Caused by weaning, an increase of the pH-value in the stomach from under 3.5 to over 4.5 was ascertained; subsequently the values approached 4. In the fore of the jejunum higher pH-values occur, which, after the adaptation to the starter feed, significantly decrease to values around 6. The alimentary coli prophylaxis directed towards the decrease of the stomach-pH is emphasised because different stomach values have their effects in the jejunum as well.