Dental problems: Some dental problems, such as tooth pain or a fractured tooth, can make it difficult for a dog to eat. Check your dog's mouth for any obvious signs of dental problems, such as broken teeth, bleeding gums, or excessive drooling.
Esophageal foreign body: Something may be stuck in your dog's esophagus that is preventing food from passing into its stomach. Signs of an esophageal foreign body include regurgitation (bringing up undigested food or water), coughing, gagging, and difficulty swallowing.
Gastric foreign body: Similar to an esophageal foreign body, something may be blocking the outlet of the stomach and stopping food from passing into the small intestine. Signs of a gastric foreign body include vomiting, abdominal pain, and decreased appetite.
Intestinal obstruction: This is a serious condition that occurs when something is blocking the passage of food and fluid through the intestines. The blockage can be caused by a variety of things, such as foreign objects, tumors, or strictures (narrowing of the intestines). Signs of an intestinal obstruction include vomiting, diarrhea, abdominal pain, and a lack of appetite.
Systemic illness: Any systemic illness can cause dogs to stop eating as a result of feeling generally unwell. Common causes include infections, liver disease, kidney disease, and cancer.
It is important to take your dog to the vet if they stop eating to find out the cause of the problem and start appropriate treatment. The vet may recommend diagnostic tests, such as bloodwork, X-rays, or ultrasound, to determine what is wrong.