It does not matter which side of the mouth you insert an esophageal feeder tube. Extend head upward and apply pressure to the corner of the mouth to open. Slowly insert the tube alongside the tongue to the back of the tongue. The calf will start chewing/swallowing, so use this to help get the tube down the esophagus. If the tube is passed correctly, you should be able to feel the ball end of the tube in the esophagus by rubbing your hand on the calf’s skin below the neck. In young calves, it is advisable to pass only about 20 inches of the tube into the mouth and down the esophagus.
Dave Fischer, Extension Dairy Educator, University of Illinois – Illini DairyNET