It’s in the blood

It’s in the blood

By Wendy Talbot on 23 April 2020

Whether animal or human, blood is essential. It’s an ingenious transport system, transferring oxygen from the lungs to all the organs and tissues in the body. Blood also moves nutrients, hormones and waste products around your horse’s body, where they can be absorbed or expelled, transports white blood cells and antibodies to fight infection and helps to control your horse’s temperature.

Blood tests are an important diagnostic tool because the blood can show how well certain organs are working and reveal early signs of some diseases.

What is blood made from?

Blood is made up of red blood cells, which give the blood its rich colour, white blood cells, platelets and plasma.

Red blood cells contain haemoglobin which enables cells to distribute oxygen around the body and remove carbon dioxide. Red blood cells are made in the horse’s bone marrow and released into the bloodstream. They are also stored in the spleen.

White blood cells are a part of the immune system and have the primary job of fighting infection. They do this in various ways such as by causing inflammation, generating antibodies and attacking viruses and germs.

Platelets have the sole role of forming clots to stem bleeding and are activated when there is an injury.

Plasma is largely water but also contains substances such as proteins, hormones, antibodies, enzymes, glucose, fat particles and salts. When a blood sample is taken the cells and certain plasma proteins clump together into a clot. The remaining fluid is called serum.

What can blood tests reveal?

Blood samples are very useful for monitoring health and detecting disease. While testing a blood sample can never replace a full veterinary examination it can provide important information to help diagnose a problem.

The results of an individual blood test are usually compared with normal ranges taken from horses of a similar age and type. Tests are logically grouped into profiles relating to the particular investigation.

A standard profile for a performance horse might include a complete blood count, inflammatory proteins and muscle enzymes. The results can help to identify horses with compromised health that may not be performing to their optimum potential.

Other abnormalities a blood test can detect include:

  • Inflammation – indicated by an increase in white cells.
  • Anaemia – diagnosed by a decrease in red blood cells. In horses this is most likely to suggest an underlying disease process such as infection as opposed iron deficiency.
  • Damage to the gut or kidneys or in some cases malnutrition may be revealed by low protein in the blood.

Instant results

Some vets can offer a point-of-care diagnostic blood test that can provide critical information related to equine inflammation in 10 minutes. A special hand-held reader can detect and quantify the biomarker Serum Amyloid A (SAA), a major, acute phase protein produced by the liver that rapidly and dramatically increases in response to inflammation. By measuring SAA, vets can assess the severity of an infection more quickly, often before clinical symptoms start and are able to monitor the horse’s response over the course of treatment.

Did you know?

The average 550kg horse has around 55 litres of blood (12.3 gallons).

Hot blooded horses such as the Thoroughbred have more around 15 ml more blood per kilo of bodyweight than cold bloods such as the Percheron.

A 550kg horse may lose up to 10% of its blood before showing signs of shock from blood loss.


Barrelet A. What can a blood sample tell us?

Absolute Horse August 2011

Accessed 22 March 2020

Ball M. Facts about blood

Accessed 24 March 2020

No specified author. Your horse’s blood

Accessed 24 March 2020

Nolen-Walston R. How to Interpret Serum Amyloid A Concentrations. In Proceedings: American Association of Equine Practitioners. 2015:130-137.




Wendy graduated from Bristol University in 1999. She then went on to complete a residency at Liverpool University and holds a European Diploma in Equine Internal Medicine. After working in practice for 13 years, she joined Zoetis in 2012 as the National Equine Veterinary Manager.

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