FACTORS AFFECTING TESTICULAR FUNCTION

1. When does testicular function become manifest?

2. How does puberty begin in the male?

3. What is the purpose of photoperiod influence on testicular function?

4. How does increasing photoperiod affect sheep and goats? Is this different in the stallion? Are cattle and swine influenced by photoperiod?

5.

Testicular function becomes manifest at the onset of puberty. It is believed that puberty is correlated with a decreased sensitivity of the hypothalamus to testosterone so that LH is secreted in greater amounts. An increased LH concentration stimulates the Leydig cells to secrete testosterone in greater quantities, and all aspects of testosterone function begin to appear. FSH is essential for the initiation of spermatogenesis at puberty.

In some species, photoperiod (length of daylight) changes have a marked influence on testicular function. Photoperiod is also related to ovarian activity in the female of these same species. The purpose of photoperiod influence is the coordination of birth with favorable weather conditions. Sheep and goats have major periods of testicular regression during increasing photoperiods, which is restored by decreasing photoperiods. In the stallion a decreasing photoperiod reduces testicular function. The pineal gland (also known as the pineal body) is an endocrine gland attached by a stalk to the dorsal wall of the third ventricle of the cerebrum. The pineal gland is inhibitory to the gonads and is the principal mechanism in the known affect of photoperiod on testicular and ovarian function. The pineal gland mediates the photoperiod response in the ram and ewe and is probably involved in the response of the other species. Testicular function and photoperiod in cattle and swine are related only to a minor degree. When spermatogenesis is stopped during photoperiod inhibition, FSH is again required for its initiation.

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