Serum leptin concentrations in Lipizzan fillies

To determine seasonal changes in circulating leptin concentrations, as well as leptin fluctuations in various patterns of seasonal ovarian activity, blood samples were taken in 107 Lipizzan fillies aged 1-4 years over the whole year from January to December. Serum concentrations were measured in samples obtained once a month (leptin) or twice a month (progesterone), and evaluated with respect to the age of animals (yearlings, 2-, 3- and 4-year olds) and the pattern of ovarian activity (anoestrous, seasonal cycle, prolonged cyclicity, continuous cyclicity). The mean and monthly leptin concentrations in 3- and 4-year olds were significantly higher than in yearlings and 2-year olds (p < 0.001). Circulating leptin levels in 3- and 4-year olds increased significantly in summer, to peak in August and then decline significantly (p < 0.001) in autumn. The fluctuations in younger fillies were less evident. The highest mean serum leptin concentrations were observed in fillies exhibiting continuous cyclicity and the lowest in those, exhibiting seasonal cyclicity (p < 0.001). In anoestrous fillies, leptin concentrations were lower than in fillies with prolonged or continuous cyclicity but higher than in fillies with seasonal cyclic activity (p > 0.05).