[Influence of weaning method on the behavior and the hypophyseal-adrenal axis activity in the piglet]

The pituitary-adrenal activity and behavioural reactions of 3-week weaned piglets kept in flat-decks were compared with those of 6-week weaned piglets kept in the maternity pen. Early weaning induced a transitory increase of plasma corticosteroid levels, while 6-week weaning did not influence those levels. Lower plasma corticosteroid levels were observed in piglets kept with the sow during post-natal weeks 4 and 5. To assess whether early weaning would affect subsequent reactivity, both groups of piglets were individually submitted to an open-field test, a neophobia test and a continuous avoidance schedule when they were 7-9 weeks old. Early-weaned piglets reacted less to the open field test, but pituitary-adrenal response was the same in both experimental groups. Early-weaned piglets were slower in approaching a new object (a food container) in a familiar environment (neophobia test), suggesting that they were more neophobic than 6-week weaned piglets. Avoidance conditioning performances were different in the two sexes: females had the same score whatever their previous rearing conditions, while 6-week weaned castrated males were relatively deficient in learning the task. Taken as a whole, the behavioural and pituitary-adrenal differences observed in the present study do not indicate that early weaning in flat-deck has long-term detrimental effects on the adaptive abilities of pigs.