The influence of weaning age on post-mixing agonistic interactions in growing pigs

The effects of differences in weaning age on agonistic interactions between pigs after regrouping were investigated, studying 47 piglets from six litters weaned either between 9 and 12 days of age (EW, n = 24) or between 21 and 23 days of age (CW, n = 23). At 9 weeks of age, both EW and CW animals were regrouped into four pens based on their weight (six EW, six CW/pen) and all agonistic interactions within EW pairs and within CW pairs were monitored until 3 days post-mixing. Results indicate that EW animals fought longer than CW pigs on day 1, while no effect of weaning age was found on subsequent days. Furthermore, whereas no significant effects of weaning age were found on the outcome of fights, on day 1, the number of fights not won by the initiator was greater for EW pigs. It is concluded that early weaning of piglets leads to a short-lasting increase in aggression after mixing. Possible mechanisms are discussed. (C) 2004 Elsevier B.V. All rights reserved.