Kathleen D. Ryan

Determinants of Puberty in a Seasonal Breeder

Publisher Summary This chapter focuses on the determinants of puberty in a seasonal breeder. The evolution of seasonal breeding, natures contraceptive influences the time when fertility is first attained in the young female. Puberty occurs only during the breeding season. Thus, not only must the developing seasonal breeder be able to determine when she is sufficiently mature to begin reproductive cycles, she must also be able to determine when during the year onset of fertility will produce young during the spring and summer. The production of high-frequency luteinizing hormone (LH) pulses is clearly the pivotal force driving the transition into adulthood in the lamb. Therefore, further understanding of the timing of sexual maturation in this seasonal breeder depends upon ones ability to unravel how developmental and environmental signals modify the activity of the system generating pulsatile LH secretion by the pituitary. Based upon the work conducted in the adult and the patterns of LH observed in the lamb, there is little reason to suspect that the pubertal increase in LH pulse frequency in the young female sheep reflects anything other than an increase in frequency of the gonadotropin-releasing hormone (GnRH) pulse generator. The pubertal increase in LH pulses is occasioned by a lessening of negative feedback control of the GnRH pulse generator. The common neuroendocrine feature underlying the onset of puberty and the onset of the breeding season is the increase in GnRH pulse generator activity.