Canker Sore Overview. Canker sores, also known as aphthous ulcers, are among the most common causes of painful sores in the mouth. 1  The classic lesion is a small (less than 1 centimeter) oval to round ulcer with a erythematous (red) border.2  They occur on the mucous membranes inside the mouth.anker Sore Overview. Canker sores, also known as aphthous ulcers, are among the most common causes of painful sores in the mouth. 1  The classic lesion is a small (less than 1 centimeter) oval to round ulcer with a erythematous (red) border.
Other Causes of Heavy Panting in Dogs. Heavy breathing or deep, intense panting can also be a symptom of eclampsia, also called milk fever. Eclampsia is a dangerous condition that affects nursing mothers; low blood calcium levels lead to an inability to stand or walk and tremors.
Telltale signs include dry, hard stools and straining when trying to defecate. Some dogs may also pass mucus when attempting to defecate. What Causes Constipation? There are various reasons why a dog may be constipated: Too much or too little fiber in his diet; Lack of exercise; Blocked or abscessed anal sacs; Enlarged prostate gland