Megaesophagus occurs when the esophagus muscles do not work, and food and water cannot be moved into the stomach. The food and water trapped in the esophagus will at some point cause your dog to aspirate the contents, which results in aspiration into the lungs and pneumonia.
There are certain breeds in which it is common to have obtained this affliction. These include the wire-haired terrier, miniature schnauzer, Great Dane, German Shepherd, Labrador retriever, Newfoundland, Chines Shar-Pei, Irish setter a greyhound.
Some of the megaesophagus symptoms include regurgitation, refusing to eat, sudden weight loss, exaggerated or frequent swallowing, coughing, sour breath, nasal discharge, low growth, increases respiratory noises, aspiration pneumonia, and excessive drooling.