The backtest as a possible tool to improve welfare of pigs after mixing

摘要

In domesticated pigs, representatives of proactive and reactive coping styles are found. Proactive animals are more aggressive than reactive animals, and this aggression may be predicted from behavioural resistance in a backtest. High resistant (HR)and low resistant (LR) gilts, respectively representing the aggressive and the low-aggressive animals, were selected at 3 days of age. At 7 weeks of age, pairs of unfamiliar gilts were formed and studied during three weeks. The following combinations were distinguished: HR/HR (n=12), LR(d)/HR (LR gilt dominant; n=11), LR/HR(d) (HR gilt dominant; n=12) and LR/LR (n=12). In the first week after mixing, welfare was most impaired in HR/HR and LR/HR(d) pairs. Relatively high levels of aggression (at day 1)and scores of fresh skin lesions (at days 2 and 7), indicating the least stable social structures demonstrated this. Moreover, the feed/gain ratio was higher in these pairs. At 1 week after mixing, baseline HPA-activity and responses to a novel object suggested highest levels of stress and fear in gilts of the HR/HR pairs. Whereas characteristics and responses of LR/LR pairs were 'intermediate', social stability seemed to be most prominent in LR(d)/HR pairs. Though dominance-submissive relationships inLR/HR pairs prominently affected welfare, it could not be predicted which animal became highest in rank. For practical implications and from a welfare point of view, it is therefore concluded that it should be avoided to mix pigs into pairs of HR animalsonly. This may also apply for larger groups consisting of many HR animals.