Resumen
- The quality of oocytes is more critical for the success of bovine in vitro embryo production (IVP) than the conditions of in vitro culture of these structures. Despite knowledge about bovine follicular development, especially gonadotropin-dependent phase, be considerably wide, knowledge about effects of the estrous cycle phase, follicular or luteal, on recovery of oocytes may strongly contribute to improve IVP efficiency. Previous efforts to find the proper cumulus-oocyte complex (COC) in vitro maturation conditions did not improve this technique at level of the in vivo embryo production. In physiological conditions the oocyte to be fertilized is donated by healthy follicles during a specific stage of the estrous cycle. However, COCs collected for IVP are obtained from follicles disregarding the follicular phase; consequently, they may have been subjected to different levels of estradiol, progesterone, FSH and LH. Plasma progesterone affects oocyte quality probably because it allows the follicle is exposed for a long period to low amplitude LH pulses, resulting in good quality oocyte. Besides, the presence of a functional corpus luteum (CL) in the ovary may interfere with the amount and quality of oocytes, CL is related to a high vascularization of the ovary which can propitiate an optimal hormonal and nutritional environment for developing follicles. Moreover, the developmental ability of oocytes from small follicles can be influenced by a presence of dominant follicle. Therefore, the ovarian condition of regularly cyclic females needs to be a concern in collection of oocytes for commercial IVP