“…When suckling is maintained for an extended period, resulting in prolonged lactation, this post-partum dioestrus is followed by cycles with a prolonged dioestrous phase (Parkes, 1926;Crew & Mirskaia, 1930;Selye & McKeown, 1934c;Bruce, 1961;Nagasawa & Yanai, 1976; Tomogane, Ota, Unno & Yokoyama, 1976). Removal of young during the 3-week post-partum dioestrus leads to a rapid resumption of regular oestrous cycles (Crew & Mirskaia, 1930;Ota & Yokoyama, 1965;Moltz, Levin & Leon, 1969;Zarrow, Johnson, Denenberg & Bryant, 1973;Maneckjee & Moudgal, 1975).…”