An Irish draught gelding has been hailed a “special hero” after he helped save the life of a critically ill pony who urgently needed a blood transfusion.

Coral, a 9.2hh mare who was taken in by Redwings as part of a welfare case, was losing weight. Staff noticed redworm larvae in her faeces, and she went “downhill quickly”.

“Coral was losing protein from her intestines. It was a critical situation, and we could have lost her,” said Dawn Trayhorn, the Redwings vet who oversaw Coral’s care.

Fellow Redwings resident Rourke, a healthy 17hh gelding, stepped forward as the “perfect” plasma donor for Coral.

“She wouldn’t have survived without the intensive care she was given, and the plasma from Rourke was vital in getting her to turn the corner,” said Dawn.

“Rourke did really well during the procedure and had lots of TLC and yummy dinners afterwards. He’s a real animal hero.”

Dawn said Coral is now “doing great”.

“She’s back at Redwings’ Caldecott visitor centre and hopefully can be rehomed at some point in future,” she said.

“It’s amazing when we’re able to save a life. The whole team pulls together in situations like this. It’s difficult, but also what we’re here for. Coral and Rourke are very special to us.”

To donate plasma from one horse to another, blood is taken from the donor and the plasma drawn from it. Plasma contains white blood cells and antibodies used for fighting infections. Plasma transfusions can also be used for newborn foals, who have not received adequate colostrum.

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There are many reasons why your vet might recommend taking a blood test. Gil Riley MRCVS looks at what these tests reveal — and why they can form a useful piece of the health check puzzle

Blood tests can be very helpful in assessing the health status of a horse as an addition to a full clinical examination.

In some cases, blood tests can provide an exact diagnosis. It is much more usual, however, that the test acts as an aid to diagnosis, with results being considered alongside other findings. To understand why your vet might take a test, it’s helpful to understand the basics of blood.

What is blood?

A horse’s blood is made up of approximately 60% water and 39% red blood cells. The remaining 1% comprises white blood cells (WBC) and thousands of elements, electrolytes, enzymes and proteins.

Each individual red blood cell contains haemoglobin. This protein-iron complex gives blood its red colour and is the substance responsible for carrying oxygen around the body.

For every 100 red blood cells, there is roughly 1 white blood cell, the chief role of which is to fight infection. Other functions of the blood system are to carry clotting factors and repair cells to the site of damaged tissue; protein components of the immune system to where there is an infectious challenge, and nutrients from the gastrointestinal tract to the rest of the body.

In a healthy horse, these blood components are regulated and maintained in a way that varies only slightly between individuals — so the different components are largely consistent. This means we have a clear reference range for what is normal — but this changes when disease is present.

So because of this “predictability” of blood, a blood test can be a vital tool in identifying disease.

Types of blood test

These are generally divided into 4 main groups:

1. Haematology. This is the name for the examination of a horse’s red and white blood cells. The packed cell volume test, or PCV, reveals the percentage of blood volume comprised of red blood cells. A low number could indicate anaemia, often the result of other disease, including worm infestation. An increased PCV can indicate dehydration, among other possibilities.

Looking at the total number of white blood cells can help diagnose various types of inflammation. This number typically decreases with severe, acute inflammation and increases with slow-developing or chronic inflammation. Variations in the number of white blood cells present can help differentiate between say allergic-type inflammation or a viral illness.

The white blood cell count (WBC) is also useful in determining whether or not a condition is responding to treatment. The WBC number would increase with a mild to moderate bacterial infection, such as pneumonia, for example, but would decrease towards the normal range with treatment by an appropriate antibiotic. Specific white blood cells such as neutrophils are also examined for changes in cellular structure associated with illness.

With WBC counts, it is often beneficial to perform successive blood tests a few days to a fortnight apart, depending on the condition. A trend in any changes can then be identified.

2. Biochemistry. This is the study of the non-cellular component of blood. When a blood sample is collected and allowed to clot, all red and white cells, along with platelets (these help the blood to clot) and clotting proteins themselves, are removed.

The remaining “serum”, which is composed of water plus numerous products such as elements, electrolytes and enzymes, can offer many clues. Measurement of electrolytes can be helpful. Abnormal levels of electrolytes such as sodium, potassium or phosphorus can cause problems ranging from neurological disorders to kidney dysfunction or an abnormally low heart rate (bradycardia).

Serum proteins and inflammatory markers can also be usefully tested. Varying levels can indicate gastrointestinal disorders and some forms of cancer, as well as other problems including infection, such as lung abscesses in foals.

Analysing blood for specific antibodies is vital in identifying infectious diseases such as strangles. Although it is not a direct test for the presence of the infectious agent, it tells us indirectly that the body has mounted an immune response to the agent and has therefore been exposed to it. Sampling at a later date can then reveal if immunity is fading and therefore whether the challenge (disease) affected the horse recently or at an earlier date.

Serology, which includes measuring antibodies, is commonly used to identify viral illnesses including herpes. Biochemistry may also be used to measure enzymes, the proteins that can serve as important markers for identifying tissue damage. When the liver is damaged, for example, certain enzymes present in large quantities in the liver tissue will show high readings in the serum.

