The effects of age, body weight and reproductive status on conception dates and gestation periods in captive sika deer

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Variation in the parturition dates of captive sika deer (Cervus nippon) are explained by factors affecting conception date and gestation period. The timing of conception was related to lactational status, and all non-lactating females conceived before the median conception date. Young females were more likely to conceive after the median date of the conception than older females. Gestation period was not related to the fawns sex or the females age. No relationship between gestation period and female body weights was detected in 2000–2001, while an inverse relationship was observed in 1999–2000, a year with heavy snowfall. Conception dates explained most variations in parturition dates in 2000–2001, but gestation periods as well helped explain variations in 1999–2000. We propose that females in poor body condition compensate for poor fetal growth with an extended gestation period after a severe winter. Estimates of conception dates from fetal age or parturition dates should consider these complicating factors.