Effect of CIDR Treatment at Day 16 of Estrous Cycle on Follicular Growth in Dairy Heifers with Two or Three Follicular Waves

Abstract

To show the effect of intravaginal progesterone-releasing device (CIDR) on turnover of DF and follicular growth after CIDR insertion on day 16 of estrous cycle and to compare the follicular growth during CIDR treatment between heifers with two or three follicular waves, four heifers were given CIDR for 7 days at late luteal phase on day 16 of estrous cycle. The presence of CIDR in the vagina containing progesterone prevented for the animals to return to estrus at the normal time and significantly increased cycle length, as compared to the preceding cycle (26.3 ±0.5 vs 20.8 ±1.5 days, p<0.05). Ovarian follicular dynamics were characterized by waves of follicular development occurring at different times during the estrous cycle. In the stage 1, four heifers had two (n=2) or three (n=2) follicular waves per estrous cycle. However, during the cycle of CIDR treatment, all heifers had three follicular waves per cycle. The CIDR treatment caused an extension of dominant phase of the ovulatory DF selected in the third follicular wave in heifers with 3 follicular waves per cycle before CIDR treatment. In heifers with two follicular waves per cycle before CIDR treatment, after CIDR treatment the DF underwent atresia without delay and followed emergence of the new follicular wave, in which no extension of dominant phase of the DF or ovulatory follicle was shown. The CIDR treatment did not affect the follicular growth during the subsequent cycle. In conclusion, when CIDR treatment commenced at late luteal phase, CIDR may cause an extension of an interval from emergence to ovulation of ovulatory DF in heifer with three follicular waves. And also, the CIDR treatment does not delay atresia process of DF in preceding cycle and is developed the new follicular waves in heifers with two follicular waves per cycle before CIDR treatment