The changes associated with puberty were studied in thirty-one red deer stags between 3 months and 3 years old. The majority of deer were born in June.
During the first 11 months of life, there was a gradual proliferation of spermatogonia in the seminiferous tubules. From May to October, between 11 and 16 months of age, a marked increase in the size and weight of the testes followed, the content of testosterone also began to rise and spermatogenesis was initiated. Over the same period, the weight of the epididymides, seminal vesicles, ampullae and prostate, and the concentration of seminal fructose increased. The antler pedicles began to develop in May, and antler tissue was evident by August.
The testes and accessory glands reached a peak in activity in October at 16 months of age but the development of the secondary sexual characteristics, including growth of the neck mane and 'stag' winter coat and the cleaning of the antlers, was not completed until 2 to 3 months later. Unlike the adult stags in October, the yearlings showed no rutting behaviour.
Following this peak in development, the testosterone content of the testes quickly declined to a low level, though spermatogenesis continued at a reduced rate through the winter and spring. Over this period, the weights of the accessory glands declined. In June, at 2 years old, spermatogenesis was arrested, the accessory glands were involuted, and the first set of antlers was cast. This marked the end of the first reproductive cycle; the testes and accessory glands redeveloped in October. In this second cycle, the secondary sexual characteristics developed earlier and some aspects of rutting behaviour occurred.
Puberty in the stag was defined as the period from 9 to 15 months of age, from the onset of androgen secretion to the completion of spermatogenesis. These changes were considered similar to the changes which occur each year in the adult in preparation for the breeding season.
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