Abstract
It has long been recognized that the seasonal pattern of reproduction in many species is controlled by environmental photoperiod (Yeates, 1949; Hafez, 1952; Menaker, 1971; Follett, 1978; Turek & Campbell, 1979). Insight into the mechanisms whereby photoperiodic cues are transduced into endocrine messages which govern gonadal function, however, has been gained more recently. It has been proposed that in ewes this process of transduction includes a marked change in the hypothalamo–hypophysial system which controls the tonic mode of gonadotrophin secretion (Legan, Karsch & Foster, 1977). Based on this change, a scheme was presented for the endocrine control of seasonal breeding in the ewe. This report will describe this scheme and then present a series of experiments we performed to test it.
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