3. Endocrinology. Tests can be performed to measure hormone levels in the blood. There is now a reliable test for the hormone ACTH, which is excreted in excessive amounts by the pituitary gland when a horse is suffering from Cushing’s disease. Fortunately, an effective treatment is now available, so the ability to diagnose the condition quickly and easily with a specific blood test is a real breakthrough.

Endocrinology can also help in the diagnosis of equine metabolic syndrome, which is commonly seen in overweight ponies.

Rigs (males with either one or both testicles retained in the abdomen) can be identified with a recently developed and accurate blood test for the anti-mullerian hormone (AMH), which is excreted in large amounts by abdominally situated testicles. The same test is also useful for identifying mares suffering from a granulosal cell tumour, the most common tumour of the ovaries.

4. Genetic testing. Blood tests are commonly performed by breed societies to confirm parentage of a foal. Specific genetic markers can determine the foal’s DNA make-up and detect some inherited diseases too.

Regular screening

While blood tests are typically taken in response to a health problem, regular screening may be recommended by your vet in some cases.

An older horse is more prone to declining organ function and a regular (annual, at least) blood test can help determine whether any supportive treatment, care or dietary change is appropriate. Dosing long-term with an anti-inflammatory such as bute can affect gut lining and kidney function. A regular blood test will detect any damage at an early stage so the dose can be reduced or an alternative medication used.

Many competition horses have a routine haematology and biochemistry test to ensure they are in peak physical condition. As with human athletes, prime physical fitness involves levels of exercise that stress the body and render it more vulnerable to infection. Routines can then be adjusted if tests reveal a stressed or challenged immune system.

For a normal, healthy horse under a less rigorous workload, a routine blood test for general health is probably unnecessary. Providing the horse appears in good condition, such a test is unlikely to throw up any new information.

5 blood test facts

1. A test produces a snapshot of what’s happening in the blood when the sample is taken

2. Repeat testing can reveal trends or provide a means of assessing response to treatment

3. The results are just part of the picture when it comes to reaching an accurate diagnosis

4. Some conditions produce no measurable blood changes. These include gastric ulcers, lameness, tooth pain and most colics and skin conditions

5. Horses can be blood-tested to check for the presence of tapeworm, as well as other specific infections and diseases

Blood in numbers

54

the average amount of blood, in litres, in an adult horse

100

the approximate number of red blood cells for every one white

60

the percentage of blood made up of water

5

types of white blood cells: neutrophils, lymphocytes, monocytes, eosinophils

This veterinary clinic feature was first published in Horse & Hound magazine (3 January, 2014)

The life of a four-day-old foal has been saved by a blood transfusion from a horse rescued by the Blue Cross.

The warmblood colt named Conker had been diagnosed with a fatal foal disease known as neonatal isoerythrolysis, which is similar to Rhesus syndrome in babies. The condition is caused by antibodies absorbed from the mare destroying the foal’s red blood cells during pregnancy.

When vets at Pool House Equine Clinic in Lichfield saw Conker they knew he urgently required a blood transfusion. Luckily, Blue Cross Harold (picture below left), a 15-year-old gelding who had been placed on loan to practice vet Richard Stephenson, was on hand to provide the life-saving fluid.

Harold stood patiently for over an hour while three litres of blood were collected and transfused into the sickly foal, literally breathing life back into his veins.

“The effect was like a miracle,” said Richard Stephenson, who treats horses at The Blue Cross equine centre in nearby Rolleston-on-Dove.

“Conker went from collapsed and lethargic to lively and energetic in less than an hour. By the end of the transfusion we had to sedate him to keep him still!”

Blood tests after the procedure confirmed that the foal’s red blood cell count had doubled to a safe level. He was closely monitored over the next 10 days and went on to make a full recovery.

“Without Blue Cross Harold we would certainly have lost the foal,” said Richard. “Fortunately he has the perfect, laid-back temperament to cope with being a blood donor.

He stood perfectly for over an hour while we took the life-saving blood and afterwards behaved as though nothing unusual had happened.”

Kath Urwin, manager of The Blue Cross Rolleston centre said: “All the staff at The Blue Cross are so proud of Harold.

“When we placed him on loan to the vet practice we never imagined he could end up saving another horse’s life. And as a rescue horse himself, it’s lovely to think that he was able to help little Conker.”

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Finding a horse standing in a large pool of blood, whether from a wound, a nosebleed or after foaling, is every owner’s nightmare. In many cases, the amount of blood looks more than it is and, as the horse is adapted to cope with some bleeding, this should not be a problem.

However, a wound involving a major blood vessel, blood loss during surgery and severe bleeding from a tumour can be life threatening. Rapid bleeding reduces the volume of blood in the horse’s circulation and limits its ability to deliver oxygen to the body’s tissues.

If your horse has lost a lot of blood in a short time, an emergency blood transfusion may be essential. The vet must take care to avoid adverse reactions to the transfusion, such as an allergic response.

