Disorders of the Liver in Horses

Last Updated on March 29, 2022 by Allison Price

The liver performs many functions. It can also be used to metabolize carbohydrates, proteins and fats. It also helps to eliminate and break down many potentially harmful compounds. The liver is vulnerable to injury and disease because of this. The liver is protected against permanent damage by having a large functional and storage capacity.Liver Functions in Horses

Horses’ Liver Functions

Metabolizes fats and carbohydrates.Metabolize drugs (inactivates them or makes it easier to expel them).Stores, metabolizes and activates vitaminsMinerals, glycogen, triglycerides, and other nutrients are storedProduces proteins necessary for different body functions like blood clotting.Produces the bile acids necessary for digestionDetoxifies any harmful products that have been produced in the body (such ammonia), or are consumed by animals (such poisons).Influences immune responsesExtramedullary hemotopoiesis helps to develop blood cells

Liver cells that have died are destroyed by inflammatory cells. They are replaced with new cells or fibrous tissue. Horses and foals can develop liver disease, but it is not often fatal. If the problem is not severe and new liver cells can be regenerated, horses with liver disease are usually in a bad position. If caught early, liver fibrosis can be reversed. A long-term condition that causes severe damage to the liver and leads to fibrosis, a serious sign. There is little hope for recovery.

Signs of liver insufficiency

The signs of liver disease may not become apparent until the liver becomes nonfunctional, or if there is a disease in another part of the body. It is possible to overlook signs such as depression or decreased appetite in the early stages. Horses with liver disease or liver failure are more likely to experience jaundice (yellowing the skin, gums and whites of their eyes), abnormal behavior (below), and weight loss (). Skin changes due to a reaction to ultraviolet sunlight (photosensitization), fever, or abdominal pain (colic) may occur. There may also be constipation or harsh, high-pitched breathing sounds. Horses with liver dysfunction may experience anemia from parasitic diseases, certain plant poisonings, long-term inflammatory diseases or the destruction of red blood cell. Horses with severe liver disease may experience abnormal bleeding because their liver produces important clotting protein. Long-term liver disease may cause weight loss, which can be the first sign of liver abscess.How does Liver Disease affect the Skin (Light Sensitivity, Photosensitization).

How does Liver Disease affect the Skin (Light Sensitivity, Photosensitization).

The liver’s main function is to remove toxic substances from the body. The bloodstream is flooded with phylloerythrin when the liver becomes diseased. The horse eats chlorophyll, which is a green pigment. Phylloerythrin can be produced from the breakdown of this green pigment. It is also sensitive to light. When phylloerythrin is in contact with the skin, it releases energy that damages the skin. Unpigmented or light-skinned areas absorb the most ultra-violet light, so they are most likely to be affected by light sensitivity (photosensitization).

Hepatic Encephalopathy is a condition that causes neurologic problems due to poor liver function. It can be seen in many liver diseases. The liver removes any poison from the bloodstream. If the liver isn’t working well, poisons can build up and cause nerve damage.

Hepatic Encephalopathy signs may include:

  • Depression
  • Lethargy
  • Head pressing
  • Circulation
  • Walking aimlessly is not a good idea
  • Lack of coordination
  • Trouble swallowing
  • persistent yawning
  • Sleepiness
  • Increased friendliness
  • Eating non-food items (pica).
  • Aggressiveness
  • vicious behavior
  • Stagger
  • seizures
  • coma

Some cases of liver disease, particularly in horses, can cause loud breathing sounds and difficulty breathing. Although these signs are often severe, hepatic-encephalopathy can often reverse itself if the underlying liver disease can be treated. Horses suffering from hepatic-encephalopathy can be aggressive and unpredictable, which can lead to injury to their handlers or horses. Sedation may be required for the animal.

photosensitization is a form of liver disease that can lead to hypersensitivity to UV sunlight. The bloodstream has a higher level of light-reactive chemical called phytoerythrin. Itching, mild to severe skin diseases, reddened skin, fluid accumulation under the skin (edema), skin ulceration, peeling, eye inflammation, tearing, aversion of light and cloudiness of your cornea are all possible signs. Edema and skin inflammation are more common in nonpigmented, light-colored, or hairless parts of the body that are exposed to the sun. The underside of your tongue could be affected, which is not common. Sometimes, blindness, skin abnormalities, loss or death, as well as other health problems, can occur.

