202 Effects of fatty acid binding protein in the maturation medium of bovine oocytes on in vitro development

Efficient cattle production is vital for meeting demand while maximizing profitability and sustainability. Although in vitro embryo production addresses genetic and financial challenges for producers, blastocyst development rates remain suboptimal. Maturation of oocytes is the first, crucial stage of in vitro embryo production. Research indicates that IVM oocytes typically have higher lipid content. Fatty acid binding protein (FABP) is thought to mediate transport of lipids and fatty acids between oocytes and cumulous cells via transzonal projections. The aim of this study was to investigate whether differences occurred in the cleavage and blastocyst development rates of embryos from oocytes matured with varying concentrations of FABP-3 in the maturation medium. Oocytes were collected from seven Jersey cows via transvaginal aspiration every 3 days for five collection sessions. Selected oocytes were randomly placed in either maturation control drops or drops supplemented with FABP-3 at concentrations of 10 or 20 μg mL⁻¹ (10–15 per 50-μL drop). Matured oocytes were co-incubated with sperm cells in 500-μL wells. In total, 234 presumptive zygotes were vortexed to remove cumulus and placed into culture (10–15 per 50-μL drop). IVM (18–20 h), fertilization (18–20 h), and culture were performed under an oil overlay at 38.5°C in a fully humidified 5% CO₂, 5% O₂, 90% N₂ environment. On the seventh day of culture, the cleavage (≥2 cells) and blastocyst development was evaluated, and the rates were calculated from the total number of ova in culture. Chi-square tests were used to evaluate the binary outcomes (achieved development stage or not). Results indicated that cleavage rates were significantly higher in the control and 10 μg mL⁻¹ groups (75.0% ± 5.0 and 64.6% ± 5.4, respectively) compared with the 20 μg mL⁻¹ group (32.9% ± 5.3). There was no significant difference between the 10 μg mL⁻¹ group and controls. Blastocyst development rates were significantly higher in the controls (34.2% ± 5.4) compared with the 20 μg mL⁻¹ group (10.1% ± 3.4). No significant difference in blastocyst rates were detected between the 20 and 10 μg mL⁻¹ groups (20.2% ± 4.5) but controls tended (P = 0.07) to be higher than the 10 μg mL⁻¹ group. Supplementation with 20 µg mL⁻¹ of FABP significantly impaired both cleavage and blastocyst development. It is unclear whether FABP from the medium can cross the cell membrane to enter the oocyte or if a higher concentration of FABP attracts more lipid. Two hypotheses exist: FABP from the medium may enter the oocyte and lead to excessive lipid accumulation, or FABP may remain in the medium and sequester lipids from the oocyte. Lipids, an essential energy source for oocyte function and development, must be carefully regulated. Excess lipid content can lead to increased oxidative stress and metabolic imbalances. Therefore, maintaining a balance is crucial to support oocyte needs without causing detrimental effects. Further research is needed to determine the optimal concentration of FABP supplementation and uptake by the oocyte and associated lipid management. Although this study identifies a potential upper limit, the effects of lower FABP concentrations still need to be explored.