131 The effects of dominant follicle removal on quality of cumulus-oocyte complexes in half-blood Bos indicus × Bos taurus donor cattle

The effect of dominant follicle removal (DFR) on oocyte quality in Bos taurus cattle has been documented, but the results in half-blood B. taurus and B. indicus is largely unknown. In general, B. indicus cattle produce more follicles and have more follicular waves during the oestrous cycle. The time interval of onset of oestrus to ovulation is shorter in B. indicus than in B. taurus. Therefore, the interval of follicle regeneration following DFR occurs sooner in B. indiucs than in B. taurus. Current literature of B. taurus studies the effects of DFR before ovum pick-up (OPU) coupled with super stimulation, however, there are no reports on the impacts of DFR in non-super stimulated B. indicus. We hypothesise that DFR will produce cumulus-oocyte complexes (COCs) of greater quality in half-blood Holstein (B. taurus) and Gyr (B. indicus). A group of 36 cyclic donors (age 24–40 months.) were randomly assigned non-DFR (control, n = 35) or DFR (n = 80) over the course of three separate replicates. Ovaries of cows in the DFR group were examined by ultrasonography at random stages in the oestrous cycle, and the largest follicle (avg. 8–10.5 mm) was aspirated transvaginally using OPU methods (defined as Day 0). Both control and DFR group donors were randomly selected to undergo traditional OPU aspiration either 48 or 72 h after Day 0. COCs were graded within 5 min of collection. Grading of COCs followed IETS guidelines, with quality I, II, and II being viable (descending order of grade) and IV being dead. A generalised linear model and chi-squared tests were used to investigate the association between COC quality and treatment (DFR or control). Data are reported as odds of oocyte quality collected to treatment (DFR vs control), with ≥1 being high and <1 being low. The results indicate that the odds of COC quality I and II (relative to quality II and IV) are significantly (P < 0.007) lower (0.584) for control compared to DFR as well as the odds of COC quality I, II, and III (relative to IV) (P < 0.045). The odds of COC quality I (relative to II, III, and IV) was lower (0.082) in control compared to DFR (P < 0.082.) Of the 2569 COC collected, 71.6% in the DFR group had quality I and II while 28.04% in the control group had comparable quality. We conclude that performing DFR in half-blood B. taurus × B. indicus cattle is beneficial for the development of higher quality COC.