What Do My Horse’s Blood Values Mean? How a veterinarian interprets them

A comprehensive blood test can reveal internal imbalances that never show up from the outside, yet still shape how your horse's body uses and stores nutrients. Below, we walk through the blood parameters your veterinarian checks first in a weight-loss workup, and what each one can tell you.

Blood parameters your vet will review

Complete Blood Count (CBC)

A low red blood cell count, or anemia, means less oxygen reaches the muscles. The horse tires faster and holds condition poorly. A high white blood cell count points to infection or inflammation, and the body redirects energy toward fighting that instead of toward growth or recovery. Neutrophilia is in fact the single most common blood abnormality found in horses with chronic gut disease [1]. Left unaddressed, that kind of chronic inflammation causes weight loss on its own, even on a full ration.

Total Protein and Albumin

Low total protein and albumin usually point to poor absorption or a chronic underlying problem. When the intestinal lining is damaged or inflamed, protein leaks straight out of the bloodstream instead of reaching the tissues that need it. Horses with chronic diarrhea, gastric ulcers, or liver disease often show this pattern. In severe cases such as right dorsal colitis, plasma protein can fall below 5.0 g/dL and albumin below 1.5 g/dL [1].

Globulin

High globulin levels suggest prolonged inflammation or infection. The immune system runs at a higher energy cost when it's fighting something in the background, and that energy has to come from somewhere else. Close to half of horses with liver failure show a raised globulin count [1], which is why vets read albumin and globulin together rather than on their own. A horse can lose weight quietly this way, despite eating well.

Liver Enzymes (AST, GGT, SDH)

Raised liver enzymes signal stress or damage to that organ. GGT is considered the most reliable marker of equine liver disease. In one case series it was elevated in every one of 50 horses with confirmed liver disease [2]. AST and ALP tend to climb with chronic damage, while SDH and GGT rise faster and point to something more active [2]. An overworked liver can't store or release energy the way it should, and the horse ends up looking thin, dull, or simply off, even when nothing else seems wrong.

Kidney Values (Urea, Creatinine)

High urea or creatinine suggest reduced kidney function or dehydration. Chronic kidney disease brings decreased appetite, muscle wasting, and a dull coat. Some affected horses drink and urinate more, all while still losing weight.

Electrolytes

Electrolyte imbalances can point to dehydration or organ dysfunction. Left uncorrected for long enough, they interfere with digestion and nutrient absorption. A shortage of sodium or chloride in particular brings on fatigue and a flat appetite.

Glucose and Insulin

Glucose and insulin govern how efficiently the body turns feed into usable energy. Abnormal readings can point to a metabolic or endocrine disorder such as Equine Metabolic Syndrome (EMS), where insulin dysregulation is the defining feature [3]. No single test catches every case, so vets often pair a resting sample with a dynamic test such as the oral sugar test [3]. EMS can also mask weight loss rather than cause it outright, because it shifts where fat sits on the body instead of removing it.

Adrenocorticotropic Hormone (ACTH)

ACTH reflects how active the pituitary gland is. A high result may point to PPID, better known as equine Cushing's disease, which shows up as topline muscle loss, a long or curly coat, increased drinking and urination, and shedding that runs late. It's more common in older horses, though not exclusively [5]. Because a single ACTH reading has real limits as a stand-alone test [4], vets weigh it alongside the clinical picture rather than reading it in isolation.

Conclusion

A blood test gives your veterinarian a window into what's happening beneath the surface, and it often explains persistent weight loss or poor condition that has no obvious cause. Whether the issue sits in the liver, the kidneys, the metabolism, or a low-grade inflammatory process, the results point toward the next step. If the values come back normal, or instead show low protein, liver abnormalities, or signs of chronic inflammation, your veterinarian may recommend a gastroscopy next to check for gastric ulcers or intestinal disease.

Once the underlying cause is identified, the focus shifts to nutrition and ration management. In our related blog post, you can read more about how to feed an underweight horse and how to adapt the ration to the specific cause behind the weight loss.