Horses with liver disease can experience diarrhea or constipation. Horses and pony with hyperlipemia (high blood fat levels) or liver failure can develop diarrhea, founder (laminitis), fluid accumulation under the skin and edema. Horses with liver disease may experience intermittent diarrhea or constipation. Horses suffering from liver disease and hepatic embolism often experience intestinal impaction or obstruction as a result of decreased water intake.

Your veterinarian will first treat your horse for severe hepatic disease. He will also stabilize it and conduct laboratory tests. Before recommending a long-term treatment plan, or giving you an outlook on the horse’s future, your veterinarian will perform a liver biopsy. This will determine whether there are any tissue changes and if there is liver fibrosis.


Sometimes, laboratory tests can detect liver disease before it becomes serious. Routine biochemical tests, such as blood levels of liver-specific enzymes, can be used to detect liver disease. However they don’t measure liver function. There are additional biochemical tests that can be used to assess liver function. These tests provide the veterinarian with an important tool for diagnosing.

Signs, history, physical examination and blood tests can all be used to determine the extent of liver disease in horses. A liver biopsy is the best way to diagnose. The tissue can be examined to determine the severity and causes of liver disease. Ultrasonography can also be used to assess the size and appearance the liver or the bile duct, gallstones, tumors or other abnormalities. Contrast studies can be used to diagnose foals with secondary liver disease and intestinal obstructions. In some cases, additional specialized tests such as scintigraphy may prove helpful. This is where a radioactive substance injects into the body and its distribution is studied.

Treatment and Management

Horses with liver disease or failure should be treated to prevent injury to themselves and others. Horses with liver disease symptoms may need to be treated immediately. The causes of liver disease, liver function, liver scarring, and bile duct obstruction are all factors that will determine the specific treatment.

The best treatment is when it is done early and liver fibrosis is not severe. Horses suffering from severe fibrosis are less likely to respond because their potential for regeneration of healthy cells in the liver is reduced.

Horses with hepatic-encephalopathy may need to be sedated to avoid injury to them or their handlers. Additional therapies may be required to decrease the absorption or production of ammonia, a byproduct from protein metabolism and which can lead to hepatic-encephalopathy. You can correct conditions like low blood sugar, acid-base, and electrolyte imbalances with intravenous fluids. If the horse is able to swallow normally, it should have adequate fresh water. Broad-spectrum antibiotics can be prescribed for liver infections until the cause of the disease is determined. Low to moderate doses nonsteroidal anti-inflammatory medications may be used to manage pain. Some horses may require vitamin or antioxidant supplements. Horses suffering from liver disease should be kept out of the sun.

Animals with hepatic disease or liver disease need to be managed in their diet. Horses with hepatic encephalopathy or liver disease should be given careful food as they may have difficulty swallowing. Your veterinarian will give you specific instructions on proper feeding. Horses with liver disease need to be fed regularly in small quantities. The recommended diet is rich in easily digestible carbohydrates, adequate protein, and a high level of starch. Horses that refuse to eat will need intravenous fluids or stomach tubes.

Acute Hepatitis (Short-term Liver Inflammation)

Acute liver inflammation is a sudden, temporary inflammation of the liver. It can be caused either by infection, poisoning, or other undetermined causes. Lethargy, jaundice and poor appetite may all appear suddenly. You may also notice sensitivity to light, diarrhea and abnormalities in blood clotting. Horses with severe and sudden liver disease may experience neurologic signs such as low blood sugar or hepatic. There may be signs of a bacterial blood infection. Potassium deficiency can be caused by a loss of appetite.

Idiopathic Acute Liver Disease, (Serum Sickness and Theiler’s Disease).

