Everything a horse eats or drinks must pass through its liver. Despite the horse’s large size and long lifespan, its liver is proportionally small and tasked with an immense workload. Compared to many other animals, the equine liver is more frequently exposed to strain and potential harm from:
- Contaminants in feed and water
- Therapeutic substances such as wormers, antibiotics, steroids, and painkillers
- Natural toxins found in forage and while grazing
Because of this, it’s not surprising that liver function can sometimes become impaired. While usually not immediately life-threatening, even mild dysfunction may cause horses to underperform, become lethargic, or appear generally unwell. Some horses seem “always less than healthy” because certain liver functions are not operating at optimal levels.
One complication is that fluctuations in liver performance are not always detectable through routine tests and may be overlooked as a cause of poor performance or reduced wellbeing. Since horses lack a gall bladder, they cannot store bile. This means they rely entirely on their liver’s immediate function—making them more vulnerable to even minor or temporary dips in liver efficiency.
Key Functions of the Horse’s Liver
The liver carries out a vast array of essential roles, including:
- Filtering and removing toxins, including drugs and environmental poisons
- Producing bile for digestion
- Generating heat, vitamins A and D, heparin, plasma proteins (albumin, globulin), clotting factors (prothrombin, fibrinogen), uric acid, and urea
- Storing glycogen, fat, iron, and fat-soluble vitamins (A, D, E, K)
- Regulating blood glucose levels
- Metabolizing fats, proteins, and carbohydrates
- Producing cholesterol, phospholipids, and non-dietary essential amino acids
When Liver Function Declines
When the liver is damaged or overburdened, it may fail to filter toxins and metabolic by-products effectively. This buildup can compromise overall health and strain the kidneys. Fortunately, with timely care, the liver has a remarkable ability to recover—unless it has progressed to cirrhosis, where permanent scarring prevents normal function and may ultimately lead to liver failure.
The Workings of the Equine Liver
A healthy liver in a 15–17 hand horse produces between 2.4 and 3.5 litres of bile per day. Positioned between the gastrointestinal system and the systemic circulation, the liver is often described as the “antechamber of the heart.” It collects blood from the gastrointestinal tract and spleen via the portal vein, and directs it into systemic circulation through the right side of the heart.
Roughly 20% of the horse’s cardiac output passes each minute through the liver’s vascular system, which is made up of an extensive sinusoidal network.
The Metabolic Hub
Beyond its detoxification role, the liver governs multiple metabolic processes—proteins, fats, carbohydrates, minerals, and water—through its “metabolic pool.” During metabolism, harmful by-products are formed; the liver ensures these are neutralized or eliminated. For instance, in a diseased liver, ammonia (a normal waste product) can accumulate to harmful levels.
Other key roles include:
- Synthesizing albumin, crucial for maintaining blood volume and transport functions
- Supporting reticuloendothelial (RES) immune activity, even when damaged
The earliest signs of even mild liver dysfunction are often vague—such as reduced appetite or low energy. Toxic substances, drugs, heavy metals, and environmental poisons are all capable of causing damage.
Because the liver is so vital, even minor impairment can hinder its many interconnected functions. Recent research also highlights the liver’s role in inflammatory conditions, adding further to its importance in equine health.
Conclusion
The liver is essential to a horse’s overall health, performance, and resilience. Despite its remarkable capacity, there are limited remedies that can repair serious liver injury. However, with awareness, early detection, and appropriate support, the liver often has an excellent ability to recover and continue performing its critical tasks.
Disclaimer:
This publication is for informational purposes only and is not intended as veterinary advice. While every effort has been made to ensure accuracy, the information provided should not replace consultation with a qualified veterinarian. The authors, publishers, and distributors accept no liability for any loss, injury, or damage resulting from reliance on this information. Always seek professional veterinary guidance before making decisions regarding the health, nutrition, or treatment of your horse.