Leptin Fluctuations in Trained Horses, During a Work Season

• The effect of long-term training on plasma leptin level in horses was studied.
• The training routine led to a decrease in the plasma leptin level in young horses.
• In adult horses, training did not influenced the plasma leptin concentration.
• The plasma leptin and cortisol levels were not dependent on each other.

The effect of long-term training on plasma leptin concentration in horses remains unknown. The aim of the study was to evaluate the influence of training on plasma leptin concentration in race and sport horses, during a work season. Thirty-four clinically healthy horses were assessed during their race and equestrian training. They were 12 adult sport, saddle-breed stallions (group S), 12 naïve, 3-year-old Purebred Arabian horses involved in race training (group R1), and 10 4-year-old Purebred Arabian horses, which were continuing their race career (group R2). Blood samples were collected at rest, four times during the training season, and from March to September. Plasma leptin and cortisol concentrations were measured and analyzed. In group R1, the mean value of leptin gradually decreased from March to September (from 10.8 ± 7.4 ng/mL to 1.1 ± 0.4 ng/mL), whereas the plasma cortisol concentration was low and unchangeable during the study (63.2 ± 16.1 ng/mL). In group R2, plasma leptin concentration was generally below 1.0 ng/mL despite the fact that the cortisol concentration increased during the study, reaching the mean value of 656 ± 693 ng/mL in September. In group S, the studied parameters did not exceed the values of 1.90 ± 0.22 ng/mL for leptin and 75.0 ± 21.2 ng/mL for cortisol. The values of coefficient correlation for studied parameters were statistically insignificant. Thus, the plasma leptin concentration is not dependent on cortisol concentration in trained horses. The training routine leads to decrease in the plasma leptin concentration in young horses.