Researchers Evaluate Equine Hematology Parameters

Italian researchers believe that a wide number of “healthy” variables—such as breed and geographic location—might impact horses' blood test results. And with the current textbook reference hematology values being based on the Thoroughbred horse in the United Kingdom, the team believes it might be time to develop new reference values for different breeds in different parts of the world.

“The risk is not having a correct diagnosis and having it really wrong, because it is really impossible that horses living in different environments would have the same blood parameters,” said Barbara Padalino, PhD, researcher at the University of Bari Aldo Moro Veterinary School, in Bari.

Although some research has focused on different hematology parameters for different breeds, no studies have evaluated the different values for different regions, she said. Some previous study results suggest climate could impact hematology parameters, but current reference values do not take climate or geographical location into account.

Hematology values are very important in assessing general health, fitness, stress, and welfare in performance—especially racehorses, Padalino said. They can also be indicators of overtraining, allowing stable managers to make informed decisions about changes in training programs for individual horses.

Inaccurate reference tables for these parameters could lead to faulty information about health, fitness, stress, welfare, and overtraining, Padalino said. New reference standards should ideally be developed for every breed as well as geographic region, she added. Other factors likely to influence healthy parameters—and should therefore also be taken into consideration—include age and sex.

Padalino and colleagues investigated the hematologic parameters—red blood cell count, hemoglobin (a protein that carries oxygen in the blood), mean corpuscular hemoglobin concentration, and mean corpuscular volume (which is used in determining the average size of the red blood cells) —in 100 seemingly healthy Standardbred trot-racing horses in southern Italy. They then compared these results to the standard reference hematologic parameters and found some major differences.

Specifically, they found that their Southern Italian trotters had more red blood cells (termed erythrocytes), but that they were smaller in size and had lower hemoglobin concentrations, Padalino said. In general, the trotters also had mean corpuscular volume values that were both lower than references from U.K. laboratories and “always in the lowest part of the range proposed by previous studies,” she said.

Part of these differences could simply be due to natural adaptation to habitat, suggested Padalino. “During summer in these regions, the temperatures are very high and horses must race and train, often under difficult environmental conditions that could lead to dehydration or other physiological adaptation that enable horses to cope with the challenging conditions.”

She also discovered that 11% of the study horses had been infected with an organism that causes equine piroplasmosis, but none of the horses showed any clinical or hematologic signs. This suggested the possible development of a “genetic breed resistance” to the disease among horses in this region, she said.

Padalino cautioned that some of the differences in hematologic parameters could be due to poor training programs and management: “(Based on these parameters, we suggest) that the traditional training practiced in southern Italy is too hard with too few resting days and too many races,” she said.

“Hematology is influenced by genetics, feeding, and the traditional method of rearing (pasture, single box) and training (more or less intensive),” said Padalino, “so it is very important to have reference values for a population to do a better diagnosis in particular in case of poor performance in racehorses.”

The study, "Observations on the Hematology of Standardbred Horses in Training and Racing in Southern Italy," by Padalino; Giuseppe Rubino, DVM, PhD; Rosanna Lacinio, DBio; and Ferruccio Petazzi, DVM, will appear in an upcoming issue of the Journal of Equine Veterinary Science

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.

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