Acute hepatitis in horses is most commonly caused by idiopathic acute liver diseases. This is a sudden-onset, undiagnosed liver disease. About 20% of horses suffering from this disorder develop liver disease within four to 10 weeks of receiving antitoxin derived from horses. Sometimes, though the horse with the disease may not have received it, they may have come into contact with another horse who did. Horses that have been given equine blood products such as serum or plasma can also get the disease. This condition is often called serum-associated liver disease or serum sickness. Horses can get this disorder even if they have never been exposed to such a product. It is not known what causes the disorder. There are two possible causes: a viral infection and an overreaction of the horse’s immune systems. The chances of a horse getting tetanus antitoxin in foaling are higher for lactating mares.

The signs usually appear suddenly and can progress quickly over a period of 2-7 days. Horses with idiopathic acute liver disease can suddenly die in as many as 50% to 60% of their animals. The overall death rate for affected horses is as high as 88%. Idiopathic acute liver diseases in horses can cause loss of appetite, hepatic and encephalopathy (see below), as well as jaundice. The nervous system signs can range from lethargy and aggression to maniacal behavior, blindness and poor coordination. You may notice light sensitivity, colic and fever. Although most cases involve one horse, there have been reports of outbreaks involving multiple horses. One horse should not be considered sick if there are others in the group. All horses should be tested for liver disease by a veterinarian.

The horse’s history, sudden symptoms, and blood tests are all used to diagnose the problem. Ultrasonography can also be useful. To confirm the diagnosis, a liver biopsy is required.

The disease is not treatable. Treatment for hepatic-encephalopathy can be supported and often is successful. Moving horses or weaning mares’ foals can cause hepatic dysfunction. These situations should be avoided if at all possible. The severity of liver damage will determine the extent of recovery. The likely outcome can be guessed by your veterinarian. Horses that are stable for three to five days and continue to eat frequently often recover. The long-term outlook for affected horses is positive. Some horses may experience continued weight loss or death in the months following the initial signs.

Tyzzer disease

The bacterium Clostridium Piliforme causes Tyzzer disease. Foals between 1 and 6 weeks old can get the infection. It causes liver damage, inflammation, and diarrhea. Although rare, it is often fatal. It can often be fatal to foals that are apparently healthy and fast growing. Foals are more likely to contract the disease if they are young and if nursing mares are allowed to visit farms where the bacterialspores exist. It is less common in older mares’ suckling foals. Although the bacteria can be found in the stomachs of older foals and adults, it is not common in them.

Disorders of the Liver in Horses

Infection signs, such as depression, fever, jaundice and loss of appetite, can quickly develop and last for a few hours to a couple of days. Many foals are found dead or in a coma after an infection. The signs and laboratory results of blood, urine, or tissue tests are used to diagnose the foal. Although there is no cure, supportive care can be offered.

It can be present on farms year after year. Although many foals can be exposed to the disease, only a small number (usually those with a compromised immune system) will develop the fatal form. To minimize the risk of developing disease, a veterinarian will recommend these facilities.


Cholangiohepatitis refers to inflammation of the liver and bile ducts. It can sometimes lead to liver failure in horses. Sometimes, it is associated with small intestinal obstructions, tumors and inflammation, as well as stones in the liver. Cholangiohepatitis can be caused by a variety of factors, such as bacterial infection in bile duct, small intestinal motility problems, parasite migration and decreased intestinal motility.

Cholangiohepatitis can be a long-term, medium- or even permanent disease. The symptoms of cholangiohepatitis include weight loss, colic, low appetite, fever, and colic. Light sensitivity and jaundice may also be signs of hepatic-encephalopathy (see above). Sometimes, severe blood poisoning or death may occur from short-term cholangiohepatitis. A liver biopsy is used to confirm diagnosis. If stones are present, ultrasonography can detect them.

