Variation in gestation length among captive reindeer ( Rangifer tarandus tarandus)

• Published in: Theriogenology 2009-07, Vol.72 (2), p.190-197
• Main Authors: Rowell, J.E., Shipka, M.P.
• Format: Article
• Language: English
• Subjects: Animals; Body Weight; Breeding; calving; Calving synchrony; captive animals; conception; embryogenesis; Estrous Cycle; estrus; estrus synchronization; Female; female reproductive system; Fertilization; Gestation length; gestation period; Gestational Age; Male; natural mating; ovulation; periodicity; Photoperiod; Pregnancy; Progesterone - blood; Rangifer tarandus; Regression Analysis; Reindeer; Reindeer - physiology; seasonal variation; Seasons; temporal variation; Time Factors; wild animals
• ISSN: 0093-691X; 1879-3231
• DOI: 10.1016/j.theriogenology.2009.01.022

An estimated 90% of reindeer females are mated in a 10- to 21-d interval and give birth in an equally synchronized manner. Reported gestation length in reindeer is highly variable (range, 203 to 240 d), almost twice the reindeer estrous cycle length. Previously, we identified a significant, negative relationship between gestation length and conception date in a small group of reindeer. In the current study, the negative relationship was investigated in a switchback design, where reindeer were divided into two groups synchronized for early and late mating over a 2-yr trial. Regression analysis of 11 paired observations produced a negative ( P < 0.001) association between gestation length and conception date (slope = − 0.31). Dam weight at breeding and prior to parturition, calf birth weight, and calf sex were not significant variables in the regression. Regression analysis of a larger data set from two University of Alaska Fairbanks reindeer herds, where conception date (verified by systemic progesterone) and gestation length were recorded (historical data set), supported previous conclusions ( n = 70; slope = −0.37; P < 0.001). Although the calf sex ratio did not differ with gestation length, there was a positive relationship ( r 2 = 0.19; P = 0.014) between male birth weight and gestation length in the larger data set. The negative relationship between conception date and gestation length enhanced calving synchrony, though the limits of gestation plasticity and underlying mechanisms are not clear. The potential role of photoperiod on early embryonic development is discussed.