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×treatment effect: F 2,116(38)=2.67, P=0.073) and ‘high vocalisations’ twice as high on the day after weaning for D21 piglets compared to D35 (day×treatment effect: F 2,146(8)=3.93, P