A comprehensive blood test can reveal internal imbalances or conditions that are not visible from the outside but still have a major impact on how your horse’s body uses nutrients. Below, we explain the key blood parameters your veterinarian examines and what each value can reveal about your horse’s health and weight.
Blood parameters your vet will review
Complete Blood Count (CBC)
A low red blood cell count (anemia) means less oxygen is transported to the muscles, causing fatigue and poor condition. A high white blood cell count indicates infection or inflammation, which diverts nutrients away from growth and recovery. Chronic inflammation can gradually cause weight loss, even when calorie intake is sufficient.
Total Protein and Albumin
Low values indicate poor protein absorption or a chronic condition. This can occur when the intestinal lining is damaged or inflamed, allowing proteins and albumin to leak out of the bloodstream. Horses with chronic diarrhea, gastric ulcers, or liver problems often show low values.
Globulin
High globulin levels may indicate prolonged inflammation or infection. Horses with elevated globulins often use more energy to fight disease and may lose weight despite eating well.
Liver Enzymes (AST, GGT, SDH)
Increased values signal liver stress or damage. An overworked liver cannot properly store or release energy, making a horse appear thin, lethargic, or generally unwell.
Kidney Values (Urea, Creatinine)
High levels suggest reduced kidney function or dehydration. Chronic kidney issues cause decreased appetite, muscle breakdown, and a dull coat. Affected horses may drink and urinate more while still losing weight.
Electrolytes
Imbalances can indicate dehydration or organ dysfunction. Long-term electrolyte disturbances reduce digestion and nutrient absorption. A shortage of sodium or chloride may cause fatigue and reduced appetite.
Glucose and Insulin
Glucose and insulin regulate energy levels and energy utilization. Abnormal values show that the body is not converting feed into usable energy effectively and may indicate metabolic or endocrine disorders such as Equine Metabolic Syndrome (EMS). Metabolic disorders can sometimes mask weight loss because they alter fat distribution.
Adrenocorticotropic Hormone (ACTH)
ACTH levels provide insight into pituitary gland activity. High values may indicate PPID (Cushing’s disease). Symptoms include topline muscle loss, a long or curly coat, increased drinking and urination, and delayed shedding. This condition is more common in older horses, though not exclusively (Barrelet & Ricketts, 2002; Charyberdiyev & Yoldashov, 2025).
Conclusion
A blood test provides deeper insight into your horse’s body and helps your veterinarian identify hidden problems that may explain persistent weight loss or poor condition. Whether the issue lies in the liver, kidneys, metabolism, or an underlying inflammatory process, the results help determine the next steps toward recovery. If the blood values are normal—or instead show low protein levels, liver abnormalities, or signs of chronic inflammation—your veterinarian may recommend a gastroscopy to confirm conditions such as gastric ulcers or intestinal disease.
Once the underlying cause has been identified, the focus shifts to nutrition and ration management. In our related blog post, you can read more about how to best feed an underweight horse and how to adapt the ration based on the specific cause.
