Newly weaned pigs are at least partially protected against sub-clinical gastrointestinal disorders through the provision of in-feed antimicrobials. Possible associations with antibiotic resistance to life threatening bacterial infections in humans and environmental pollution will result in their ban. As a consequence, gut health and pig performance will be compromised. Current research is aimed at reducing, and eventually overcoming, such consequences through novel nutritional strategies. Effects of the latter on the consequences of sub-clinical infection may be assessed in an infection model, since the absence of in-feed antimicrobials does not always lead to gastrointestinal disorders, due to e.g. variation in infectious environmental conditions. A common gastrointestinal disorder is post-weaning colibacillosis (PWC), which is caused by enterotoxigenic E. coli (ETEC), and is associated with diarrhoea and reduced food intake, and hence reduced performance. Existing ETEC infection models, which have yielded variable results and employed relatively large infective doses of ETEC, have focused on clinical PWC (Madec et al., 2000). The objective of our experiment was to assess whether sub-clinical PWC can be induced through experimental infection with ETEC, and whether such sub-clinical PWC is sensitive to the level of infection used.