Weaning is associated with marked changes in the histology and biochemistry of the gastrointestinal tract (GIT), which decrease digestive and absorptive capacity and contribute to post-weaning diarrhea (Pluske et al., 1997). Increased sus- ceptibility to infections and post-weaning diarrhea are major causes of mortality and morbidity in weaned pigs worldwide and are estimated to account for as much as 50% of the economic losses incurred during production (Cutler et al., 2007). Enterotoxigenic Escherichia coli (ETEC) K88 infection is one of the most important causes of post-weaning diarrhea in pigs (Fairbrother et al., 2005), and oral challenge with ETEC K88 has often been used to evaluate the ability of feed additives to reduce infection or modulate the gastrointestinal microbial response in weaning pigs (