Lesions symptomatic of aggression in pigs

Counting lesions on specific parts of the pig could provide a rapid and genetically validated approach to selecting against aggression, according to SAC’s Simon Turner.

“There has always been anecdotal evidence that breeds do differ in aggression, but even when you look within breeds there is also variability and it is thought that this has a high heritability, with 43% of variation in aggression as a result of the genes they are carrying,” he said.

And minimising aggression is vital from both a welfare and economic point of view, highlighted Dr Turner. “Aggression ultimately causes stress which is a physiological attempt of the body to cope. The stress hormones released are catabolic and burn up tissue and as a result down regulate the immune system. Stress also reduces growth rates, lowers feed efficiency, compromises meat eating quality and hinders conception rates, which is why there are major costs associated with it.”

And while there are techniques that can be adopted to try and reduce aggression such as avoiding mixing or increasing pen complexity by providing barriers for pigs to hide, ultimately this isn’t always possible, which is why breeding against aggression is a better option, according to Dr Turner.

He has found skin lesions are genetically correlated with involvement in aggressive behaviour. “Those pigs with more lesions at the front of their body are predisposed to getting involved in all sorts of aggressive behaviour. Whereas those pigs with more lesions in the middle and rear are more genetically pre-disposed to being bullied,” he explained.

“So selecting pigs by counting the number of lesions and their location will give a good indication of their aggressiveness, which is important when selecting replacements,” Dr Turner added.

However, some people may be nervous about the impacts selecting for reduced aggression could have. “There are long-term benefits to be had and while a slow rate of change in handling ease should be expected, selection will not make pigs lethargic and it will not be selecting against the best growing animals. It will also mean less lesions and more stable social groups and meat quality may also improve as animals will be less stressed.”