Plasma leptin concentrations during the reproductive cycle in the native Thai chicken (Gallus domesticus)

Plasma leptin concentrations were investigated during the reproductive cycle in the native Thai chicken. The plasma leptin concentration was high during non-laying (0.69 ± 0.15 ng/ml), lowered to a minimum concentration during egg laying (0.07 ± 0.02 ng/ml), and gradually increased during egg incubation and rearing of the chicks (0.53 ± 0.22 and 0.74 ± 0.29 ng/ml, respectively). However, the differences were not significant. Incubating chickens that were deprived of their nests for 3 weeks showed a significant decrease in plasma leptin concentrations (0.29 ± 0.04 ng/ml, P < 0.05) compared to those of their corresponding incubating controls (0.77 ± 0.08 ng/ml). Similarly, plasma leptin concentration of chickens that were deprived of their chicks for 4 weeks was significantly lower (0.09 ± 0.11 ng/ml, P < 0.05), when compared to those of chickens that rearing their chicks (0.71 ± 0.18 ng/ml). These findings taken together with the results that the low plasma leptin concentrations were observed in chickens having relatively greater ovary and oviduct weights led to the suggestion that circulating leptin concentrations are associated with the reproductive states of the birds, especially the ovarian activity (i.e. ovarian steroid hormone concentrations) in the native Thai chicken, a tropical and continuous breeding species.