Effect of CIDR-based protocols for timed-AI on the conception rate and ovarian functions of Japanese Black beef cows in the early postpartum period

Our objectives were to compare: (1) conception rates (in early postpartum Japanese Black beef cows) to timed-artificial insemination (timed-AI) among Ovsynch and Ovsynch plus CIDR protocols, and a protocol that used estradiol benzoate (EB) in lieu of the first GnRH of the Ovsynch plus CIDR; and (2) the effects of these protocols on blood concentrations of ovarian steroids. Cows in the control group (Ovsynch; n = 35) underwent a standard Ovsynch protocol (GnRH analogue on Day 0, PGF2α analogue on Day 7 and GnRH analogue on Day 9), with timed-AI on Day 10, approximately 20 h after the second GnRH treatment. Cows in the Ovsynch + CIDR group (n = 31) received a standard Ovsynch protocol plus a CIDR for 7 days (starting on Day 0). Cows in the third treatment group (EB + CIDR + GnRH; n = 41) received 2 mg of EB on Day 0 in lieu of the first GnRH treatment, followed by the same treatment as in the Ovsynch + CIDR protocol. The conception rate tended to be greater in the Ovsynch + CIDR group (67.7%, P < 0.15) and was greater in the EB + CIDR + GnRH (73.2%, P < 0.05) and CIDR-combined (both CIDR-treated groups were combined) groups (70.8%, P < 0.05) than in the Ovsynch group (48.6%). Plasma progesterone concentrations were higher on Day 7 (P < 0.01) and lower on Days 14, 17 and 21 (P < 0.001) in the CIDR-combined group than in the Ovsynch group. Plasma estradiol-17β concentrations were higher on Day 7 in the Ovsynch group of non-pregnant cows than in the CIDR-combined group of non-pregnant cows and in an all-combined group (all treatment groups combined) of pregnant cows (P < 0.01). Furthermore, estradiol-17β concentrations were lower on Day 9 in the Ovsynch and CIDR-combined groups of non-pregnant cows than in the all-combined group of pregnant cows (P < 0.05). In conclusion, both protocols using CIDR improved conception rates following timed-AI in early postpartum suckled Japanese Black beef cows relative to the Ovsynch protocol. Treatment with a CIDR may prevent early maturation of follicles observed in non-pregnant cows treated with the Ovsynch protocol, by maintaining elevated blood progesterone concentrations until PGF2α treatment.