146 Relationship between preovulatory follicle maturity and the follicular fluid metabolome

Improving reproductive efficiency has been a large focus of the livestock industry over the past few decades. Although numerous factors play a role in reproduction, oocyte competence for embryo development is essential for pregnancy establishment. The preovulatory follicle’s metabolite milieu is critical for nourishing and supporting the oocyte as it prepares for maturation, fertilization, and early embryo development. Previous research demonstrated that physiological maturity of preovulatory follicles at the time of gonadotrophin-releasing hormone (GnRH) administration to induce the LH surge, was related to the follicular fluid metabolome and oocyte competence for embryo development. Such studies focused on follicle maturity at GnRH administration and its relationship with follicular fluid metabolites at a later time point during oocyte maturation. However, no studies have examined a real-time relationship between preovulatory follicle maturity before GnRH administration and the follicular fluid metabolome at this earlier time point. Cellular differentiation and metabolic function vary drastically in follicular components pre- and post-GnRH. Understanding of the intrafollicular milieu of preovulatory follicles before GnRH and its relationship to follicle maturity are essential next steps in understanding preovulatory follicle–oocyte relationships that promote fertility. We hypothesized that follicle maturity would be associated with the pre-GnRH preovulatory follicular fluid metabolome. Beef cows (n = 69) underwent a 7-day CO-Synch protocol. Fifty hours after prostaglandin F_2α administration, follicular fluid from the largest estrogen-active follicle (8.7–15.4 mm) was collected using transvaginal ultrasound guided aspiration. Follicle maturity was assessed using estradiol concentration in serum at the time of follicle aspiration. The follicular fluid metabolome was determined using ultra-high performance liquid chromatography–high resolution mass spectrometry. A multiple linear model was designed to assess relationships between abundance of each metabolite and serum estradiol concentration. There were 125 metabolites detected in the preovulatory follicular fluid, of which 44 metabolites were negatively associated and one was positively associated with serum estradiol concentration (P < 0.05). Many of the metabolites associated with serum estradiol were involved in purine, pyrimidine, and arginine metabolism (pathway enrichment FDR < 0.1). It is possible that before the LH surge, the metabolite usage-to-production ratio is increased in the granulosa cells and the cumulus–oocyte complex in follicles of greater maturity, thereby leading to reduced abundance of metabolites. Increased uptake of metabolites may contribute to superior follicular preparation for granulosa cell differentiation, cumulus expansion, and oocyte maturation. Future efforts to relate these findings with granulosa cell function or oocyte competence will determine if differences in follicular fluid milieu are equally impactful at this time point as previously observed in samples collected after the LH surge.

This project was supported by Agriculture and Food Research Initiative Competitive Grant no. 2023-67015-39454 from the US Department of Food and Agriculture.