Seasonal cyclic pituitary and testicular activities in rams

Adult rams were subjected to various photoregimes for more than 4 years to determine whether pituitary and testicular activities are inherently cyclic . Adult rams (three treatment groups, each with 12 rams) of the Arcott bree ds were housed in environmental rooms kept at 15 degrees C and exposed to s hort days (8 h of light and 16 h of darkness) for 1 year to dissipate the p ossible influence of normal environmental changes, The rams were then expos ed to long days (16 h of light and 8 h of darkness) for 3 months to induce testicular regression. Subsequently, rams in Treatment Group 1 were exposed to short days for 39 months. Rams in the other treatment groups were expos ed either to alternating 4-month periods of short days and long days for 16 months followed by 21 months of short days (Treatment Group 2), or to alte rnating 4 month periods of short days and 2 month periods of long days for 12 months followed by 4 months of short days, and then a reversal in daylen gth to 21 months of long days (Treatment Group 3). Exposure to the fixed da ylength photoregime was followed with a change in daylength to test the ret ention of photosensitivity in the rams. Scrotal circumference and serum con centrations of follicle stimulating hormone (FSH), testosterone and prolact in were measured every 2 weeks throughout the study. In the rams exposed to short days only (Treatment Group 1), no cyclic change in hormone levels or scrotal size was apparent; FSH levels, testosterone levels and scrotal siz e all rose significantly early in the 39 months period and remained above b asal levels. In the rams of Treatment Groups 2 and 3, the changes in the ph otoperiod cycles induced rhythmic pituitary and testicular activities which persisted for the first year of constant daylength, faded or disappeared t hereafter. Prolactin levels in each treatment depended on the light regime, with levels being depressed or elevated during short or long days, respect ively (P < 0.01). All rams responded to the final change in photoperiod wit h an appropriate increase or decrease in the pituitary and testicular activ ities. These observations indicate that persistent memory of previous photo period change accounts for the 'apparently spontaneous' rhythms in pituitar y and testicular activities in the short term, but the decline of the regul ar changes as the memory fades does not support the existence of inherent c yclicity in reproductive functions in rams of the Arcott breeds. Crown Copy right (C) 1999 Published by Elsevier Science B.V. All rights reserved.