If a test shows a specific type of infection, antibiotics can often be used to treat it. The treatment should continue for at least 4 to 6 weeks. It may be necessary to continue support care such as intravenous fluids and therapy for hepatic-encephalopathy. To determine if the treatment is working, liver enzyme tests and biopsies will need to be performed again. Broad-spectrum antibiotics may be prescribed if test results are not clear or unavailable. If fibrosis (scarring), is not severe, the outlook is positive.

Poisons that Affect the Liver

Hepatotoxins poisons the liver (see below Table: Substances That Can Cause Liver Injury in Horses). If the initial poisoning is severe, liver damage can lead to fatal liver failure. The liver damage caused by toxins is more common if it occurs over a prolonged period. Cirrhosis is a condition where the liver’s functional tissue is replaced with fibrous tissue. Many hepatotoxins, especially in plants, can have toxic effects on multiple organs including the kidneys and lungs.TABLESubstances That Can Cause Liver Injury in Horses

Obtaining a definite diagnosis may be difficult. To determine the toxic agent, it may take careful history, examination of the environment, laboratory testing, and/or liver biopsy. In the stomach contents of some people with short-term toxic plant effects, toxic substances may still be present.

There are not many anti-hepatotoxins. To reduce exposure, it is important to remove horses from the source. It may be necessary to alter the horse’s pasture, hay, or remove any toxic plants from the area. To reduce the amount of toxic substances absorbed, your veterinarian might recommend laxatives such as magnesium sulfate or mineral oil. For long-term toxicities, such as pyrrolizidine toxicity due to plants, these may not be effective. Treatment often involves dietary management and fluid treatment to correct electrolyte (salt), metabolic and blood sugar problems. Hepatic Encephalopathy (see above), must be managed. If light sensitization is present, avoid sunlight. To prevent skin infection, antibiotics may be prescribed. Recovery is uncertain and will depend on the specific toxin.

Gallstones (Biliary calculi, Choleliths).

Horses do not have a gallbladder. However, stones can build up in their bile tubes (biliary stones or calculi). Although these stones can block the bile ducts in horses and cause liver disease (sometimes they don’t cause any symptoms), No matter what breed or sex, gallstones are most common in middle-aged horses (6-15 years old). The bile ducts may contain one or more stones. Gallstone formation in horses is unknown.

Gallstones and bile duct inflammation are common signs in horses. These include weight loss, jaundice, depression, and even fever. Light sensitivity and hepatic dysfunction are less common signs of liver disease. These symptoms can often disappear. Persistent abdominal pain may indicate a complete obstruction of the common gallbladder. Additional evidence of the disease can be found in blood tests. Ultrasonography can reveal liver enlargement and the presence of stones.

Sometimes, bile duct obstruction can be fatal in horses. However, it is possible to crush or remove the stones surgically. If the stones are small, intravenous fluids or medication can be used to dissolve them. To reduce inflammation and pain relief, anti-inflammatory drugs may be used. If an infection is possible, antibiotics may also be prescribed. To manage liver problems, support care is offered.

Chronic active hepatitis

Chronic active liver disease refers to liver inflammation that causes liver disease. Cholangiohepatitis, as mentioned above, can also be part of chronic active liver disease. Although the exact cause of inflammation is unknown, it may be due to infection, the immune systems, or toxins. Acute hepatitis may progress to chronic active liver disease from many causes.

Weight loss, depression, lethargy, and poor appetite are the main symptoms. Sometimes, there may be jaundice, behavior changes, diarrhea and light sensitivity. Fever can be intermittent or persistent. A liver biopsy can be examined microscopically to confirm a diagnosis. To check for bacteria, your veterinarian might order a tissue culture.

Treatment includes fluids that contain potassium chloride, glucose and vitamin supplementation, dietary management (a low protein, high branched chain amino acid diet, high carbohydrate diet), and avoiding sun exposure if possible. Corticosteroids can be used to treat inflammation and fibrosis, as well as broad-spectrum antibiotics for infection. There may be other types of medication that are needed. Horses with less severe tissue abnormalities are likely to have a good outlook, particularly if they respond well to corticosteroids. Horses with liver disease, liver scarring, or loss of normal liver cells are at risk.

