Experimental study design.

<p>Two independent experiments with pigs belonging to two different lines (LRFI and HRFI) were performed. The age of pigs at the time of sampling in weeks is indicated. In the experiment with growing pigs aged 12 to 25 weeks, half of the pigs were subjected to sanitary stress from week 12 to 18. Sampling on week 12 was performed just before the start of sanitary stress. Fecal material was collected from pigs from week 4 until week 23 while cecal contents were analyzed from pigs at week 25.