Understanding investigation techniques

While a detailed clinical examination can allow a vet to determine a lot of information about what is wrong with an ill or lame horse, further investigation is often needed to clarify the details of the horse’s condition, including the source of the problem. This will help the vet to determine the best treatment and advise the owner on the horse’s chances of making a full recovery.

Blood tests

Blood tests can pick up signs of infection, blood disorders, hormonal, liver, kidney, bowel, bone and heart problems, as well as conditions such as azoturia. They also aid assessment of severity and prognosis and can be used to monitor long-term conditions or to check response to treatment.

In most blood tests, a vet takes a sample from the jugular vein in the neck, which is then examined at a lab. Routine blood-screening tests comprise haematology, biochemistry and electrolyte components, the first allowing assessment of red and white blood cell numbers and function, and the others comprising tests for levels of enzymes, proteins and salts that give an indication about a range of diseases.

Blood tests can be taken at home or at a referral lab, with results available the same day or within a few days. Blood tests usually cost £30-£150, depending on number of tests, but complex tests, such as for hormonal diseases, can cost more.

Biopsies

Biopsies (tissue analysis) and tests on body fluids can allow identification of abnormal cells, and are indicators of inflammation and infection. Biopsies and fluid samples are often collected endoscopically or via a needle using ultrasound images for guidance. Because of the need for ultrasound, biopsies are usually done at a referral lab with results available the same day or within a few days. Examination of tissue samples costs around £50-100, plus cost of the ultrasound.

Endoscopy

Endoscopy is used with respiratory problems, and to evaluate the sinuses and internal organs, such as the oesophagus (particularly useful in horses prone to choke), stomach (for example, to check for ulcers), or bladder. It involves inserting a fibre-optic tube containing a camera into the horse, which allows the vet to see what is at the tip of the tube through a small eyepiece, or on a TV screen.

For respiratory problems, an endoscope is inserted up the horse’s nose, either while it is at rest, or while it is exercising on a treadmill, so that the inner surfaces of the trachea and nasal passages can be evaluated. Samples of discharge and biopsies can also be taken at the tip of the endoscope, and a laser can be used via the instrument to perform some types of surgery.

For evaluating sinuses, the endoscope is inserted through a small hole in the front of the head. To assess other organs, it can be inserted via the penis or female urethra into the bladder, via the vagina into the womb, and it may be used rectally to assess the colon.

Small endoscopes can also be used in anaesthetised horses to assess the inner surface of the joints (arthroscopy) and, via a hole in the abdominal wall, to examine the surface of abdominal

organs (laparoscopy).

Endoscopy can be undertaken at the owner’s premises, vet’s surgery or referral centre depending on the type of investigation needed. Results are usually available immediately unless samples are taken.

The cost ranges from around £50 for a very basic examination to around £550 for more thorough evaluation on a treadmill. Sedation of the horse requires extra cost, approximately £20-£50 – though some procedures may cost considerably more.

Ultrasound scanning

This can be helpful in the investigation of tendon, ligament and muscle lesions, as well as evaluating the chest lining, abdominal organs and eyes. Rectal use of an ultrasound probe allows imaging of the pelvic structures and is particularly useful for tracking changes in the ovaries, which aids pregnancy diagnosis. Ultrasound images can also be used when a biopsy is being taken, to guide the progress of a needle into an internal structure.

The area is spread with a special gel (first having been shaved), then a handset is moved over the skin. High-frequency sound is directed from the handset through the body to allow an image to be formed on a screen that represents the reflection and absorption of sound by the different types of surface tissue (the sound rapidly weakens so no information comes back from deeper tissues).

It can be undertaken at the owner’s premises or those of the vet or referral centre. Results are usually available immediately, unless the vet wishes to confer with a colleague. The cost ranges from around £30 for some basic reproductive work to £100-£200 for more time-consuming examinations with higher-resolution machines.

Electrocardiography

Electrocardiography (producing an electrocardiogram, or ECG), measures the electrical activity of the heart. It can be used to assess a variety of heart problems.

Electrodes are applied to the horse’s skin with small clips or adhesive patches, and are then connected to an ECG machine, a radio transmitter, or a small machine that records data that can be analysed by computer. The latter two methods are useful if intermittent problems are suspected, or the condition is only seen at exercise, as they allow long periods of heart activity to be recorded.

