Relationship between behavioural tests and agonistic interactions at different age levels in pigs

摘要

Fighting among pigs is a normal behavioural pattern to establish a stable rank order. Enhanced aggressive behaviour in pigs in groups lead to increasing stress and injuries especially in mixing situations used as a common procedure in modern pig production systems. In such systems, it is usually not possible to avoid re-housing with unacquainted conspecifics. Hence, due to the lavish analysis of direct or video observations of the agonistic interactions in such mixing situations, there is a necessity to receive easy measurable and practical indicators for predicting individual agonistic behaviour. Possible indicators are standardised behavioural tests such as the backtest and the human approach test. The backtest was performed twice. In each test, the pigs were laid on their backs and held loosely for one minute (n = 1382). The number of escape attempts (NEA) was recorded. In addition to this test, a human approach test was performed four times with weaned pigs (n = 1318) and once with gilts (n = 272). Here, the stockperson recorded the latency of the pigs to approach and touch the person, i.e. the latency count (LC). The agonistic interactions were recorded in a video observation period of 17 h while the traits number of fights (NF) and number of initiated fights (IF) were recorded in mixtures of weaned pigs (n = 1111), growing pigs (n = 446) and gilts (n = 279). The estimations of phenotypic and genetic correlations between these different traits were carried out with animal models in bivariate analyses. The IF trait of weaned pigs and NEA were slightly positively correlated (r(g) = 0.18). Pigs which initiated more fights after weaning had more escape attempts in the backtests. However, there were negative genetic correlations between the agonistic interactions traits NF and IF traits and the NEA backtest trait of growing pigs (r(g) = -0.14 and r(g) = -0.28). The genetic relation between the agonistic NF and IF traits of weaned pigs and the human approach test LC trait of weaned pigs were on a medium level (r(g) = -0.50 and r(g) = -0.45). The genetic correlations between IF and NF of growing pigs and gilts and the human approach test LC trait in weaned pigs were lower but also negatively correlated. Hence, pigs with more NF and IF in mixing had shorter latencies during the human approach tests. Concluding, the backtest and the human approach test might be able to predict the agonistic behaviour of pigs in mixing situations. Nevertheless, the reliability of the predictions of the behavioural tests depends on the age of the pigs at mixing and the previous experiences of these animals. (C) 2016 Published by Elsevier B.V.