Abstract
The present study investigates the influence of seasonal variations on testicular histomorphometric parameters of 15 adult
male Japanese quails (Coturnix japonica) and testosterone concentrations over a year. The gross anatomical and
histomorphometric study of both left and right testes was conducted. Serum testosterone concentration was measured by RIA
technique. Statistical analysis revealed that the testicular weight and morphological parameters of testes including volume, length, width, thickness, and circumference were significantly (P<0.01) higher during peak breeding season (June–July). In
contrast, all morphologic and histomorphometric parameters were significantly (P<0.01) lower during low breeding (Sept.- Oct.) and non-breeding season (Jan.- Feb). A significantly (P<0.01) higher serum testosterone concentration was recorded
during peak breeding season which showed a gradual decline during regressive breeding season and finally reached to
minimum during non-breeding season. Serum testosterone concentration showed a strongly significant positive correlation
(r=0.855) with all studied testicular parameters, however a strongly negative correlation (r=-0.819) was ascertained between
the relative humidity and serum testosterone concentration throughout the study period. It is concluded that Japanese quails
demonstrate an annular reproductive cycle. The testosterone secretion clearly elevates and stimulates gonadal function to its
peak in Japanese quails during summer season which gradually declines to bottom during harsh season of winter. It is
conceivable that the pineal gland (melatonin hormone) responds to environmental influences, particularly changes in length
of the daily photoperiod, and in turn exerts regulatory effects on the activity of the testis
