Reproductive seasonality and maturation throughout the complete life-cycle in the mouflon ram (Ovis musimon)

To document the process of physical and reproductive maturation in a long-lived mammal, the long-term changes in endocrine (follicle stimulating hormone-FSH, prolactin and testosterone) and morphological parameters (body weight, testis diameter, neck girth, sex skin colour, horn growth, wool growth, moult and pelage characteristics) were measured throughout the full life-span in a group of captive mouflon rams, Ovis musimon (n=4, 12-year study). Live body weight increased to a maximum at 7 years of age and declined in old age, while horn size (length and volume) increased throughout the full life-span. Every year there was a marked and consistent cycle in the blood plasma concentrations of FSH and testosterone, and growth of the testes, with peak reproductive function in September and October associated with the rut. The annual maximum in plasma FSH and testosterone concentrations, and the size of the testes increased progressively from 1-6 years of age (or later into the life-cycle for testosterone). There was also a marked annual cycle in plasma prolactin concentrations (peak in May and June), and growth of the horns and pelage. The annual maximum in prolactin concentrations increased throughout the life-cycle, while the rate of horn growth (annual increments) decreased. The overall conclusion is that neuroendocrine mechanisms regulate both the annual and the age-related changes in the reproductive axis, and reproductive maturation proceeds gradually through the life-cycle. Because the acquisition of adult characteristics (large body size, large horns, conspicuous male secondary sexual characteristics) greatly affects male competitiveness, sexual maturity is closely linked to physical maturity, and this occurs long after the initial onset of fertility at puberty.