Influence of ovarian dynamics and circulating steroid hormones on OPU-IVEP outcomes in Holstein heifers.

In bovine in vitro embryo production (IVEP), optimizing oocyte quality and yield per donor serves as the cornerstone for improving blastocyst development and field efficiency. This study evaluated the impact of naturally occurring ovarian structures on follicular dynamics, oocyte quality, and embryo development during random-day ovum pick-up (OPU) in Holstein heifers (n = 78). Donors were divided into three groups based on ovarian patterns: Group I (corpus luteum [CL]; n = 43), Group II (only antral follicles [AF]; n = 20), or Group III (CL + dominant follicle [CL + DF]; n = 15). Follicles (3-8 mm) were aspirated, and serum progesterone (P4) and estradiol (E2) levels were measured. Group I had a significantly higher usable (A + B+C) oocyte count (7 vs. 3) and total oocyte count (10 vs. 5) than Group III (P < 0.05). The mid-sized follicle pool was lower in Group III than in Group II (11 vs. 13; P < 0.05). Mature oocytes, cleaved zygotes, and blastocyst counts were significantly lower in Group III than in Groups I and II (P < 0.05). Group I achieved a higher cleavage rate than Group III (77.60 vs. 62.06; P < 0.05). Crucially, the blastocyst formation rate was significantly higher in Groups I (49.59%) and II (45.45%) than in Group III (22.20%; P < 0.05). On the OPU day, donors with serum P4 > 1 ng/mL exhibited a higher yield of B-quality oocytes than did those with P4 < 1 ng/mL (1.5 vs. 1.0; P < 0.05). In conclusion, a dominant follicle during random-day OPU is closely associated with a lower antral follicle pool, compromised oocyte quality, and reduced embryo development. Consequently, avoiding active follicular dominance during donor management might represent a supportive strategy to optimize IVEP efficiency under commercial field conditions.