An invasive intestinal disease found in both dogs and cats that results in loosing a significant amount of protein is an inflammatory bowel disease called lymphocytic -
plasmacytic gastroenteritis.
Canine Lymphocytic -
Plasmacytic Gastroenteritis by Scott Trapp, Animal Disease Diagnostic Laboratory Purdue.
This is because another chronic problem, lymphocytic -
plasmacytic gastroenteritis (LPG), can cause the same symptoms.