Influence of the corpus luteum on cumulus-oocyte complexes competence in equines

This study evaluated the effect of the presence and location of the corpus luteum (CL) on quantity and competence of equine cumulus-oocyte complexes (COCs). Pairs of ovaries were collected at the slaughterhouse and classified into three groups: ovaries with CL (CL+); ovaries with CL in the contralateral ovary (CL-) and ovaries without a CL (NCL). Were evaluated COC quantity, morphology, nuclear maturation rate, and intrafollicular progesterone concentration and gene expression (BAX, BMP-15, ODC1, GDF9, AURKA) in both cumulus cells and oocytes after in vitro maturation. Results showed a lower recuperation of COCs from CL+ (2 ± 0.9) compared to NCL (4.9 ± 0.8), but not different from CL- (3.5 ± 0.8). Morphologically, COCs from CL- exhibited a higher proportion of expanded cumulus cells (74.4 %) in relation to CL+ and NCL groups (10 % and 13.1 %). However, the proportion of COCs reaching metaphase II after in vitro maturation was higher in CL+ group (58.3 %) compared to NCL (42 %) and did not show differences in relation to CL- group (47,2 %). Additionally, CL+ group showed higher intrafollicular progesterone concentrations compared to NCL, but not different from CL- (574, 485 and 392 ng/mL for CL+, CL- and NCL groups, respectively). Finally, BMP-15 in oocytes and GDF9 in cumulus cells were higher in COCs from animals with CL (CL+ and CL-) in relation to NCL group. These findings suggest a potential association between CL presence, intrafollicular progesterone concentration, and the expression of cell quality genes in equine COCs, contributing to enhanced rates of oocyte nuclear maturation.