Individual differences in aggression and physiology in peri-pubertal breeding gilts

Several recent studies on pigs have demonstrated a relationship between the degree of resistance displayed in a so-called backtest and a variety of behavioural and physiological responses in piglets and young fattening pigs, However, the discussion about the predictive power of the backtest is still going on. This study aimed at investigating the relationship between the backtest response and behaviour and physiology in peri-pubertal, i.e. nulliparous breeding gilts. During the suckling period gilts were subjected to the backtest. Piglets classified as low resisting (LR, n = 36) and high resisting (HR, n = 36) were selected. At 20 weeks of age they were housed in groups of six (three HR, three LR), Between 23 and 29 weeks of age, behaviour and physiology under undisturbed conditions were measured. At 26 weeks of age, LR pigs showed higher baseline salivary cortisol levels during the light period than HR pigs. However, HR and LR gilts did not differ in weight gain, aggression and heart rate response to afternoon feeding. This study indicates that when breeding gilts are kept in groups containing both HR and LR animals, aggression and heart rate reactivity under undisturbed conditions do not relate to the backtest response. (C) 2002 Elsevier Science B.V. All rights reserved.