Hepatitis in Horses

Courtnee Morton, DVM
By Courtnee Morton, DVM on Jun. 24, 2022
Red mare and foal on green pasture

In This Article


What is Hepatitis in Horses?

Hepatitis is inflammation of the liver. The disease is not commonly encountered in horses, but mild cases may be under-diagnosed because clinical signs can be vague, and often don’t show until approximately 80% of the liver is affected.

Symptoms of Hepatitis in Horses

If you notice any of the following symptoms in your horse, call your veterinarian to schedule an appointment:

  • Anorexia (decreased appetite), or colic

  • Depression

  • Jaundice (yellowing) of the gums or eyes

  • Weight loss

  • Photosensitivity

  • Diarrhea or constipation

  • Abnormal bleeding or clotting, due to decreased clotting protein production in the liver

  • Neurological signs (head pressing, circling) in horses with low blood sugar or hepatic encephalopathy (HE)

If neurological signs are present, an emergency visit or trip to the nearby equine hospital is warranted. Increased ammonia can circulate in the blood from liver damage, or from ingested toxins that bypass the liver because it cannot properly perform its job of detoxification. Increased ammonia in the blood reaches the brain and can cause the above neurological signs.

Causes of Hepatitis in Horses

There are several potential causes of hepatitis in horses, including:

Acute Viral Liver Disease (aka Theiler’s Disease, Idiopathic Liver Disease, Serum Sickness)

A large portion of cases have a suspect relation to the administration of an equine-origin biologic (such as the tetanus antitoxin or equine plasma) 1-3 months prior to the onset of clinical signs. Not all horses will have this history, however. Signs progress rapidly, in less than a week, and can be fatal.

Equine Hepacivirus and Equine Parvovirus-Hepatitis can cause acute inflammation, or no clinical signs at all, with only elevated liver enzymes for a few weeks.


Clostridium bacteria is the most common genus. C. piliforme can cause Tyzzer’s Disease in foals younger than 6 weeks old. Foals may suddenly die with no clinical signs, as the disease progresses quickly. If caught in time, however, treatment can be successful.

Bacterial hepatitis is uncommon in adult horses. In these rare cases, C. novyi type B is the largest culprit, an organism that lives in the ground. After death, a horse’s body will turn black and bloated very quickly.


Parasitic migration through the liver can cause an inflammatory response. It can also cause blockage of the biliary duct.


Many plants can be hepatotoxic (damaging to the liver), especially pyrrolizidine alkaloid-containing plants; but most, unless ingested chronically or in large quantities, will rarely lead to liver failure. Some common hepatotoxic plants include:

  • Coffeeweed

  • Lantana

  • Ryegrass

  • Blue green algae

  • Sneezeweed

  • Tansy (common ragwort)

  • Groundsel

  • Tarweed

Biliary Obstruction

Cholelithiasis (buildup of calculi in the biliary tract), liver lobe torsion, large colon displacement, or parasitic obstruction of the bile duct can all cause inflammation of the liver and abdominal pain. Luckily, these are not common occurrences.

How Veterinarians Diagnose Hepatitis in Horses

A CBC and chemistry profile can reveal increased white blood cell counts in the presence of infection, and elevated liver enzymes, which indicates liver disease. Additional testing may include ultrasound imaging, which can be useful to see size changes or abscesses in the surface of the liver, or dilated bile ducts.

To determine the exact cause of liver disease, a liver biopsy is the definitive method. A needle will be passed into the liver and a sample collected to examine under the microscope. This can be safely done using ultrasound guidance.

Treatment of Hepatitis in Horses

If damage to the liver isn’t severe, providing supportive care will allow the liver time to regenerate and prevent fibrosis (scar tissue). Supportive care might include anti-inflammatories (Banamine), antioxidants or vitamins, and antibiotics if the disease is bacterial in nature. In horses with significant depression and anorexia, IV fluids supplemented with dextrose may be used.

If your horse is experiencing hepatic encephalopathy, these supportive measures will be more intensive. IV fluids with dextrose will be necessary to keep hydration and blood sugar values adequate. Your horse may be started on lactulose to decrease ammonia absorption in the intestines, and antibiotics such as Metronidazole will help decrease the amount of ammonia-producing bacteria in the gut. It will be important to keep the horse in a calm, somewhat dark area to minimize photosensitization.

Recovery and Management of Hepatitis in Horses

Your horse will need to avoid extended sun exposure during recovery. The focus during this time wil be proper nutrition intake. Your veterinarian may recommend smaller, more frequent meals. Untreated hepatitis can lead to hepatic encephalopathy (HE), which is a severe neurological disease. Horses with HE may become unsafe to handle, so be cautious and call your veterinarian if any of these signs are observed.

Prevention of Hepatitis in Horses

Luckily, hepatitis is not a common disease in horses. Some companies are beginning to test for Equine Hepacivirus and Equine Parvovirus-Hepatitis in horses used for biological products. Mares at postpartum that are administered tetanus antitoxin seem to be more susceptible to developing acute liver disease; giving your mare her full set of yearly vaccines 4-6 weeks before her foaling date can help prevent that.

Maintaining healthy pastures free of hepatotoxic and pyrrolizidine alkaloid-containing plants, and routine deworming of your horses will prevent toxic or parasitic liver issues.

Hepatitis in Horses FAQs

Can horses recover from liver damage?

Yes, if the damage is not severe or chronic (causing significant fibrosis), the liver can regenerate in time.

Is hepatitis contagious?

It is unclear if some viral causes of hepatitis are contagious, as they can occur in groups. The majority of causes are non-contagious, and more related to environmental factors (toxic plants, biologic products, etc.).

Featured Image: iStock.com/Callipso

Courtnee Morton, DVM


Courtnee Morton, DVM


Dr. Courtnee Morton is a 2017 Ross University School of Veterinary Medicine graduate. Since graduation, she completed an equine internship...

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