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Stages in the life of corpora lutea may be divided logically into formation, function and regression. Mechanisms controlling each stage may be independent or overlapping depending on the species. Anderson et al.,(4) have pointed to lack of current evidence to allow a clear distinction between luteinizing hormone (LH) and luteotropic hormone (LTH) in farm animals. Initial LTH release is probably sufficient to form and maintain the corpora lutea for the normal estrous cycle (Aldred et al., 1). Maintenance of corpora lutea for the normal duration of an estrous cycle in hypophysectomized ewes (Denamur and Mauleon, 6) and sows (du Mesnil du Buisson and Leglise, 19) supports this theory. Nalbandov (20) has suggested a second release of luteotropin is initiated due to mechanics of placentation.