The basic, routine blood tests are haematology and biochemistry. Veterinary surgeons can also measure, with a high degree of accuracy, the level of certain minerals, namely copper, zinc and selenium, and of vitamins B, D and E. Determining the level of calcium, phosphorus, magnesium or vitamin A is not possible, however, because if they are needed they are released into the blood from the horse’s reserves, more precisely from the liver and the bones. For that reason a blood test can look normal even if the horse is short of the nutrients mentioned above. It is worth remembering that values outside the reference range are often caused by a diet that is too rich or too poor, or even by stress.
How often should blood tests be done? If you own a healthy horse, haematology and blood biochemistry, together with the additional minerals and vitamins, are best carried out regularly once a year. If, however, your horse has health problems, is older, or is exposed to intense work, it is worth running such a test more often, and always when needed, for example after introducing a medicine or a supplement, to check whether the changes you have made are effective. In that situation you can retest only the values that interest you.
For reliable results, the right amount of blood must be taken into a sterile tube by a veterinary surgeon. This is best done in the morning, and the horse should be fasted and relaxed, because stress and exercise have a significant effect on blood values. For results to be compared, it is important that this is done at a similar time and under similar conditions. As for the time of year, the test is worth doing before the change to the summer or winter coat, so that if there are shortages the horse’s body can be prepared for the extra demand.
What exactly are haematology and blood biochemistry? Haematology measures red cells, white cells and platelets. For example, low red-cell values can indicate anaemia, and values that are too high can indicate dehydration. Biochemistry, meanwhile, shows the levels of various proteins, enzymes, electrolytes and other biochemical substances. For example, urea values that are too high can indicate a diet that is too high in protein. Enzymes worth watching in the biochemistry are the liver enzymes, that is AST, ALP and GGT. Raised values most often indicate liver damage, but they can also point to poisoning, a worm burden or an unsuitable diet.
Interpreting blood results is not simple and requires extensive specialist knowledge, so it should not be done on your own. In the same way, correcting vitamin and mineral shortages should be discussed with a specialist in horse nutrition, because giving supplements at random can cause even greater shortages and imbalances. For example, the calcium-to-phosphorus ratio (Ca:P) in the diet of adult horses should lie between 1:1 and 3:1, because excess phosphorus adversely affects the absorption not only of calcium, but also of copper, iron, magnesium and zinc. It is also worth checking whether the ready-made concentrate you feed is suited to the age, physiological state and physical activity of your four-legged charge, and whether it covers the requirement for vitamins and minerals.