Hyperlipemia and Hepatic Lipidosis

Hyperlipemia refers to a condition in which blood fats (triglycerides and lipids) rise. Another aspect of hyperlipemia is fatty changes in the liver (hepatic liposis). Hyperlipemia syndrome may be caused by poor feed quality, decreased feed intake, or stress-related changes in energy (such as pregnancy or illness). The winter and spring are the most common seasons for hyperlipemia.

This disease is caused by the need to obtain energy. It causes excessive movement of fatty acid out of fat tissue. This leads to high blood cholesterol levels and fat accumulation in the liver. Hyperlipemia is most common in miniature horses, ponies, and donkeys. It is less common in adult-sized horses. Hyperlipemia is a condition in which ponies become obese due to recent weight loss, stress, illness, pregnancy, early lactation, or other factors. Hyperlipemia can occur in miniature horses or donkeys with other illnesses.

Hyperlipemia can cause weakness, lethargy and poor appetite. There may be a history of weight loss, severe obesity, or a prolonged loss of appetite. You may experience weight loss, colic and fluid accumulation under your skin. Common signs include impaired liver function, dysfunction of the kidneys, heart, and skeletal muscle functioning. The history, signs and physical examination are often used to diagnose the condition. A diagnosis is confirmed by high blood triglyceride levels. High levels of cholesterol may also indicate the presence of this disease. Additional evidence is provided by laboratory tests that show poor liver function.

The most important factors in treatment are intravenous fluids and nutrition support. If the horse is able to eat enough food, voluntary feeding is preferable. However, tube feeding may be required until adequate feed intake. Intravenous nutrition may also be required for horses who refuse to eat. Injections of insulin and heparin may be required for some horses. It is essential to ensure that miniature horses, donkeys, ponies, horses, and donkeys eat adequate food during stressful times, illness, pregnancy, and other periods.

Hyperlipemia can cause death in small breeds. Most cases of hyperlipemia are preventable if the underlying disease is treated. Ponies and standard-sized horses with hyperlipemia have a poor outlook.

Horse Liver Tumors

Horses are very rare to have tumors that first develop in the liver. Cholangiocarcinoma, which is the most common type, is more common in older horses. Tumors can also develop in the liver from other areas of the body. Lymphosarcoma, the most common form of blood cell cancer in horses is 41%.

The following Signs indicate that tumors originate from the liver:

  • Lethargy
  • weight loss
  • An enlarged stomach
  • jaundice
  • Liver failure

Lymphoma symptoms can include weight loss, lethargy, and decreased appetite. Lymphoma that spreads to the liver can cause severe depression, liver failure, jaundice and liver damage. Although liver tumors can be diagnosed using blood tests and ultrasonography (which are both valid methods of diagnosing them), a biopsy is required to confirm the diagnosis. Your horse’s signs and the type of tumor will be used by your veterinarian to determine the best treatment.

Foals with Liver Failure

After a serious illness or injury, newborn foals can develop liver failure. Blood infections (septicemia), bacterial toxicities in the blood (endotoxemia), infectious disease (such as leptospirosis or equine herpesvirus 1, intestinal obstructions), suffocation, iron toxicity and malformations within the liver (called Biliary Atresia) are all possible causes of liver failure. Stomach ulcers, which are a condition that causes inflammation of the small intestine, can cause cholangiohepatitis. This is an inflammation of the bile vessels and surrounding tissue. Hemolysis and neonatal isoerythrolysis can also lead to liver disease. Intracavenous nutrition can cause liver disease by interfering with the flow and causing a blockage in the bile.


Hemochromatosis refers to a condition in which excessive iron is deposited within the liver cells. This can cause damage and dysfunction to the liver and other tissues. This disease in horses is thought to be caused by a dysfunctional liver that can’t properly metabolize iron. This disease is not inherited or caused by excessive iron intake in horses’ normal diet.