This can be done at the owner’s premises or those of the vet or referral centre. Results are usually available within a few days, as records have to be analysed. Costs from around £30-£100.

Radiography

Radiographs (X-rays) are particularly useful when examining broken bones and arthritic conditions, but can also be helpful when investigating lung and abdominal diseases, particularly in small horses and foals. However, the power of X-rays is insufficient to achieve good images of these areas in large horses.

Radiography machines work by emitting a focused beam of X-rays that passes through soft tissues, leaving a shadow on photographic film where the X-rays are stopped by harder tissues, including bone, and non-organic material such as metal.

The resulting negative image is blackest where the tissues are softest (more X-rays are allowed through), and whitest where a dense structure casts a shadow on the film. Changing the power of the X-rays results in images that show up the detail of the soft or hard structures to different degrees.

Alternatively, where computer plates, rather than photographic film, are used, images can be enhanced by the computer to allow visualisation of the detail of different structures. Computer analysis can also allow three-dimensional images to be built up from serial radiographs (a procedure known as computed tomography, or CT). The horse may require sedation for these tests.

Many veterinary practices have portable X-ray machines that can be used for examining some conditions at the owner’s premises, particularly if concerns exist about whether or not the horse can be moved. Better images can be achieved using higher-energy static machines located at practices and referral centres. Results are available immediately unless the vet wishes to confer with a colleague.

X-rays costs around £100-£400, depending on number of radiographs taken and the time involved.

Nerve blocks and joint blocks

These are most commonly used to identify a painful area when this is unclear during clinical examination. Once such an area has been identified, techniques such as radiography or ultrasound can be used to find the actual lesion that is causing the pain.

A local anaesthetic is injected around the nerves or into the joints in areas thought to be painful. If a particular nerve block removes the horse’s symptoms of pain (for example, it stops being lame), the source of the pain can be identified.

This can be undertaken at the owner’s premises or those of the vet or referral centre. Results are usually available immediately. It costs approximately £50-£150, depending on the number of blocks used.

Thermography

Changes in surface temperature are measured and formed into an image of the skin’s surface. This can allow identification of areas of increased blood flow, which may indicate inflammation due to injury. However, as it only shows changes in surface blood flow (rather than deep blood flow, as in the case of nuclear scintigraphy), this procedure is thought to be of less value than the other techniques mentioned here, and is less widely used.

The skin does not need to be specially prepared for thermal imaging, and as the technique is completely non-invasive, there is no recovery period. Thermography costs around £100 and can be carried out at the owner’s premises or at a hospital or referral centre. Results are usually available immediately.

Scintigraphy (gamma imaging)

Scintigraphy can be used to look at a number of conditions, but most often used to investigate pain and lameness to identify areas of the body where there is inflammation, or to monitor healing.

The horse is injected with a radioactive material that is taken up in greatest quantities by the cells that are dividing the fastest, or have the highest blood flow (inflamed areas). A gamma camera detects the radioactive particles, identifying the areas in the body where they are accumulating.

This has to be undertaken at a referral centre, where the horse must remain for 24 hours afterwards so that its waste (which contains radioactive particles for a short period) can be disposed of properly. Results available when the horse is collected. Scintigraphy costs around £600, includes sedation.

Magnetic resonance imaging (MRI)

MRI (or nuclear magnetic resonance, NMR) is particularly useful for elucidation of foot problems, which can be otherwise hard to diagnose, and can also be used to produce images of other areas of the limbs and the head.

This procedure involves detecting the differing magnetic properties of tissue, which generally relate to the concentration of liquid within them. MRI gives particularly good images of soft tissue structures, but because the area to be scanned has to be placed within a magnetic field (usually a cylindrical magnet), there are limitations as to which parts of the horse can be examined in this way.

This procedure takes place at a referral hospital. Results are usually available when the horse is collected, unless the vet wishes to confer with a colleague. It costs around £1,500 for high-resolution scans done under general anaesthesia; less for lower-resolution imaging done with the horse standing and sedated.

This guide to veterinary investigation techniques was first published in HORSE magazine (January ’05)