Elevated Liver Enzymes in Horses: How a Horse's Liver Could Become Compromised

When your horse is suddenly performing poorly or not acting like themselves, it can be hard to decipher what’s causing it.

The liver, along with everything that makes up the equine digestive system, can have a significant effect on a horse’s performance and health overall. Since ulcers are such a common occurrence, for example, many horse owners and trainers are aware how this one condition can have such a strong effect on a horse’s performance.  

However, elevated liver enzymes, or liver diseases, are also common and can cause their own set of issues that are oftentimes overlooked or misinterpreted. 

The Liver’s Importance and How it Could Become Compromised 

The liver is a vital organ for a number of a horses’ bodily processes, especially digestive processes, and holds about 10% of a horse’s blood supply. The liver's main function is to filter and remove toxins from the blood, while synthesizing proteins, secreting bile, and metabolizing fatty acids, fats, glycogen, sugar, and carbohydrates. 

Because the liver is cleansing the horse’s blood supply, it makes it very susceptible to contaminants, which can lead to diseases of the liver.  

In mature horses, liver disease is commonly caused by infection, exposure to toxins in plants or food, and even strenuous activities that can elevate certain liver enzymes. 

Liver Enzymes and Poor Athletic Performance in Horses

One of the most common causes of a compromised liver is one that is frequently seen in the Thoroughbred and Standardbred racing industries and is called Maladaptation to Training Syndrome, also known as High GGT Syndrome. It is characterized by an increase in a liver enzyme in a horse’s blood called y-Glutamyl-Transferase (GGT). 

The exact cause between poor performance and elevated GGT is unknown. However, a possible link could be the strenuous activities, such as intensive training and racing, lead to the accumulation of oxidative stress and free radicals in the horse’s body. 

There are studies that show an increase in GGT activity on training and racing days. Then, the GGT levels would return to normal when these strenuous activities stop or decrease. Because of this, chronically high GGT is believed to be caused by maladaptation to training. 

It is a common misconception that the high levels of GGT cause poor performance, rather they are an indicator of compromised health. After a decrease in training intensity, GGT levels return to normal and horse performance improves. 

Other Causes of Elevated Liver Enzymes in Horses

If other liver enzymes are also increased along with the GGT however, hepatic disease, such as viral hepatitis, is worth looking into, as well. Hepatitis, which is inflammation of the liver, is not as common, but can be caused by certain bacteria, parasitic migration through the liver, biliary obstruction, acute viral liver disease (Thieler’s Disease), and certain toxins.  

Another example of how a horse could compromise their liver is by eating a poisonous plant and ingesting a common toxin, like pyrrolizidine alkaloids, which are found in pastures and even in feed occasionally. 

Some of types of plants that could contain pyrrolizidine alkaloids are a part of the 17 species of Senecio family plants, such as Riddell’s Ragwort, or Prairie Ragwort. Switchgrass, Witchgrass, and Klein grass are also poisonous plant species. 

When these plants are ingested and pass through the liver, they kill or divide liver cells and can cause liver scarring. 

While horses typically find these plants unappetizing, and therefore, they naturally tend to avoid eating them, they can still be consumed under a few different conditions. If certain weather conditions occur, such as droughts, the horse might be more inclined to eat them. When hay is baled, it’s also likely some of these pyrrolizidine alkaloid plants will end up in their hay during the baling process as it’s hard to avoid them. 

Signs of Liver Insufficiency in Horses

Unfortunately, the signs of significant liver insufficiency are typically not evident until 60% - 80% of the liver is nonfunctional. 

Hepatic encephalopathy, which is a neurological issue that’s caused by poor liver function, can cause a number of symptoms. 

It’s important to understand that the early signs of liver insufficiency due to hepatic encephalopathy are vague, and often overlooked or mistaken for something else. These early signs could be diarrhea, constipation, decreased appetite, depression, lethargy, excessive yawning, head pressing, fever, circling, colic, lack of coordination, weight loss or overall abnormal behavior. 

Since a main function of the liver is to remove toxic substances from the horse’s blood, an increase of a toxin called phylloerythrin   that is present in the plants horses eat can cause a more intensive sensitivity to UV sunlight (photosensitization). When phylloerythrin is exposed to light after reaching the skin, it causes damage. This sensitivity to light is worse in lighter-skinned horses. Damage to the skin could present as reddening, excessive itching, edema under the skin, ulceration, and peeling. 

Jaundice, another skin change, is a yellowing of the gums, skin, and whites of the eyes and is a tell-tale sign something is not right with the horse’s liver. 

While liver disease is common in horses, fortunately, liver failure is uncommon. Since a horse’s liver helps produce clotting proteins, a more severe liver failure in horses could even lead to secondary bleeding issues. A harsher, abnormally loud, or high-pitched breathing sound could also be a symptom for horses with liver failure.

The best way to identify if liver disease is present in your horse is through routine blood screening to check for any elevation in the liver enzymes that indicate liver problems. 

Your veterinarian will likely recommend an ultrasound or even a liver biopsy to confirm or see how progressed the disease is. 

Why This Isn’t a Horse Diet Related Issue

It’s easy to assume that liver related diseases could be a diet related issue. 

In years past, it was believed that nutritional management, such as feeding a high starch, low oil, and low protein diet, would significantly affect horses with liver disease for the better. 

But today, thanks to further studies, data, and research, we now know there is little benefit to these dramatic diet changes. In fact, horses with liver diseases no longer receive these extreme dietary changes from veterinarians unless their current diet is much higher in protein and starch than what is typically recommended. 

As with all horses, a forage-first diet that is fed throughout the day is always important for overall horse health. 

Feeding a horse feed that has balanced nutrition with the appropriate levels of sugar, starch, protein, fat, vitamins, minerals, etc. such as Kalm N’ EZ® Pellets, is also important for keeping all your horse’s organs functioning at their best. 

Being mindful of the types of toxic plants in your area, tracking your horse’s performance during training and competitions, and being mindful of the early signs of liver insufficiency could help with prevention or an early diagnosis of some of these common liver diseases. 

Need help putting together a diet for a horse with any of the above live-related diseases? Our team would love to help!

Article By: Sarah Welk Baynum
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