Embryo transfer after synchronization of ovulation using CIDR and GnRH for recipient beef cows

The present study was to investigate the effect of two programs for synchronization of ovulation on embryo transfer in recipient beef cows. GnRH-PGF2a-GnRH protocol (Ovsynch: GnRH program, n=19), and CIDR-PGF2a-GnRH protocol (CIDR program, n=20) in which the first GnRH administration in Ovsynch is replaced by administration of progesterone (P) using a controlled intravaginal drug release device (CIDR) were compared. Two synchronization programs were started at an appropriate day of estrous cycle. GnRH program was performed according to Ovsynch. On the other hand, in the CIDR program, CIDR was detained in a vagina for 12 days, PGF2a was administered at the time of CIDR removal, and then GnRH was given at 48 h after PGF2a. Fresh embryos obtained from Japanese Black cows 7 days after GnRH administration following PGF2a in both programs were transferred to surrogate mother. The period of estrus was 48-72 h after administration of PGF2a in 69.2% of the cow in GnRH program and in 85.7% of the cow in CIDR program. Especially, estrous expression in CIDR program could be inhibited till 48 h after PGF2a. It may be possible that the timing of embryo transfer in CIDR program is fixed on Day 7 after GnRH (Day 0) which had been administered 48-72 h after PGF2a. Estrus was not induced in 26.3% of cows in GnRH program from the result of plasma progesterone (P) concentration at the second GnRH injection. Corpus lutea (CL) formed in CIDR program was estimated at either Good (40%) or Fair (60%) grade at an embryo transfer, while Poor grade of CL existed in 10.5% of cows in GnRH program. Conception rates in GnRH and CIDR programs were 68.8% and 82.4%, respectively. Moreover, conception rate of anestrous cows in CIDR program (n=5) was 100%. These results showed that CIDR-PGF2a-GnRH program for recipients was effective for estrus induction, synchronization of ovulation, and pregnancy rate as well as in Ovsynch program. In addition, the shift to follicular phase at GnRH injection in CIDR-PGF2a-GnRH program was shown in many cows, judging from the result of P concentration. Also, CIDR-PGF2a-GnRH protocol had tendency to induce formation of good quality of CL and conception at high rate. Consequently, in the CIDR-PGF2a-GnRH protocol for recipient, the program is able to start at anytime in estrous cycle, estrous expression could be inhibited during the treatments, and the recipients showed ovulation for a restricted period of estrus after die treatments. The present study revealed that CIDR-PGF2a-GnRH protocol was useful method for improving conception rate for embryo transfer.