprocated fighting and one-sided bullying of others. The tendency of individual pigs to accumulate skin lesions persists over a period of at least 3 months and therefore is a stable characteristic of the animal.
We have worked with major pig breeding organisations to assess the consequences of breeding animals on the basis of their tendency to receive lesions as an indicator of their aggressiveness. Unaggressive pigs are no less active than aggressive pigs but they do respond to handling in a slightly different manner, the implications of which for the animal and handler deserve further investigation. Unaggressive pigs tend to produce meat of superior eating quality but there is evidence in one population that the fastest growing and most feed efficient pigs have a genetic tendency to be the most aggressive.
This last finding suggests that breeding against aggressiveness will require careful targeting to ensure that progress in economically important traits is not compromised. We are now working with commercial breeders to allow the implementation of this knowledge in selection decisions. Whilst breeding may offer a means of reducing aggressiveness to a level more akin to that seen in the wild, it should complement and not replace efforts to find ways of reducing fighting through changes to the housing environment.
This work was funded by the EU under the Framework 6 and SABRE initiatives, BBSRC, Defra Link, the Scottish Government, RSPCA and Scottish SPCA.
University of Uppsala (Sweden), Leibniz Institute (Germany), INRA (France), Genus plc (UK), Quality Genetics (Sweden), JSR Genetics (UK)