193 Effect of dominant follicle removal before ovum pickup in Girolando cattle

Dominant follicle removal (DFR) is known to synchronize the follicular wave, inducing an FSH surge and follicular growth. Besides that, oocytes recovered from more developed follicles have greater competency, improving in vitro embryo production. However, little is reported about the response of Girolando cattle to DFR, considering the different breed composition. Herein, we characterised the ovarian response to this technique and aimed to identify the preferred interval DFR-ovum pickup (OPU) for 1/2 Girolando and 1/4 Girolando donors (36.09 ± 7.79 and 21.96 ± 1.32 months old, respectively) when performed at random days of the oestrous cycle. Animals were randomly assigned to three groups at the beginning of the experiment (Day 0), one control (no DFR), which was equally split for OPU on Day 2 and Day 3; one DFR 48 h (OPU on Day 2); and one DFR 72 h (OPU on Day 3). On Day 0, all animals had their ovarian follicular population evaluated by ultrasound scanning, and the donors in the DFR groups had their follicles ≥5 mm aspirated. On Day 2, one of the control groups and the DFR 48 h group underwent ovarian scanning. Their follicular population was counted by size (small, <3 mm; medium, 3–6 mm; and large, >6 mm), followed by OPU and subsequent grading (G I–IV) of the COCs recovered. On Day 3, the other control group and the DFR 72 h underwent the same steps. A MIXED procedure of SAS was used to analyse the effect of treatment (DFR-OPU interval), breed composition, and the interaction of treatment and breed composition. Age is fitted in the model as a covariate, and random effects were donor and the interaction of donor, period of the year, and year. From 235 observations, 212 were used for the analysis since, on Day 0, not all animals had ≥5 mm follicles considering the three groups. The results show that DFR applies to ≈90% of donors when randomly assigned. The results are presented as LSM ± s.e.m. The DFR 48 h and 72 h groups had a greater (18.39 ± 1.42 and 14.98 ± 1.42, respectively, P < 0.01) number of medium-size follicles (more developed) compared with the control group (10.84 ± 1.42) at OPU. Furthermore, there was a greater number of highest quality COCs (G I, 2.09 ± 0.31, P = 0.004) from OPU with a 48-h interval than from DFR 72 h (1.11 ± 0.31) and control (0.92 ± 0.31). In addition, 1/2 Girolando had significantly greater medium and total follicles and G IV COC than 1/4 Girolando (18.3 ± 2.02, 33.34 ± 2.67, 5.52 ± 0.64, and 11.35 ± 2.02, 22.56 ± 2.67, 0.77 ± 0.64, respectively). There was no significant effect of treatment and breed composition interaction. Therefore, 1/2 Girolando have a greater count of total and more developed follicles and of lowest quality COC than 1/4 Girolando, although they respond similarly to DFR. In conclusion, the introduction of DFR before OPU on 1/2 and 1/4 Girolando has advantageous effects on OPU yields, promoting the aspiration of more developed follicles and better-quality oocytes when performed 48 h in advance.