When the esophageal groove forms, liquids bypass the rumen and pass into the omasum and on to the abomasum where most digestion occurs. The formation of the esophageal groove is controlled by neural stimulation from suckling and milk proteins. This means milk, colostrum, and milk replacer bypass the rumen, while water enters it. The esophageal groove forms whether calves drink from a nipple bottle or an open bucket. Feeding milk for an extended time usually results in development of the calf, but limited rumen development because the esophageal groove keeps liquid feeds out of the rumen.