Under
the Microscope



Supplied by Equine Veterinarians Australia (EVA)

Author: by Dr Sue Beetson

Laboratory testing can be a valuable source of information in relation to equine health

Laboratory scene


Over the last 20 years, laboratory testing has become a useful and, in many cases, an essential tool in the diagnosis and management of numerous medical conditions in horses from all walks of equine life. Throughout Australia, there are a numbers of veterinary pathology laboratories that specialise in providing an extensive pathology service for equines and other domestic animals - offering what is both a timely and effective way of finding out what is happening inside the body and giving direction as far as treatment is concerned.
The procedures that are available via equine pathology services include, to name a few, blood tests for disease, hormone and pregnancy testing, examination of lung samples, basic nutrition testing and biopsies of skin and 'lumps and bumps'. The results of these tests are then used by the veterinarian who requested them, in consultation with the horse owner, to make important and accurate decisions concerning treatment and management.

BLOOD TESTING

Probably the most commonly requested form of examination are routine blood tests, which are usually recommended by a vet when the fitness or performance of a horse is in question, or to look for evidence of illness. After extracting a sample of blood (usually from the jugular vein), the vet places it into specific tubes and submits it to the laboratory, where it undergoes a two part testing procedure - the first part being haematology. This looks at the numbers of red and white cells in the blood to help determine if the horse is anaemic, dehydrated or has an infection or virus.

A blood sample being taken from the jugular vein of a horse

Biochemistry, the second part of routine blood testing, measures specific substances in the blood that, in a healthy horse, exist at low levels. With disease or illness, however, there is an increase in individual substances, depending upon which body part (liver, kidney, muscle and so on) is affected, therefore allowing the vet to make what is known as a differential diagnosis (decision between a number of possible conditions). Electrolyte (sodium, potassium and chloride) levels can also be measured, which helps determine if a horse is getting enough salts or has any abnormal loss of fluid, as might be the case with diarrhoea. Measurement of protein levels in the blood is also possible, with the results assisting to determine if a horse is dehydrated or, in a foal, if enough colostrum has been received from its dam's milk.

LUNG AND THROAT WASHES
In cases where poor exercise tolerance and/or coughing is a problem with a performance horse, a vet will often consider doing a 'wash' of the lungs or throat to help identify the cause. After fluid has been taken from the lungs (bronchial wash) or throat (tracheal wash), it is examined by a veterinary pathologist, who looks at the cells in it to determine the type of reaction that is causing the problem. Some of the underlying reasons for both coughing and a drop in performance can be a bacterial infection, allergy or chronic lung bleeding so, once it has been worked out which one is responsible on the basis of the 'wash' results, the most appropriate treatment, along with changes to the horse's environment and work regime, can be implemented.
In cases of pneumonia, where the horse has a severe infection of the lungs, the laboratory will often culture the fluid from a bronchial wash to determine what type of bacteria is causing the infection and will also test the bacteria against various antibiotics - allowing the treating vet to select the most suitable one for treating the case.

BACTERIAL AND PARASITIC INFECTIONS
Samples from wounds, skin, urine and eye discharge are also often taken by veterinarians and sent to a laboratory for analysis. If a bacterial infection is suspected, various techniques will be used to grow bacteria from the submitted sample and, as with a lung wash, this will then be tested against various antibiotics to help decide analysis. If a bacterial infection is suspected, various techniques will be used to grow bacteria from the submitted sample and, as with a lung wash, this will then be tested against various antibiotics to help decide upon the best treatment strategy. In the case of a manure sample, a check of parasite (worm) levels can be done at a pathology laboratory by counting the number of worm eggs present and observing which types are most evident, a procedure commonly known as a faecal egg count. This information enables vets and horse owners to find out if their worming program is working effectively or if there are specific areas that need more attention.

Equine worm eggs seen in a faecal worm count

Even the best-cared-for horses sometimes develop mysterious skin conditions or, especially in the case of an older equine, a lump will be found growing. Often, the only way of knowing the cause of these is to remove a piece and send it off to a laboratory, where a very small sample of the tissue can be examined under a microscope. The treating vet can then be advised by the pathologist as to whether the condition is an infection, an allergic reaction or a tumour, allowing decisions to be made about whether the lump should be removed and how it would be best treated. Results such as those gleaned from this type of test also inform the owner as to what the future may hold for their horse over the next few years.

PREGNANCY AND GENETIC TESTING
Samples of blood can yield many types of information, including whether a mare is in foal. Two tests are available ; one that will detect pregnancy between day 42 and day 120 and the other test detecting pregnancy from 80 days to foaling. These tests are particularly useful for miniature horses and ponies, where routine methods of pregnancy diagnosis are difficult.
A blood test that can be done on newborn foals to ensure they have received enough colostrum from their mother is another useful procedure for maximising the success of a breeding program, as are the new DNA tests that are now available to check for inherited conditions, such as Immunodeficiency in Arabs. There is even a test to predict a foal's coat colour before it is born!
The complete list of tests available through a veterinary pathology laboratory is very large and therefore isn't able to be covered in a single article, so this is just a 'taste' of the services on offer. It's important to be aware, however, that most testing of this nature is also not able to be done directly on behalf of a horse owner (as samples must generally be submitted through a registered vet), so veterinary assistance is required not only to take the sample, but also to make observations that may help in the diagnostic process and to implement the results of the testing in a way that best facilitates recovery.
Horse owners can rest assured that the laboratory testing service available in Australia for their animals is just as good - if not better - than that available to the general human population.

Supplied by Equine Veterinarians Australia (EVA).
For more information go to the web site: www.eva.org.au

Dr Sue Beetson
A Murdoch University Veterinary School graduate with a research honours degree and a PhD in Clinical Biochemistry Sue Beetson is a Clinical Pathologist for VETPATH Laboratory Services in Perth and has a special interest in Equine Pathology.