REBECCA WATSON, MSc RVN, in an article republished from Equine Health magazine, provides an insight into the various blood analyses that your vet may from time to time have performed for horses in your care.
Establishing the most reliable result
It is important to remember that a blood analysis is just a snap shot of that individual’s biochemistry at that particular moment in time. A large number of external factors can influence a horse’s blood values; they will fluctuate depending on the time of day, the time of the last feed, time and duration of exercise, hydration status, stress levels, diet, the age of the horse, breed, sex and also the horse’s level of fitness.
A wise vet once told me, “Always look at the horse, if it looks well, it probably is. Don’t use a blood test as an excuse not to look at the horse.” In other words, people can sometimes get too caught up in looking at the numbers on the page and lose sight of the bigger picture; blood results should be used as a complement to what can be seen and felt about the horse.
It is therefore critical that sampling procedures are standardised to ensure meaningful results are attained. Blood samples should be taken at the same time of day, ideally before feeding and before exercise when the horse is resting calmly in the stable. If a horse is excited or stressed at the time of sampling, it can cause a “fight or flight” splenic contraction which will falsely elevate red cell values.
The blood samples themselves must be handled carefully and shipped to the laboratory in as short a time as possible to ensure accurate reporting of results. Samples should be taken in the appropriate sampling tubes (see table) according to the tests to be run. If samples become haemolysed (red blood cells damaged or broken down due to incorrect handling) then blood results may be inaccurate.
Textbook references are not always applicable, especially for biochemical tests, as analytical methodology varies widely between laboratories. Furthermore a range of “normal” values in a group of individuals may be seen in the same yard. The best normal values come from the horse itself from previous samples (from the same laboratory).
Reading the results of one biochemical value will not give a definitive diagnosis, many parameters are intrinsically related to each other and it is necessary to look at the whole blood analysis to be able draw conclusions. It is vital to be able to recognise patterns, figures and understand the dynamics between these different parameters.
Red cell values will increase to a certain level as fitness increases in the equine athlete. The overall aim of training is to increase the oxygen carrying red blood cell component of the blood so that the equine athlete can perform faster and for longer.
Most nutrients have multiple roles in the body and hence any deficiencies will affect the function of a number of body systems. Deficiencies can manifest as abnormal behaviours, premature fatigue during competition and other performance problems or issues with grazing and consuming feed.
Some vitamin and mineral levels can be easily assessed by blood sampling; selenium, vitamins B, D and E. Others, such as vitamin A, copper, calcium, phosphorus and magnesium are a different story; because of homeostatic regulation in the body these substances may be released from stores (e.g. from the liver / bone) so that blood test results may appear normal, even if the horse has a deficiency.
Using feed additives without proper guidance can be detrimental to the horse’s health as certain vitamins and minerals can be dangerous if overdosed (e.g. selenium, iron, iodine, vitamins A, D and K). The best protection against dietary deficiencies is to have the dietary intake of the horse calculated, to ensure that the horse is consuming the correct amount of vitamins and minerals, and that the ratio of these minerals is correctly balanced for optimal health (and growth in young horses) particularly in the case of calcium:phosphorus and copper:zinc.
Inflammatory proteins can be measured in the horse to aid the diagnosis of inflammatory conditions. Traditionally Fibrinogen was measured and is a good indicator of tissue damage; it generally rises to a peak at 10 days after the initial disease process and slowly returns to normal as the disease is overcome.
Serum Amyloid A (SAA) is a more useful inflammatory marker in the horse as it is highly sensitive, rapidly rising in response to infection and inflammation, it can be used to monitor the horse’s response to treatment as it will fall more quickly than Fibrinogen.
Globulins can be examined more closely by protein electrophoresis, which will create a ‘panel’ of alpha, beta and gamma globulins. Different proteins have different responses and kinetics and can give a more definitive diagnosis (e.g. parasitism/ neoplasia) in horses with chronically elevated globulin levels.
Blood sampling has become routine in equine practice and is a highly useful tool to aid clinical diagnosis. When used appropriately blood results are helpful in not only diagnosing health problems, but also as a way of monitoring response to treatment and the progression of disease processes, whether that is positive or negative. The expense of carrying out blood sampling is often outweighed by the cost of missed or delayed diagnosis, in both financial and welfare terms.
© Equine Health, vol 2016, issue 30
Articles republished from Equine Health are kindly supplied by Chris Keate, editor, Equine Health. Christine Keate has been a journalist in the equine industry for 20 years. She was a Horse and Hound columnist on health and welfare issues and then editor of Horse Health for five years, before launching Equine Health as part of MA Healthcare. She has a deep love and understanding of horses and the issues that affect their health and well-being.
Equine Health magazine brings together equine vets, industry professionals and horse owners; improving communication and understanding, leading to better equine health and welfare.