Liver values in horses: how to read your blood test results

Which liver values appear on the results?

A standard blood test in horses typically measures four liver enzymes: GGT (gamma-glutamyltransferase), GLDH (glutamate dehydrogenase), AST (aspartate aminotransferase), and SDH (sorbitol dehydrogenase). In addition, bilirubin and albumin are regularly included. GGT and GLDH are the most liver-specific values in horses. AST also rises with muscle damage, so your vet will always assess that value together with CK (creatine kinase). Each of these enzymes tells its own story: some point to acute cell damage, others to chronic conditions or bile stasis.

Reference values: what are the limits?

Reference values can vary slightly between laboratories, but the following ranges are widely used in Dutch equine practice:

• GGT: 10–80 U/L (higher values indicate liver damage or bile stasis)
• GLDH: 0–10 U/L (even mildly elevated is significant; strongly elevated = acute cell damage)
• AST: 150–400 U/L (also elevated with muscle problems)
• SDH: 0–8 U/L (highly liver-specific, rises quickly with cell death)
• Total bilirubin: 10–51 µmol/L (rises with fasting, haemolysis, or liver disease)
• Albumin: 25–38 g/L (low in chronic liver insufficiency)

What does an elevated GGT mean?

GGT is the most commonly requested liver value in horses and also the most sensitive. A value above 80 U/L always warrants attention. A mildly elevated GGT (80–200 U/L) can indicate a dietary error — too much protein or poor-quality roughage — but also an early stage of seneciosis (poisoning by ragwort). A GGT above 500 U/L almost certainly points to serious liver disease. Important: GGT declines slowly after recovery; it can take weeks for the value to normalise, even when the liver has already healed.

When is it sensible to repeat a blood test?

A single measurement gives you a snapshot. Only with repeated measurements can you see whether a value is rising, stable, or falling. For example: during an annual check-up, your horse has a GGT of 95 U/L. After six weeks on a modified diet, you test again. If the value has dropped to 60 U/L, the approach worked. If it has risen to 160 U/L, further investigation is needed. In the horse profile of EquiSight, you can save blood results and compare them over time, so you can see trends at a glance.

Causes of liver abnormalities in horses

• Seneciosis: chronic poisoning by ragwort in hay or pasture
• Hyperlipemia: accumulation of fats in the liver, particularly in ponies and donkeys
• Gallstones or bile stasis: rare but possible, visible through high GGT and bilirubin
• Liver abscess or tumour: AST and GGT strongly elevated, often also fever and weight loss
• Aflatoxins in mouldy feed: acutely dangerous, GLDH and SDH shoot up
• Primary liver insufficiency: albumin drops, horse becomes lethargic and loses weight

What do you do with the results in practice?

When you receive the results, don't just call to find out whether something is 'elevated' — also ask how significant the increase is and which combination of values is abnormal. GLDH and SDH both elevated together indicates acute cell damage and calls for prompt action. A mildly elevated GGT alone, without other abnormalities, can often be followed up first with dietary adjustments and monitoring. Use EquiCoach in EquiSight to explore the results: you enter the values and receive an explanation of their possible meaning and next steps, without having to wait for a callback appointment.

Diet and management with liver stress

When the liver is under stress, the approach centres primarily on feed. Reduce the protein content of the ration — a maximum of 10% crude protein in dry matter. Avoid grass silage and old, mouldy hay. Ensure sufficient exercise so that fat metabolism keeps moving. Do not add unnecessary supplements; the liver has to process those too. Check the pasture for ragwort and remove the plant including its root. Record all feed changes in the EquiSight calendar, so that at the next blood test you know exactly what has changed.