The major benefits of a blood transfusion only last for a few days, but the new blood will provide immediate help to the horse and allow time for its own bone marrow to respond and produce a fresh supply of healthy red cells during the following few weeks.

A newborn foal suffering from haemolytic anaemia, in which the foal’s red blood cells are destroyed by antibodies absorbed from its mother’s colostrum, will also need a blood transfusion. Haemolytic anaemia occurs when the foal inherits a red cell type from its sire, which is different from its dam’s blood group. The disease can cause severe anaemia, despite there being no visible blood loss.

Blood donor

A suitable horse must be selected as the blood donor for the transfusion to minimise the chances of unfavourable side effects. The surface membranes of horses’ red cells are covered with numerous “antigens” which are used to classify horse blood into eight groups.

If red cells from a donor horse of a different blood group are added to a patient’s circulation, the patient recognises the foreign antigens and produces antibodies against the new red cells.

Generally, it is safe to give a first transfusion to a patient who has not previously received blood, even if the donor and patient are not of the same blood group. This is fortunate, as the first transfusion is frequently carried out during an emergency where there is no time to carry out a detailed cross-match.

However, if a second transfusion is performed more than a week later, the donor and recipient blood types must be matched carefully to prevent serious allergic transfusion reactions.

Plasma Transfusion

Other components of blood, such as plasma, can also be given as a transfusion. Newborn foals who do not suckle sufficient colostrum, which contains a rich supply of essential antibodies to help fight everyday bacteria, are at risk of developing life-threatening infections.

Foals can only absorb these desirable antibodies from the colostrum during the first few hours of life and, if their blood level of antibodies is low, the most efficient way to boost the levels is by a plasma transfusion.

Plasma can either be obtained by the vet taking blood from the mare and removing the red cells to collect the antibody-rich plasma, or using a commercially available plasma. The commercial plasma bags can be stored frozen so that they are always available.

Newborn foals which have not received adequate colostrum usually need about 1litre of plasma to improve their antibody status, but the vet needs to carry out follow-up blood tests to check this is sufficient.

If the foal is already sick, a larger volume of plasma may be needed to combat the effects of dehydration, infection and lack of its own immunity to disease.

This feature was originally published in Horse & Hound

Most horseowners are familiar with the concept of blood testing, but how much do you really know about blood and how and when it can be used to diagnose disease in horses?

Blood is a liquid tissue composed of a solution of electrolytes (salts) containing cells and proteins. It has a variety of functions, from transporting oxygen, carbon dioxide, nutrients, hormones and many other substances around the body to regulation of the body’s temperature.

To understand its functions, we need to look at the major components of equine blood separately.

Blood cells

There are three main types of cells in blood:

• red blood cells (RBCs or erythrocytes)
• white blood cells (WBCs or leucocytes)
• platelets (karyocytes)

Red blood cells are the most common cells. They are fairly simple cells whose principle role is to transport oxygen from the lungs to the tissues and to take carbon dioxide from the tissues to the lungs.

As oxygen is soluble in blood, why are RBCs necessary? If oxygen was only carried in solution in the blood, the amount of blood needed to be pumped around the body would be impossibly high. Instead oxygen is transported via a carrier molecule, called haemoglobin. When oxygen is attached to haemoglobin, blood can carry many times more oxygen than would be possible in solution.

White blood cells form a part of the immune system. They are far less numerous than RBCs. There are five major types of WBC: neutrophils, lymphocytes, eosinophils, monocytes and basophils – each performing a different function.

Platelets are a smaller type of cell which are involved in the clotting mechanism that repairs damaged blood vessels.

The fluid part of blood is known as plasma. It is a complex solution of electrolytes (salts), the ones present in the largest quantities being sodium and chloride. The plasma also contains proteins, which have a range of functions, including the maintenance of blood volume and the transport of many of the substances carried by blood. Specific plasma proteins include antibodies and clotting factors.

What can blood tell us?

Since blood has an intimate role in the metabolism of most body tissues, changes in its composition can be a very effective way to diagnose disease.

It is important that clinicians using blood test results do not interpret them in isolation, but in the light of the overall clinical features of the case. All of the components of blood can hold useful information for the diagnosis of disease.

Variations in the number of white blood cells can give us important clues, among other things, as to whether an inflammatory process is present in the patient.

While you might expect the response to infection and other forms of inflammation to be an increase in the WBC count, this is not always the case. The WBC count and the proportion of the different types of WBCs varies according to the nature and duration of the patient’s disorder.

A common misconception is that it is possible to definitively distinguish between viral and bacterial infections on the basis of the proportion of white blood cells present in a sample.

It is important to remember that while the analysis of blood is a useful aid to the diagnosis of disease, it is no substitute for a full clinical examination.

The results of blood tests must be interpreted in the light of the clinician’s other findings about the patient’s health in order to arrive at as accurate a diagnosis as possible.

In other words, analysis of blood can be a very helpful diagnostic aid for the veterinarian, but it is not a magic test that always provides simple answers.