130 Effect of the day of dominant follicle removal on ovum pick-up success on ½ Holstein × ½ Gyr cows

Follicular wave synchronisation by dominant follicle removal (DFR) has shown a positive impact on ovum pick-up (OPU) outcomes. However, Bos taurus and Bos indicus cattle show significant variation in oestrus cycle patterns. In addition, there is a lack of data reporting the recommended interval between DFR and OPU exclusively (with no exogenous hormone administration). This absence of data is even more evident when considering crossbred (Bos taurus × Bos indicus) cattle. Therefore, with the aim of improving OPU success, this study evaluated the influence of timing of DFR on the quality of cumulus-oocyte complexes (COCs) recovered. For this study, half-sibling 1/2 Holstein × 1/2 Gyr cyclic cows, 24 to 40 months old and raised in a similar environment, were used. The animals had their largest follicle (avg. 8–10.5 mm) removed by OPU (Day 0) at random days of the oestrus cycle. The donors were split into two groups Day −2 and Day −3 and underwent OPU ∼48 h (Day −2) or 72 h (Day −3) later. Following the OPU, the COCs were evaluated and graded based on morphological characteristics and split into four groups: grades I, II, III, and IV. Grade I was the highest quality COCs, and grade IV was the degenerated COCs. The experiment consisted of three replicates where the majority of the animals were reused within a 4-week interval. A total of 78 OPUs (37 on Day −2 and 41 on Day −3) were performed, resulting in 1809 COCs recovered (932 on Day −2 and 877 on Day −3). Generalised linear models and chi square contingency tables were used to assess the effect of day on the COC quality. The results indicate that day of removal had a significant (P < 0.01) effect on the quality of COC recovered after DFR. The percentage of COCs with grades I and II relative to III and IV was significantly (P < 0.0002) higher on Day −2 compared to Day −3 (odds ratio: 2.456). Although 62.44% of the COC were grade I and II on Day −2, 37.56% had comparable quality on Day −3. Therefore, the application of DFR technique on 1/2 Holstein × 1/2 Gyr cows 2 days previous to OPU positively affects the quantity and quality of COCs recovered compared to COCs recovered at 3 days post-DFR. In conclusion, a shorter interval of OPU following DFR in Bos taurus × Bos indicus cattle increases the number of higher quality COCs.