Weight loss, lethargy and loss of appetite are the most common symptoms. Certain liver enzymes are more prevalent in the blood. A enlarged liver is characterized by iron accumulation in the liver, lymph nodes and pancreas, pancreas and spleen, thyroid and kidneys, as well as glandular tissue and iron accumulation. A liver biopsy is performed to confirm the diagnosis. Horses with a history of iron excess should have a high iron level in their liver tissue. This confirms the diagnosis.

There is no cure for this condition, despite the existence of many treatment options and drugs.

Right Liver Lobe Atrophy

Young horses’ right lobe is the largest, but it often shrinks (atrophies in older animals) and becomes fibrous. Although the exact cause is unknown, researchers suggest that the condition could be caused by the long-term compression of right lobe by expanded intestines. This condition may be caused by horses being fed high-concentrate and low-fiber diets. Colic can be seen in certain cases of right lobe atrophy. Some horses may also have signs that are not related to their digestive system.

Torsion of the Liver Lobe

Horses can experience colic when the liver lobe twists. Sometimes, liver tissue may die. The liver might show higher enzymes and fibrinogen levels. The liver’s dead section may contain bacteria. Diagnostic surgery may be necessary.

Hepatic Amyloidosis

Amyloid is a misfolded protein. Amyloid can build up in many organs, causing tissue damage and impairment. Amyloidosis is most prevalent in horses’ livers and spleens. This condition can be caused by severe parasite infection, long-term infection, or inflammation. It is progressive and not treatable. (See also Amyloidosis In Horses).

Primary Hyperammonemia

Hyperammonemia is a condition that causes excessive levels of ammonia, a byproduct from protein metabolism, in the blood. Because the liver is unable to adequately remove ammonia from blood, hyperammonemia often occurs in the context of liver disease. Primary hyperammonemia is a condition in which horses have high blood ammonia levels, but they do not have liver disease. This condition can cause blindness and other severe neurologic symptoms. Although the cause of the condition is not known, it may be caused by an overgrowth in bacteria in your intestines. The symptoms are similar to certain types of liver disease but not directly related to it. Nearly all cases are associated with colic, intestinal disease, diarrhea and/or colic. Most cases of the syndrome are associated with diarrhea and colic, which can be seen between 24 and 48 hours before any neurologic signs. The results of blood tests showing increased blood glucose and ammonia levels, as well as low blood bicarbonate levels, are often used to diagnose the condition.

Most horses experience neurologic signs that resolve in 2 to 3 days. Supportive treatment is available (intravenous fluids; potassium chloride, glucose and sodium bicarbonate); as well as drugs to decrease ammonia absorption.

Morgan Weanlings have hyperammonemia

Morgan foals are susceptible to a syndrome of ill-health, high blood ammonia levels, and injury to the liver. Although the causes of the syndrome are unknown, affected foals may be related. Symptoms usually appear around weaning. Increased levels of liver enzymes and blood ammonia (which are indicators of inflammation in the liver) can be a sign that there is something wrong. Neurologic disease can improve with treatment but it will return once treatment is stopped. The disease can be fatal.

Portosystemic Shunts

Portosystemic Shunts are conditions where blood vessels bypass the liver. This causes toxins that would normally be removed by the liver to remain within the blood. This causes an increase in blood ammonia and nerve system signs.

The condition can be present from birth but is usually first noticed when foals reach about two months of age and begin to eat more grain and forage. The neurologic signs include wandering, depression, staggering, blindness, circling and seizures. Feedings are often associated with the most severe signs. Imaging techniques such as ultrasonography or contrast x-rays can often reveal the shunt.

Foals with a confirmed shunt may have surgery. However, the outlook is uncertain. Some foals may be controlled by limiting their intake of protein, managing their diet carefully, and using products that reduce ammonia production in the intestines. To reduce neurologic signs, support care may be required with fluids, potassium and dextrose. This disease can be controlled with great care by the owner.

Allison Price
Allison Price

I’m Allison, born and raised in San Diego California, the earliest memory I have with horses was at my grandfather’s farm. I used to sit at the stable as a kid and hang out with my Papa while he was training the horses. When I was invited to watch a horse riding competition, I got so fascinated with riding!