Pattern of LH and testosterone secretion of adult male fallow deer (Dama dama) during the transition into the breeding season

Pituitary secretion of LH and testicular secretion of testosterone were investigated during the transitional period from the non-breeding to breeding season of mature male fallow deer exhibiting either normal transitional patterns or shortened transitional patterns in response to summer melatonin treatment. Melatonin implants were administered to 4 bucks for a 150-day period starting 130 days after the winter solstice. Four contemporary bucks served as controls. Melatonin treatment advanced rutting activity, testis development and neck muscle hypertrophy by 6-8 weeks. Profiles of plasma LH and testosterone, based on a 30-min sampling frequency over 24 h, were obtained from 3 treated and 3 control bucks on 4 occasions over the period spanning the transition into the breeding season. In control bucks, LH and testosterone pulse frequency were low (0-2 pulses/24 h) in January and increased (5-7 pulses/24 h) in February. By March and April (pre-rut and rut periods respectively) there was a two-fold increase in basal plasma LH concentrations, a decline in LH pulse frequency (0-1 pulse/24 h) and episodic surges in plasma testosterone concentrations. Melatonin treatment resulted in a shift in hormone profiles, with highly pulsatile patterns of LH and testosterone secretion (7 pulses/24 h) occurring earlier in January. The subsequent post-rut profiles of treated bucks were characterized by lower basal plasma LH concentrations, and reduced frequency and amplitude of plasma testosterone surges.