Outdoor piglets are reported to eat more readily post-weaning than indoor pigs and show improved post weaning performance (Cox and Cooper, 2001). They are therefore likely to be less reliant on the inclusion of antimicrobial agents in the diet post weaning to enhance performance. Similarly piglets which are older at weaning should also be more resilient and less likely to benefit from antimicrobial agents in the feed. In this experiment we compared piglets reared indoors with those reared outdoors at two different weaning ages to determine whether performance was less dependent on dietary antimicrobial additives in the outdoor-reared older pig.