Consequences of weaning piglets at 21 and 28 days on growth, behaviour and hormonal responses

A recent European Directive raised the minimum weaning age of piglets to 28 days, although weaning at 21 days is still allowed (but not necessarily practiced) in batch breeding conditions. The aim of the present study was to determine the consequences of weaning at 3 and 4 weeks on animal weight gain, behaviour and stress neuro-endocrine responses, compared to sow-reared piglets. Three groups of Large-White piglets were compared: six litters of seven to eight piglets weaned at 21 days (W21 group), six litters of seven to eight piglets weaned at 28 days (W28 group) and six litters of eight suckling piglets reared by the sow for 40 days (C group). Piglets were regularly weighed from birth to 75 days. Each weaned group was observed for 2 h/day for 7 days (between d - 1 and d + 12 after weaning) at the same time as the control group. The specific behavioural parameters assessed by direct observation were position, activity and social interaction. Urine was collected to measure glucocorticoid (cortisol and cortisone) and catecholamine (adrenaline and noradrenaline) levels. Compared to nursed piglets, weaning at 21 or 28 days induced a reduction in growth rate, as well as behavioural and hormonal changes. Early behavioural changes included an increase of vocalisations and of lying in litter cohesion; later changes included an increase of aggressive and nosing behaviour. Endocrine changes included a reduction in catecholamine (mainly noradrenaline) and cortisone levels in urine. Comparison of W21 and W28 showed that some of these changes were more intense and lasted longer with early weaning. Endocrine changes and certain behaviour (litter cohesion, vocalisations) could be related to food intake deficits, as measured by the greater reduction in growth rate in early-weaned animals. Changes in active behaviour (increase of aggressive and nosing behaviour) appeared earlier after weaning in the youngest animals. This study shows that weaning at 21 days has more negative consequences on growth rate and stress endocrine responses than weaning at 28 days. However, piglets weaned at both 21 and 28 days showed behavioural disturbances, but often with different kinetics. (c) 2005 Elsevier B.V. All rights reserved.