Stress responses in pigs postweaning: Effect of heavier hybrid and weaning intact litters

Early and abrupt weaning of pigs is a stressful event. In addition, the use of hyperprolific sows with increasing numbers of live born piglets has decreased the average pig's birth weight, colostrum intake and weaning weight. The aim of this study was to investigate whether behavioural (tail posture, agonistic and abnormal behaviour), clinical (ear and tail lesions) and physiological (saliva cortisol) indicators of stress postweaning can be minimised by 1) using a pig hybrid that is heavier at birth and weaning, and 2) trough specific-stress-free housing where intact litters of pigs stay in the pen of birth after removing the sow at weaning. The study was a 2 x 2 factorial design, with pigs from Topigs Norsvin TN70 (TN) sows as a heavier alternative to the lighter pigs from DanBred LY sows (DB), and the specific-stress-free (SSF) weaning strategy as an alternative to the conventional weaning strategy (CON) where pigs are regrouped and moved to weaner pens. Fiftyseven litters, on average 26 days of age, were included. Behaviour recordings on the day (d) of weaning (d0), showed that the rate of fights and attacks were 23 and 42 times higher in CON compared to SSF, respectively. Furthermore, on d+1 pig in CON had a 9 (in DB) to 13 (in TN) times higher odds of having clinical ear lesions compared to SSF. Only on d+2, saliva cortisol was lower in TN-SSF than TN-CON, but not lower that DB-SSF. A higher rate of high tail posture was seen in CON d+1, which may reflect higher arousal due to mixing and moving. The rate of belly nosing was 5 times higher in the lighter hybrid (DB compared to TN), but increased from d+7 to d+14 in both hybrids. On d+7 the rate of ear directed behaviour tended to be higher in DB than TN, but the rate increased from d+7 to d+14 in TN to a similar rate as in DB. The rate of tail directed behaviour increased from d+7 to d+14 and tended to be higher in CON than SSF. In conclusion, specific-stress-free weaning reduced agonistic behaviour and ear lesions and tended to reduce tail directed behaviour postweaning. Using the heaver hybrid TN reduced belly nosing postweaning. However, since belly nosing and tail directed behaviour increased over time for both hybrids and weaning strategies additional measures are needed to reduce stress associated with early and abrupt weaning.