By Clyde Vet Group

Blood tests have formed part of the investigation of a large number of illnesses, diseases and injuries for a long time in horses.

The number of tests available is continuously expanding and their accuracy improving, making analysis of blood a very useful diagnostic tool. Sometimes blood results will yield a diagnosis and in other situations the information they provide helps to build an overall picture of what may be going on. Taking blood is well tolerated by most horses and is generally a safe procedure.

Common uses of blood testing

1. Investigating illness. Many conditions will affect red and white blood cells, or circulating chemicals and enzymes. Blood tests can help differentiate diseases with similar clinical signs, thus ruling problems in or out, and, help reach a diagnosis.

2. Monitoring response to treatment after diagnosing an illness, the response to treatment can be monitored by repeating the tests, to ensure that the condition is being treated effectively.

3. Screening normal healthy animals can be screened to pick up early signs of a problem. This is particularly useful in older animals or those which may have been exposed to a contagious disease but might not yet have developed any clinical signs.

4. Pre-purchase examination (PPE). Blood samples are collected at the time of the PPE then posted and stored in a special facility for six months. If a problem such as lameness arises after purchase then the sample can be tested for a wide range of substances including pain-killing drugs and sedatives. In certain circumstances these tests may be performed immediately following the examination and it’s important to tell the vet if the results are required quickly.

5. Confirming exposure to infectious diseases. Exposure to diseases such as Equine Influenza and Streptococcus equi equi (Strangles) can be confirmed or ruled out. Some yards will request this for new liveries prior to their arrival. Also, prior to breeding, blood tests may be necessary as certain infectious diseases are sexually transmitted and can affect mare and stallion fertility, as well as causing illness.

6. Confirming the health status of an animal before export or import. Entry into many countries is dependent upon a clear disease screen. Blood tests are used to rule out serious infectious diseases and maintain the disease-free status of a country. The requirements will vary dependent on the countries involved.

7. Monitoring a patient during a general anaesthetic. Blood samples can be used to monitor parameters relating to patient safety such as oxygen and carbon dioxide levels whilst under anaesthetic.

8. Identification of banned substances. Professional equestrian competitions, including racing, monitor equine athletes for the presence of prohibited, performance enhancing drugs in the urine and blood to ensure a level playing field.

What do we measure?

1. Blood cells. The number and concentration of red blood cells, along with several types of white blood cells can be measured. This helps assess whether disease or illness is present, as well as the severity.

2. Blood chemicals

A. Enzymes/proteins Injured, inflamed or diseased organs and tissue will release many different chemicals into the bloodstream. Any rise or fall from normal levels can be measured and may be used to determine the nature, extent and severity of a disease process.

B. Hormones. Many different hormones can now be measured. One of the most common things we test for is a hormone called adrenocorticotrophic hormone (ACTH), the levels of which will be elevated in animals with pars pituitary intermedia dysfunction (PPID), also known as Cushing’s disease. Other hormonal tests include anti-mullerian hormone (AMH) to identify rigs, i.e. a male horse with hidden testicle(s), and certain ovarian tumours in mares.

C. Pharmaceuticals. During PPE (vettings) and among competition horses, drugs such as painkillers, anti-inflammatories, tranquillisers and other performance enhancers can be detected, even at very low levels.

D. Antibodies. A horse will produce antibodies as part of the immune system’s response to an infection caused by a virus or bacteria. We can test for the presence of specific antibodies against many pathogens including streptococcus equi equi (Strangles), Equine Viral Arteritis (EVA) and Equine Herpes Virus (EHV) to name but a few.

E. Bacteria and viruses. As well as detecting antibodies or the horse’s immune response, certain infections can be confirmed by identifying the actual organism or it’s DNA.

As you can see there is a wide range of circumstances where blood testing is necessary or useful. Speak to your vet if you think a blood test may be useful for your horse