The aim of this study was to evaluate the effect of intensity exercise on blood levels of red blood cells (RBC), hemoglobin (Hb), lactic acid (LA), glucose (Glc), triacylglycerides (TG), total plasma proteins and urea according to sex of horses. Three-year-old Arabian stallions (n=20) and mares (n=18) were observed during their race - training. Blood samples were taken at rest, immediately after exercise and 30 minutes after the last sampling. The higher increase of plasma Glc and proteins was noted just after exercise in mares, compared to stallions. The differences in the values of LA, Hb, Glc and TG were observed also 30 minutes after the end of training in two investigated groups of horses. The exercise of the same intensity effects of the mare's metabolism in a higher degree, than of the stallion's one.

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