Includes bibliographical references (leaves 166-195) / xxi, 195 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Addresses the nature of the central mechanisms involved in the regulation of the circadian pattern of secretion of the pineal hormone melatonin in the highly seasonal Suffolk breed of sheep. Provides new information on the behaviour of the onset and offset of melatonin secretion under different photoperiodic conditions. / Thesis (Ph.D.)--University of Adelaide, Dept. of Animal Sciences, 1991?