The Diagnostic Role of Chicken Liver Lesions in Poultry Disease Diagnosis

The liver is soft and brittle in texture, and because it has a rich blood supply, it appears brownish-red. It is the largest gland in the chicken's body and also the largest detoxification organ. It plays a very important role in bile production, blood coagulation, immunity, heat production, and the regulation of water and electrolytes in the body. At the same time, the liver is also a very important barrier structure, so it is susceptible to damage from various pathogenic factors. Different pathogenic factors cause different liver lesions, and therefore different liver lesions have specific diagnostic significance. The types of liver lesions and their diagnostic value in specific diseases are summarized below.

Localized necrotic foci on the liver surface

Focal necrosis of liver cells, focal infiltration of tumor cells, or deposition of foreign material causes yellow-white or gray-white necrotic foci on the liver surface.

In fowl cholera, the liver is brittle and easily broken, with many gray-white necrotic foci ranging from needle-tip to millet size under the capsule and on the cut surface. Microscopic examination: multiple small necrotic foci can be seen in the liver, and characteristic cholera bacteria can be seen within the foci.

In pullorum disease of chicks, the liver parenchyma is covered with white or gray-white nodules the size of needle tips. In addition, the liver may be seen to be enlarged, brick-red in color, with hemorrhagic spots.

In blackhead disease of chickens, the liver surface has chrysanthemum-shaped and reticular necrotic foci, and the center of the ulcerative foci is yellow or gray-green. Microscopic examination reveals red round worm bodies.

In avian tuberculosis, the liver is brittle, often brownish-red, and the liver parenchyma contains gray-white or yellow-white nodules of varying sizes. When multiple lesions fuse, they form cauliflower-like hard nodules. Microscopic examination: this disease is characterized by tuberculous nodules, with caseous necrosis in the center of the tuberculous nodules, which generally do not calcify.

In Marek's disease and lymphoid leukosis, the liver surface has gray-white tumor nodules of varying sizes. The gross appearance of the liver in both diseases is very similar, and differential diagnosis requires comprehensive diagnostic methods.

In aflatoxicosis of chickens, the liver is pale and faded in color, with yellow nodules the size of rice grains on the surface.

Urate deposition syndrome is caused by renal dysfunction due to various reasons, resulting in a large amount of urate deposition in the body. The liver surface of affected chickens has lime-like urate deposits, and urate deposition lesions can also be seen in other organs and tissues. Microscopic examination reveals needle-tip-like urate crystals.

Thickening of the liver capsule with exudate attached to the capsule

This phenomenon is caused by perihepatitis and fibrinous exudation on the liver surface. It is mostly seen in colibacillosis, blackhead disease, and ascites disease.

The main lesions of colibacillosis are thickening of the liver capsule and necrotic foci in the liver, accompanied by pericarditis and peritonitis.

In the early stage of blackhead disease, fibrinous exudation can be seen on the liver surface, and in the later stage, characteristic liver necrotic foci and cecal lesions appear.

In ascites disease, the exuded ascitic fluid contains a large amount of fibrin, which deposits on the liver.

Enlargement of the liver

Many diseases are accompanied by varying degrees of liver enlargement. The following are briefly described:

Fatty liver syndrome: this disease occurs mostly in flocks during the peak laying period or in high-yielding flocks. High-energy diets and insufficient exercise are the main predisposing factors. On necropsy, the liver is enlarged, fragile in texture, and easily broken; the liver shows fatty degeneration, with a faded, earthy-yellow color, and is easily ruptured. Occasionally, small hemorrhagic spots and white necrotic foci can be seen.

Inclusion body hepatitis: this disease is caused by adenovirus and can cause liver enlargement and fading, brittleness, and very distinct hemorrhagic spots on the surface, which can also be seen on the cut surface. Microscopic examination reveals inclusion bodies in the nuclei of liver cells, severe degeneration and vacuolation of liver cells, and hemorrhagic foci formed by the aggregation of red blood cells within the liver parenchyma.

Other causes: many other pathogenic factors can also cause certain damage to the liver, causing metabolic disorders of liver cells and leading to a series of pathological changes such as liver enlargement, degeneration, and necrosis. Examples include pullorum disease, Marek's disease, and blackhead disease of chickens, which will not be described one by one here.

Summary

The characteristic gross (or microscopic) lesions of the liver can only serve as a reference in the diagnostic process. A diagnosis must also be made in combination with the pathological changes of other organs and the feeding and management conditions, and when necessary, serological and other methods should be used for confirmation. Furthermore, modern aquaculture keeps pathogenic bacteria under long-term immune and drug pressure, pathogens continue to mutate, and livestock and poultry diseases are becoming increasingly complex, with characteristic lesions not being obvious. Therefore, it is even more necessary to analyze various factors in the feeding process to make a comprehensive diagnosis.