Individual differences in responses of piglets to weaning at different ages

Several studies indicate each piglet within a litter is affected differently by weaning and that these individual responses may be altered by the age of the litter at weaning. In the present study, eight litters of individually marked piglets (n = 79) were randomly assigned to be weaned at 21 or 35 days (four litters per treatment), and behavioural and physiological measures were used to elucidate the relationship between age and weaning, and the within-litter variation in short-term. responses to weaning that is thought to occur. Weights, vocalisations, littermate directed behaviours, suckling related parameters and salivary cortisol concentrations were recorded for individual piglets on both treatments from birth to 37 days of age. The time piglets spent at the udder, massaging or suckling, gradually increased over the preweaning period, as did aggression, nosing and chewing of littermates. Higher levels of aggression were found on the day of weaning relative to the 2 days following, whilst vocalisations did not peak until the day after weaning. Salivary cortisol was found to be lower for D35 piglets (day x treatment effect: F-2,F-116(38) = 2.67, P = 0.073) and 'high vocalisations' twice as high on the day after weaning for D21 piglets compared to D35 (day x treatment effect: F-2,F-146(8) = 3.93, P < 0.05). Irrespective of weaning age piglets that suckled anterior teats during lactation were found to be of heaviest relative weight throughout the preweaning and postweaning periods. Weaning caused relatively heavier piglets to 'high vocalise' less, 'low vocalise' more and be more aggressive. Anterior teat suckling piglets were also found to have high salivary cortisol levels postweaning. The results provide evidence that weaning piglets at 21 days is detrimental to piglet welfare. Direct support was also found for piglet teat choice to determine a piglet's response to weaning. The increase in low frequency begging calls by larger piglets along with the increase in high frequency separation calls by smaller piglets postweaning suggests that heavier, anterior teat suckling piglets may experience more nutritional deprivation whilst smaller, posterior teat sucklers may experience more maternal separation stress. Therefore, individual differences in short-term response to weaning exist and are correlated with piglet weight and individual teat choice during lactation. (C) 2002 Elsevier Science B.V. All rights reserved.