Periodicity of Ovarian Follicular Dynamics in Postpartum Cows Demonstrated Using Time-Series Analysis Based on the Maximum Entropy Method

抄録

A specific decrease in the number of ultrasonographically identified follicles (uiFOL) in Japanese Black cows at 92 to 98 days after parturition had previously been reported. In the present study, the number of uiFOL in cows was observed until 500 days postpartum by an ultrasonic wave technique. The observation results showed that there are two specific decrease periods at about 303 to 308 days and 495 to 500 days after parturition. Also when superovulation treatments were done at these periods, many transferrable embryos were recovered. Therefore, these periods well resembled the previously reported decrease of uiFOL and embryo production at 92 to 98 days. To elucidate whether or not the variation of uiFOL including the specific decrease period resulted from a phenomenon with multiple periodicity or random variation, the ovarian follicular dynamics for 14 to 500 days after parturition were analyzed using the spectral analysis method based on the maximum entropy method (MEM). The variation in the number of uiFOL was constituted of a distinct periodic structure in each cow. In addition, the frequency distribution of the values estimated by MEM spectral analysis was investigated. As a result, five peaks were identified and a peak of 0.045 corresponded to 21 days postpartum. The other three peaks except for 0.03 corresponded to multiples of 21 days. Accordingly, the frequency distribution demonstrates that ovarian follicular dynamics is based on a 21-day cycle, and that it starts from parturition day.