A dog that is vomiting white foam may be suffering from some sort of stomach upset, according to Vetinfo. This commonly occurs if a dog eats something that disagreed with him or takes in water too quickly after exercising, However, if other symptoms are present, it could be a sign of a more serious condition.
If a dog is vomiting white foam, Pet Health & Care recommends keeping the dog off food for 12-16 hours to allow his stomach to settle. If the dog is vomiting the substance in the morning, it's possible he is suffering from bilious vomiting syndrome, or the presence of an excessive amount of bile in the stomach. If this is suspected, the dog should be taken to the vet for a diagnosis.
According to Vetinfo, other possible causes of white foamy vomit include inflammatory bowel disease, bloat or kennel cough. Vomiting due to kennel cough is typically accompanied by a dry cough, runny eyes or nose and lethargy. A dog that vomits white foam could be suffering from parainfluenza or another cold-like illness, with symptoms such as a running nose, fever or sneezing.
If the dog's cough is accompanied by other symptoms, or if it continues regularly, Vetinfo recommends taking the dog to the vet for a full diagnosis.