Serum testosterone in Arabian stallions during breeding and non-breeding seasons in Iran

The study was conducted to investigate the serum testosterone concentrations of Arabian stallions during breeding and non-breeding seasons under natural photoperiodic condition in west south of Iran (Khuzestan Province; latitude 48:40 degree N, longitude 31:20 degree E and altitude 22.5 m). The blood samples (10 ml) were collected from the jugular vein, and it stood at room temperature for 3 h and was centrifuged. The sera were kept at -20 degree C until assayed by radioimmunoassay. The results show that total serum testosterone levels (ng/ml) in Arabian stallions was higher in May to June (Summer Solstice 1.08 plus or minus 0.078) than in November to December (Winter Solstice; 0.65 plus or minus 0.11) (p < 0.05). We conclude that serum testosterone concentration during the non-breeding season is lower than that of the breeding season. The results confirm a seasonal rhythm in the reproductive cycle of Arabian stallions over the year in this specific region.