In-feed antimicrobial growth promoters (AGPs) have long been used as means of protection against enteric disorders such as post-weaning colibacillosis (PWC), a diarrhoeal disease of newly weaned pigs resulting from the colonisation and proliferation of enterotoxigenic E. coli (ETEC) in the small intestine. One of the strategies to enable the British pig industry to remain competitive in the global market whilst complying with the imminent removal of AGPs may be to increase weaning age and change the level of crude protein in the diet. If weaning age is increased, sensitivity to PWC may be reduced and pigs be better able to cope with higher levels of protein in the diet, which have been associated with an increased risk of PWC (Prohászka and Baron, 1980). The objective of the current experiment was to investigate the effects of experimental challenge, weaning age and dietary protein supply post-weaning on the health and performance of pigs in the absence of AGPs.