Gestation periods in the Père David's deer (Elaphurus davidianus): evidence for embryonic diapause or delayed development.

It has been suggested that the gestation length of the Père David's deer is around 280 days, which is significantly longer than any other deer species except the roe deer (approximately 300 days) which exhibits embryonic diapause. The present study was designed to determine whether embryonic diapause exists in the Père David's deer by accurately monitoring gestation length. There was no difference in gestation length (283-284 days) between animals mated early and later in the breeding season. Hence, although Père David's deer exhibit a longer gestation period than that predicted from maternal body weight, there is no evidence for seasonal control of implantation. Actual birth weight is as predicted from an interspecific comparison of ungulates. The data imply either that there is an obligate period of embryonic diapause, irrespective of season, or that postimplantation fetal growth rate is slow compared with that in other deer species.