Case report: hepatic steatosis (fatty liver) in a rabbit
Esther van Praag, Ph.D.
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The liver is one of the biggest organs in the rabbits. It plays an important role in the metabolism of energy by processing nutrients, burning fats, in filtering blood from the digestive system, and in the detoxification of molecules that may damage the body tissues.
Hepatic steatosis, or fatty liver disease, is the abnormal accumulation of fats within liver cells. While the name of the disease hints to fats, it is mainly caused by a diet too rich in carbohydrates, - not fats, which leads to an excessive accumulation of fat in the liver cells that replaces healthy tissue. Instead of metabolizing fats and eliminating the excess, the fatty liver will start to store fat in its tissues. The accumulation of fat in liver cells will interfere with liver functions and metabolism. Impaired functioning of the liver may lead to an accumulation of cellular waste products and toxins in the blood.
Fatty liver disease has been observed in obese rabbits. Causes for this disease are not well understood. Obesity, a diet too rich in fructose (a sugar found mainly in fruit) and carbohydrates (oat), an underactive thyroid gland (hypothyroidism), and lack of exercise are commonly observed. Further causes for fatty liver in rabbits include:
· Anorexia, refusal to take in food caused by dental disease or digestive disorders;
· Lack of fiber in the diet;
· Sickness in obese rabbits;
· Toxins released by certain bacteria, e.g., Escherichia coli. Its toxins can lead to a transient increase of free fatty acids in the blood.
There are no clinical signs associated to hepatic steatosis in rabbits. Tiredness, discomfort, anorexia, depression and/or jaundice may appear when fat accounts for about 10% of the liver weight.
Waste of muscle tissue is observed and can lead to reluctance to move and exercise.
Diagnosis of hepatic steatosis is based on visual examination and a complete blood test. Radiography and ultrasound of the chest and abdomen can help determine the shape and enlargement of the liver as well as the extent of fat excess in the liver.
The presence of gallstones composed of excess cholesterol may be detected.
A blood panel will usually show elevated liver enzymes, indicating inflammation of the liver tissue. Fat oxidation will lead to damage of liver cells, rupture of their membrane and leakage of liver enzymes into the bloodstream. Typically:
· Alkaline phosphatase (Alk phosphatase) is elevated.
· Alanine transaminase (ALT) is elevated.
· Aspartate transaminase (AST) is in the so-called "grey zone", just above the reference range.
The AST/ALT ratio is lower than zero (in this case: 103/141 = 0.73). This is indicative of viral liver disease or steatosis/fatty liver disease linked to obesity.
In this case, there is no liver failure yet. Indeed, gamma glutamyl transpeptidase (GGT) is decreased and below average. This marker is more sensitive than ALT and AST to liver damage, but less specific. In case of damage GGT increases rapidly.
Hyperlipidemia and elevated triglycerides can accompany fatty liver disease. The abnormally high level of cholesterol, indicating cholesteremia, remains unexplained. In rabbits it is usually associated with liver failure, obesity, and, rare in pet rabbits, a diet rich in fats.
Glucose is high, but within range, ruling out insulin resistance and obesity-related diabetes.
An elevated blood level of monocytes is nowadays believed to be a marker for fatty liver disease (e.g. obesity).
Measures must be taken without delay to reverse the liver damage and to eliminate the excess of fat in that organ. The treatment of fatty liver disease is slow and long. It aims at reversing the fat metabolism in the liver and duration depends on the extent of fat accumulation (in rats fed a diet high in carbohydrates, it has been shown that they developed a fatty liver in proportion of the amount of sugar fed. This can, furthermore, be accompanied by insulin resistance.).
The rabbit should not receive any further carbohydrate rich food and treats. Instead, it should receive a healthy fiber-rich diet, rich in hay (see: Rabbit feeding for suggestions).
Obese rabbits must lose weight. This process is gradual process – a 5 to 10% loss of initial body weight over the next 6 months.
The administration of milk thistle (Sylibum marianum) extracts may help in the healing and recovery of the liver cells.
Without correction of the diet, the liver tissue will be progressively replaced by scar tissue, which prevent the normal circulation of blood within this organ. Fibrosis and regenerative nodules (lumps that occur as a result of a process in which damaged tissue is regenerated) will develop and replace the healthy liver tissue, leading to loss of liver function (cirrhosis) and liver failure complications.
During the recovery process, the loss of weight may not be linear and gradual. It may stop during a few weeks, than decrease more. This is normal and does not mean that recovery has stopped. The level of liver enzymes in the blood may, furthermore, fluctuate, before decreasing to normal.
Prognosis for hepatic steatosis is guarded, especially in older rabbits.