As in humans, the liver is the largest gland in a dog's body. Its various functions, which include producing bile to digest fats and removing toxins from the bloodstream, are critical to the entire organism. Liver disease is therefore a serious condition that requires immediate veterinary attention. Treatment will depend on the cause and extent of the liver damage, which could be due to a disease, ingestion of a toxic substance or a birth defect.
Poisons and Medications
A number of substances are considered hepatotoxic to canines, which means they are known to cause liver damage in dogs. Some insecticides and rat poisons fall into this category. Xylitol, a sweetener found in some kinds of sugar-free candy and gum, can cause liver damage in dogs if ingested in large amounts. A dog can die from eating mushrooms of the genus amanita or the leaves of the sago palm, which contain compounds -- amatoxins and cycasin, respectively -- that cause severe liver damage. Moreover, dogs can develop liver disease in what is known as an "idiosyncratic reaction" to medications not generally considered hepatotoxic.
Infections and Diseases
Some infections that affect dogs can result in liver disease, including leptospirosis, which is caused by spiral-shaped, waterborne bacteria that penetrate the skin and spread throughout the body; and infectious canine hepatitis, which is caused by a virus. A vaccine can protect your dog against the latter. Young dogs may suffer liver damage as a result of toxoplasmosis, a parasitic infection. The fungal infections coccidioidomycosis and histoplasmosis have been associated liver damage in canines as well. A number of conditions also can result in injury to the liver, including prolonged inflammation of the organ, known as chronic hepatitis; overproduction of the hormone cortisol by the adrenal glands, called Cushing's disease; and diabetes, which can lead to excessive accumulation of fat in the liver.
In normal dogs, blood from the intestines travels through a portal vein to the liver, where it is purged of toxins before reaching other organs. Some dogs, however, are born with a blood vessel that connects the intestines directly to the main bloodstream. This abnormality, known as a portosystemic shunt, can cause toxins to accumulate in the body and interfere with the liver's ability to synthesize proteins, thus hindering the dog's development. Some dog breeds are more prone to congenital portosystemic shunts, including Yorkshire terriers, poodles, pugs, golden retrievers, Labrador retrievers and Irish wolfhounds, among others. Portosystemic shunts also can develop as result of diseases that cause hypertension -- high blood pressure -- in the portal vein that connects the intestines and the liver.
While benign liver tumors rarely cause damage to a dog's liver, the opposite is true of malignant cancers. Primary hepatic cancers -- those that originate in the liver -- are rare in dogs. Dogs who do suffer from such cancers tend to be at least 10 years old. Canine liver cancer is more commonly metastatic, meaning that it has spread to the liver from elsewhere in the body, such as the pancreas.