Animal welfare

How genetic background and early post-mixing social interactions shape dynamic patterns of dyadic aggression in pigs

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Abstract

Pigs are usually remixed into size-uniform social groups when transitioning from nursery to finishing phases, resulting in generalized damaging social interactions such as aggression. Dyadic interactions refer to social interactions between a pair of animals rather than the social behavior of a single individual. Studying the genomic control of dyadic social interactions is gaining traction in animal breeding. The objective of this study is to develop a framework that models the genetic and environmental contributions of individuals participating in dyadic aggression. A linear mixed model was fitted to a pig aggression dataset. The dataset consisted of 10,032 directed dyadic attacks among 797 purebred Yorkshire pigs housed in 59 social groups. The response variable was the total duration of attack in seconds between the initiator (giver) and the recipient (receiver) during a 9-hour post-mixing period as observed from video recordings. Random effects included social group, additive genetic effects, and permanent environmental effects of both the giver and the receiver. Fixed effects included individual and dyad characteristics. A likelihood ratio test indicated that the inclusion of the giver's additive genetic effect significantly improved model fit (P < 0.05). The results showed the giver genetic effect explained a small but heritable proportion of the phenotypic variation (5.6%), while that of the receiver was near zero, indicating that initiating aggression was more heritable. Genetic and permanent environmental components together explained 24% of the total variation in giving aggression, with permanent environmental components accounting for more variance than genetic components. In terms of behavioral interpretations, this suggests that an animal's previous life experiences are more influential in shaping animal-specific aggressive behavior than its genetic makeup. To further disentangle the effects of previous life experiences, we applied a Relational Event Model (REM) to a detailed behavioral dataset with time-stamped serial observations of post-mixing aggression. Our results revealed that pigs that had previously initiated aggression with many other group mates were more likely to initiate future aggression (P < 0.001). For individuals acting as receivers, prior history of reciprocal fights significantly increased the likelihood of future aggression receipt, whereas inverse pressing significantly reduced it, meaning that animals that were involved in inverse parallel pressing earlier post-mixing had a lower risk of receiving aggression later. At the dyadic level, having shared a nursery pen significantly reduced the likelihood of aggression events (P < 0.01). Our findings demonstrate how detailed behavioral phenomics coupled with genomic data can be used to uncover the genetic basis of dyadic aggression in animals. Selection based on estimated breeding values can be applied to reduce aggressive behavior and thereby improve animal welfare. Our event-based analysis also provides insights into how early life experiences influence future aggression behavior.

Keywords: 2026

How to Cite:

Jiang, X., Siegford, J. & Steibel, J., (2026) “How genetic background and early post-mixing social interactions shape dynamic patterns of dyadic aggression in pigs”, World Congress on Genetics Applied to Livestock Production Digital Archive 2026(1): 2284224. doi: https://doi.org/10.31274/wcgalp.23560

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