Early Estrus in the Cat Following Increased Illumination

THE BREEDING CYCLE of the cat is characterized by a definite anestrous period. The data of Foster and Hisaw (1) indicate that in the region of Madison, Wisconsin, cats are usually anestrous from September to January although a few may be found in this phase of the cycle at still later dates. Extensive observations by Windle (2) on several hundred cats over a period of 11 years show that estrus rarely occurs (under laboratory conditions in Chicago, Illinois) during the season beginning with July and ending with January. Accordingly, Windle regards the period from February to June, inclusive, as the normal estrous season. Experience over the past 3 years in Cambridge, Massachusetts also confirms these observations on the duration of the anestrous period. Few animals exhibited spontaneous estrus in the early part of January (table 1). Many investigators have induced estrus during the anestrous period by the injection of appropriate hormones.