Follicular fluid during individual oocyte maturation enhances cumulus expansion and improves embryo development and quality in a dose-specific manner

We evaluated the effect of supplementation of different concentrations of bovine follicular fluid (FF) during in vitro maturation (IVM) on oocyte development and blastocyst quality in group and individual culture conditions. To do so, in vitro maturation medium (TCM-199 with 20 ng/mL epidermal growth factor and 50 ttg/mL gentamycin) was supplemented with 0 (control), 1, 5, or 10% of FF. Follicular fluid was collected from slaughterhouse-derived ovaries, selecting follicles between 12 and 20 mm in diameter. Oocytes were either produced in groups or individually matured, fertilized, and cultured to the blastocyst stage, allowing for separate follow-up of each oocyte. Development (cleavage and blastocyst rates) among experimental groups were fitted in mixed-effects models, and blastocyst quality parameters (assessed via differential apoptotic staining) were evaluated in mixed linear regression models. We also assessed the cumulus expansion (prior and after maturation) for individual culture conditions, and their difference was fitted in mixed linear regression models. The FF was collected from two batches, with an estradiol/progesterone ratio higher than 1. The FF batch did not affect the development or blastocyst quality in group or individual culture conditions (P> 0.05). In group culture, development was similar among experimental groups (P> 0.05). Five or 10% of FF supplementation improved (P < 0.05) aspects of blastocyst quality such as total cell numbers (TCN), trophectoderm (TE), inner cell mass (ICM), and ICM/TCN and apoptotic cells/TCN ratio in comparison to control. In the individual culture system, 5% FF supplementation increased (P < 0.05) day 8 blastocyst rate (33 +/- 3.4% (LSM +/- SE)) in comparison to control (20 +/- 2.7%) and 1% FF supplementation (19 +/- 2.6%) but it was not different (P > 0.05) from 10% FF supplementation (28 +/- 3.4%). Five percent of FF supplementation resulted in greater TCN, ICM, and ICM/TCN than control (P < 0.05). It also resulted in a greater expansion of cumulus cell investment than the other groups (P < 0.05), with a 3-fold increase compared to control. In conclusion, 5% of FF supplementation during IVM improved the cumulus expansion and the blastocyst development and quality in an individual culture system. However, FF supplementation during maturation in a group culture system did not increase development, but it modestly improved some embryo quality aspects when 5 or 10% of FF was added. (C) 2021 Elsevier Inc. All rights reserved.

Automated summary

The study evaluated the effect of adding different concentrations of bovine follicular fluid on oocyte maturation and blastocyst quality, showing that supplementation of 5% FF improved cumulus expansion and blastocyst development and quality in an individual culture system.