INDIVIDUAL BEHAVIORAL AND PHYSIOLOGICAL STRATEGIES IN PIGS

Previous experiments demonstrated consistent individual behavioral dif ferences in pigs. Some showed a more active behavioral response (so-ca lled A/R pigs), others a more passive behavioral response (so-called N A/NR pigs). In the present study we selected 32 A/R and 32 NA/NR indiv iduals and tested them individually in an open field at 3 (OF1) and 8 weeks of age (OF2). Individual response patterns were remarkably consi stent between OF1 and OF2. While more A/R than NA/NR pigs made escape attempts, the A/R ones vocalized less, and were less inhibited to appr oach novel objects in OF1 and OF2, although they spent less time in ex ploring these objects than NA/NR pigs. Cortisol (CS) level after OF1 i ncreased in A/R pigs but did not change in NA/NR ones, while CS level in OF2 remained constant in A/R pigs but decreased in NA/NR pigs. CS r esponse to ACTH 1-39 was measured at 3 and 8 weeks of age but did not differ between types. Basal CS level was higher in NA/NR than in A/R p igs and accompanied by adrenal hypertrophy. Mean heart rate (HR) was h igher of A/R pigs compared to NA/NR ones in two backtests. HR of A/R p igs substantially increased (23.9 bpm = 15.5%) in reaction to the nove l object in OF2, while HR of NA/NR ones only slightly increased (4.5 b pm = 2.9%), or even decreased (bradycardia). A/R pigs had more often h eart deviations than NA/NR ones. The present study demonstrates that t he two behavioral strategies of pigs are characterized by consistent d ifferences in behavioral, physiological, and endocrine responses to co nflict situations.