Ayala Guanga, Luis EduardoSamaniego Campoverde, Jorge XavierArgudo Garzón, Daniel ErnestoPerea Brugal, Mariana SofiaPerea Ganchou, Fernando PedroRodas Carpio, Ermes RamiroNieto Escandón, Pedro Emilio2021-01-122021-01-1220201609-9117https://revistasinvestigacion.unmsm.edu.pe/index.php/veterinaria/article/view/17571The aim of this study was to evaluate the effects of gonadotropin treatment and the interval between ovarian stimulation with FSH/LH and the follicular aspiration session, on the quantity and quality of the cumulus oocyte complexes (COCs) obtained by ovum pick up (OPU)) in Ecuadorian Creole heifers. Four heifers were randomly assigned to four groups (FHS/LH 40h; FSH/LH 48h; control 40h; control 48h). In two groups a dose (0.011 mg, IM) of GnRH was applied on day 0, followed by 500 IU, IM, of FSH/LH on day 2, and the OPU session at 40 (FSH/LH 40 h) or 48 hours (FSH/LH 48h) after the application of gonadotropin. In the other two groups, FSH/LH was replaced by a physiological solution. There was no statistical difference in the recovery rate of COCs between FSH/LH 40h and FSH/LH 48h, but approximately twice as many COCs (p<0.05) were obtained than in those who did not receive ovarian stimulation. In addition, 2.4 times more COCs of quality A were achieved in the treatment of FSH/LH 48h than in that of FSH/LH 40h. All (100%) of these structures reacted positively to Brilliant Cresyl Blue (BCB+), which means that they finished the growth and were competent to initiate in vitro maturation. It is concluded that the treatment with FSH/LH 48h allowed to obtain a greater number of COCs competent for in vitro maturation.es-ESFollicular aspirationCOCsOvarian stimulationBrillant cresyl blueARTÍCULO10.15381/rivep.v31i1.17571