The aim of this study was to assess the effect of follicular size on estradiol (E₂) and progesterone (P₄) levels in intrafollicular fluid, ATP content in oocytes, and the embryo development rate in prepubertal sheep. Slaughterhouse ovaries were dissected to recover the follicles, which were classified according to the follicle diameter as <3 mm (n = 20) and ≥3 mm (n = 17). Then, follicular fluid was obtained and analyzed by radioimmunoassay to determine the E₂ and P₄ concentrations. Another group of ovaries was used to recover cumulus-oocyte complexes according to follicle size. In vitro maturation (IVM), in vitro fertilization (IVF), and embryo culture were performed using standard procedures, and ATP level was assessed at 0 and 24 h of IVM. Intrafollicular concentrations of E₂ and P₄ and E₂:P₄ ratio were higher in ≥3 mm (18.7 ± 5.9 ng/mL, 7.8 ± 1.2 ng/mL, and 3.6 ± 1.3, respectively) than <3 mm (1.8 ± 0.4 ng/mL, 2.6 ± 0.3 ng/mL and 0.9 ± 0.3, respectively) follicles. The rate of ATP increased during IVM and was higher in oocytes from ≥3 mm than <3 mm (22.4 ± 0.7 and 8.6 ± 2.2-fold change; respectively) follicles. After IVF, the blastocyst development was higher in oocytes recovered from ≥3 mm (11.1 ± 0.9%) than from <3 mm (6.5 ± 0.7%) follicles. These results indicate an improvement in the competence and development of oocytes from ≥3 mm follicles with a higher E₂:P₄ ratio. Thus, this ratio could be used as reference to design IVM medium and to enhance the in vitro embryo production in lambs.

本研究的目的是评估卵泡大小对卵泡液中雌二醇 (E ₂ ) 和孕酮 (P ₄ ) 水平、卵母细胞中 ATP 含量以及青春期前绵羊胚胎发育率的影响。解剖屠宰场卵巢以回收卵泡，根据卵泡直径分为<3 mm（n = 20）和≥3 mm（n = 17）。然后，获得卵泡液并通过放射免疫分析法测定E ₂和P ₄浓度。另一组卵巢用于根据卵泡大小回收卵丘-卵母细胞复合物。使用标准程序进行体外成熟 (IVM)、体外受精 (IVF) 和胚胎培养，并在 IVM 0 和 24 小时评估 ATP 水平。_{E 2}和 P ₄和 E ₂的滤泡内浓度：P ₄≥3 mm（分别为 18.7 ± 5.9 ng/mL、7.8 ± 1.2 ng/mL 和 3.6 ± 1.3）的比率高于 <3 mm（1.8 ± 0.4 ng/mL、2.6 ± 0.3 ng/mL 和 0.9 ± 0.3，分别）卵泡。IVM 期间 ATP 的速率增加，并且在≥3 mm 的卵母细胞中高于 <3 mm（分别为 22.4 ± 0.7 和 8.6 ± 2.2 倍变化）卵泡。体外受精后，从≥3 mm (11.1 ± 0.9%) 恢复的卵母细胞的囊胚发育高于从 <3 mm (6.5 ± 0.7%) 卵泡恢复的卵母细胞。这些结果表明具有较高 E ₂ :P ₄比率的≥3 mm 卵泡的卵母细胞的能力和发育有所改善。因此，该比率可用作设计 IVM 培养基和提高羔羊体外胚胎产量的参考。