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Blood Tests for Performance Horses: How Helpful Are They?By Kentucky Equine Research Staff · January 17, 2013

Owners and trainers of performance horses are always looking for ways to evaluate the condition, fitness, and overall health of the equines in their care. Are managers feeding the right hay and grain in the right amounts at the right times? Are they working the horses too much, or not enough? Does a particular horse have some hidden problem of which the owner is unaware?

Blood analysis seems like a way to answer these questions. After all, the result will reveal practically everything that’s going on with this specific horse, right? Maybe, maybe not. A blood test can be helpful in determining a horse’s status, and a series of blood tests can be even more helpful. Unfortunately, however, no analysis of blood chemistry can provide a definitive answer to every nutrition, training, and performance question.

Per Spangfors, a veterinarian with Euro-Vets AB in Simlangsdalen, Sweden, submitted a paper for a Kentucky Equine Research (KER) nutrition conference on the topic of blood analysis and its relationship to feeding performance horses. According to Spangfors, there is a great danger with blood analyses in that what the owner ends up with is a set of figures on a piece of paper.

He wrote, “Most people regard those figures as the absolute truth, and that this figure is static until you take the next blood sample. If the person in question also compares that figure with a reference value and finds his horse’s value within the expected limits for health, then the clinical picture is of no concern to him, and no matter how the horse looks, he is sound according to the blood test. If the horse starts in a competition and fails, the person raises his eyebrows and wonders why the blood test failed to tell him that the horse was in no condition to compete. This person should have realized that the figure in his hand is a photograph of a dynamic situation, and was only valid for that particular situation. He should also know that the clinical picture of his horse is the truth, no matter what the blood test and normal values say, and he should have consulted a specialist about the interpretation of the analyses, but the absolute truth is never revealed.”

The horse’s blood chemistry is constantly changing in response to the time of day, exercise regimen, diet, time of feeding, stress, and other parameters. Even if successive samples are taken at the same time every day, Spangfors wrote, interpretation of blood tests is an art.

“It takes knowledge, intuition, and fantasy to do a good job. You have to see patterns in the figures and understand the dynamics between the different parameters. To be an experienced interpreter, the feedback from the veterinarians, trainers and horse owners is essential. First, when you compare the real situation with the test results in discussion with the horse handler, you can develop your skill in reading test results. In order to use blood samples to evaluate nutritional status, it all depends on how you do it. If you have a reliable laboratory and know which parameters to analyze, and when to take the samples, it is possible to make a good guess on the nutritional status for some nutrients.”

He continued, “As a general rule, it is much easier to see when something is wrong, than to see when the situation is optimal. In other words, it is easy to see when you can expect poor performance, but almost impossible to see when the horse is in perfect shape. Or, it is easy to see a copper deficiency, but impossible to see when copper for this horse is optimal. We use blood tests to scan all the individuals in a stable, and we can get a rough picture of the health status, performance status and nutritional status by doing this. One must use the test results as a complement to what you see and what you feel about the horse when in training. We find a good clinical relevance in the test results, but we also find imbalances among the  parameters, and are often able to correct these imbalances before clinical symptoms occur.”

“Normal range is a statistical way to help understanding non-normal situations,” Spangfors said. “But as it is just a statistical value; many exceptions exist. Furthermore, we can have many different normal ranges, one for the whole population (widest range), one for clinical situations (most used range), and one for performance evaluations (narrowest range). Every laboratory must have its own set of normal values, as analysis procedures, analytical temperatures, hardware, and sample handling differ among laboratories. To simply use literature values is meaningless. The best normal values come from the horse itself. Previous blood tests from the same horse can be used if the samples are sent to the same laboratory and have been taken on similar occasions as the previous ones. It is hence a good practice to standardize your sampling procedures and make notes of sampling conditions for future use.”

Spangfors explained, “Most of the parameters analyzed from blood give an unspecific picture of the biochemical processes. Consequently, we have to analyze many unspecific parameters in order to get a more specific illustration of the situation. By doing this we see patterns in the figures, and do not necessarily have to have values outside the normal ranges to spot pathologic situations. This in turn makes each blood test more difficult to explain. Many nutritional imbalances affect the hormonal system. And as hormones always have more than one target organ, and there are many correlations between parameters, you can be certain to find more than one parameter diverging from normal. This is why you can see a pathologic  pattern if you analyze many parameters. Many metabolic active hormones are possible to analyze even in mailed blood samples, such as insulin, cortisol, T4 and T3, while others, growth hormone (GH), insulin-like growth factor-1 (IGF-1), glucagon, parathyroid hormone (PTH) and calcitonin, are for research or hospitalized horses only. To measure hormone levels requires special attention and is best used to confirm a suspected disturbance discovered by the ordinary blood test. It is of little use to analyze hormones without making a stimulation or inhibition test, because hormone levels show a natural variation during the day due to feeding, exercise or circadian rhythm. Thus, insulin, T4, T3, and cortisol can be stimulated by glucose tolerance tests and T4 and T3 alone by giving thyroid releasing hormone (TRH). Tolerance tests often give valuable information of an individual’s response status, and can give information on how this particular horse should be fed.”

“Blood analysis is also an excellent tool for determining nutritional status in an individual horse, but the exceptions are many,” Spangfors concluded. “Knowledge of the dynamic processes involved and a critical eye are necessary. Normal values should be used with great care, and comparing a new sample to previous samples from the same horse is the preferable method.”