Abstract
In a previous study, the author found that serum testosterone (T) levels in male beagle dogs showed a circadian rhythm which was lowest at 12: 00, and increased to a peak at 18: 00-6: 00, thereafter decreasing until 12: 00. The reason was thought to be that dogs were breeding under rigid controlled conditons. The present study was performed to investigate the effects of lighting on the circadian rhythm of T level by means of a reversal of the lighting time zone, because lighting is considered an important factor in modulating T levels. Six male beagle dogs of 2 years were used in this study. The routine lighting time (8: 00-20: 00) and dark time (20: 00-8: 00) zone in the breeding room was reversed completely and T levels were measured at intervals of 1-5 weeks for up to 54 weeks. Blood samples were collected at 6: 00, 12: 00, 18: 00 and 24: 00. The results showed that the circadian rhythm of the T level and the T level at each blood sampling time did not change significantly within 54 weeks. As a result, it was recognized that the circadian rhythm of the T level in male dogs may not be affected by changes in the lighting time zone.
