Follicular fluid secretome enhances the meiotic competence of in vitro matured equine oocytes, but not the developmental competence of zygotes after intracytoplasmic sperm injection (ICSI)

: In vitro embryo production is widely used in equine clinical reproduction; however, its efficiency remains suboptimal due to the undermined developmental competence of in vitro-matured oocytes. In this work, we evaluated the effect of mare preovulatory follicular fluid (PFF) secretome supplementation during in vitro maturation (IVM) of equine oocytes recovered post-mortem. Secretome was isolated from PFF and was added to the IVM medium at concentrations of 20 µg/ml (S20) or 40 µg/ml (S40). The percentage of mature oocytes, as well as embryo cleavage, blastocyst development, and gene expression of embryos produced by intracytoplasmic sperm injection (ICSI) was analysed. Gene expression of embryos at day 7 post-ICSI was analysed by real-time quantitative PCR. We observed that the addition of PFF secretome at 40 µg/ml (S40) significantly increased oocyte maturation rates (Control vs. S40: 35.4 ± 3.6 % vs. 46.5 ± 2.7 %; mean % ± SEM; P < 0.05) and reduced the proportion of degenerated oocytes after maturation (Control vs. S40: 58.6 ± 4.2 % vs. 44.0 ± 4.8 %; P < 0.05) compared to the control group. However, no effects were observed on cleavage or blastocyst rates, nor on the expression of the candidate genes studied, namely BEX2, FABP3, ODC, MOBKL3, HSP90AA1, BAX and BCL2. In conclusion, supplementation of PFF secretome during IVM at 40 µg/ml, but not at 20 µg/ml, improves the meiotic competence of post-mortem retrieved equine oocytes but does not influence their developmental competence or the expression of the selected genes in the resulting embryos.