Dogs vomit because stomach contractions cause food to move from their stomach out of their digestive system, according to an article by Norma Bennett Woolf for the Dog Owner's Guide. Although dogs sometimes vomit because they eat grass or too much food, vomiting can also signal that your pet has a more serious disease or illness.

Single-Celled Organisms

Single-celled intestinal parasites, such as coccidia and giardia, often enter a dog's or puppy's body through infected soil, food or water. Infected pets sometimes vomit and/or have diarrhea.

Bacterial and Viral Infections

Bacterial and viral infections, resulting from causal agents such as the salmonella or E. coli bacteria, parvovirus or coronavirus, often cause young dogs or puppies to experience a fever, diarrhea and/or vomiting.

Bloat

Bloat, or torsion, is a life-threatening disease that results from a gas or fluid buildup in the stomach, which blocks off the esophagus, according to Woodhavenlabs.com. This disease causes dogs to develop a distended abdomen, salivation, stomach pain and/or vomiting.

Kidney Disease

Kidney disease in dogs, which results from the inability of the kidneys to filter waste products in blood, can cause pets to experience weight loss, a decreased appetite, dehydration, increased urine output, increased thirst and/or vomiting.

Other Problems

Other problems that can make a dog vomit are pancreatitis, or pancreatic inflammation, diabetes mellitus and gastrointestinal ulcers.

Source:

Dog Owner's Guide: Intestinal Upsets; Normal Bennett Woolf

Woodhavenslabs.com: Gastric Torsion/Bloat in Dogs

Peteducation.com: Pancreatitis

More Information:

Vetinfo: Dog Vomiting

Atlantic Coast Veterinary Conference; The Vomiting Dog-Diagnosis; Todd R. Tams

Petcaretips.net: Frequent Vomiting and Your Dog