Possible homologies between photorefractoriness in sheep and birds : the effect of thyroidectomy on the length of the ewe's breeding season

Abstract

Comparisons are drawn between the photoperiodically driven breeding cycles in long-day birds and short-day mammals, emphasizing the importance of photorefractoriness as a key regulator in the timing processes. It is argued that the two types of breeding cycle may not be so radically different as previously thought and, indeed the cycles may be strictly homologous. Evidence in support of this comes from the role of