This paper considers the question whether knowledge on individual coping characteristics of growing pigs may be used to improve welfare and production after mixing. Gilts with either reactive or proactive coping characteristics were identified according to behavioural resistance in a backtest, respectively, being low (LR) and high resistant (HR) in this test. At 7 weeks of age, several pairs of unfamiliar gilts were formed, and pairs and dominance relationships were studied over a 3-week period. The following pairs (combinations) were established: two LR gilts (LR/LR; n=12), two HR gilts (HR/HR; n=12), one LR and one HR gilt (LR gilt dominant: LR(d)/HR; n=11), and one LR and one HR gilt (HR gilt dominant: LR/HR(d); n=12). Results showed that on the day of mixing, aggression subsided less quickly and increases in body temperature were higher in LR/HR(d) and HR/HR pairs. Also, during the first week post-mixing, feed efficiency was lower and skin damage was higher in LR/HR(d) and HR/HR pairs. Mixing of two HR gilts caused highest levels of stress, indicated by greater catecholamine concentrations in urine following the day of mixing, and higher baseline levels of plasma ACTH at 1 week post-mixing. The lower tendency of gilts within HR/HR pairs to contact a novel object may present higher fearfulness. In contrast to those of LR/HR(d) pairs, responses of LR(d)/HR pairs revealed much lower levels of stress, which emphasised the importance of dominance relationships, being independent of coping characteristics of individual gilts. We speculate that in LR/HR pairs, dominant LR gilts were able to suppress aggressiveness of HR subordinates. HR or proactive gilts, however, may become aggressive when being dominant. General effects of social status, independent of combination, were also found. Compared to dominants, subordinates showed higher acute cortisol, body temperature and vocal responses to mixing. In the longer term, they showed a higher vocal and parasympathetic responsitivity towards the novel object, and their body growth was impaired. Measures not influenced by combination and social status included those of leucocyte subsets, prolactin, and average heart rates during novelty tests. To conclude, aggressive conditions in newly formed groups, and consequently welfare and production, may largely depend on coping characteristics of individual pigs, but also on dominance relationships. Accordingly, the practical value of the backtest is being discussed.
Ruis, M. A. W., te Brake, J. H. A., Engel, B., Buist, W. G., Blokhuis, H. J., & Koolhaas, J. M. (2002). Implications of coping characteristics and social status for welfare and production of paired growing gilts. Applied Animal Behaviour Science, 75, 207-231. https://doi.org/10.1016/S0168-1591(01)00191-5