Artificial rearing affects the emotional state and reactivity of pigs post-weaning

Artificial rearing involves removing piglets from their mother at 7 days of age and feeding them milk replacer until weaning. Early-life rearing conditions can influence piglets’ mental development, as reflected by their emotional state and reactivity. This study compared the post-weaning emotional state and reactivity of pigs which were either sow-reared (SOW) or artificially-reared (ARTIFICIAL) pre-weaning. Behavioural tests (startle test, novel object test, human-animal relationship test and open door test) were conducted one week post-weaning (weaner 1, 34±0.6 day-old), one week after movement to weaner 2 (69±1.2 day-old) and to finisher (100±1.3 day-old) stages. Qualitative Behavioural Assessments (QBA) were conducted on the same days in weaner 2 and finisher stages. QBA descriptors were computed by PCA and all other data were analysed using linear models. ARTIFICIAL pigs were less fearful of human contact in weaner 1 (45.1 ± 8.43 % vs. 81.3 ± 7.89 %) and finisher (25.8 ± 5.19 % vs. 45.7 ± 6.00 %)stages; but there was no difference in the other tests. ARTIFICIAL pigs had a higher QBA score (more positive) than SOW pigs in weaner 2 (54.49 ± 10.102 vs. 17.88 ± 9.94) but not in finisher (70.71 ± 8.860 vs. 52.76 ± 9.735) stage. In conclusion, ARTIFICIAL pigs appeared to have a more positive emotional state transiently post-weaning and a lower fearfulness towards humans, which are likely mediated by their pre-weaning conditions. These data emphasize the need to consider the entire life of the animals to fully evaluate the long-term impacts of a rearing system.