Differential metabolome profiles in preovulatory follicular fluid of cattle with varying duration of proestrus

Critical developmental processes that promote optimal fertility occur in both the cumulus-oocyte complex and intrafollicular environment during proestrus. Previous studies have demonstrated that shorter periods of proestrus are associated with decreased pregnancy rates in bovine females undergoing fixed-time artificial insemination or displaying estrus. The follicular fluid metabolome contains both starting and by-products of follicular cell metabolism, and alterations in follicular fluid metabolome have been associated with oocyte developmental competence. Changes in the follicular fluid composition throughout proestrus may play an important role in determining oocyte competence for successful embryo development and pregnancy. We hypothesized that length of proestrus would influence the metabolome profiles in bovine preovulatory follicular fluid. Therefore, we performed a study with the objective to profile the follicular fluid metabolome of preovulatory follicles at estrus and determine if length of proestrus was related to metabolite abundances within the follicular fluid. Follicular fluid was collected via transvaginal follicle aspiration from cows at the onset of estrus (n = 17). The follicular fluid then underwent Ultra-High Performance Liquid Chromatography-High Resolution Mass Spectrometry for metabolomic analysis. We identified eighty-five metabolites across follicular fluid samples. The metabolites ‘homocysteine’, ‘methionine sulfoxide’, ‘n-acetyl-beta-alanine’, ‘trehalose/sucrose’, and ‘glycine’ were determined to be positively related to length of proestrus (false discovery rate (FDR) < 0.10). Homocysteine and methionine sulfoxide are indicators of the presence of reactive oxygen species (ROS), while trehalose and glycine possess antioxidant properties to combat overaccumulation of ROS. Reactive oxygen species play an essential role in both ovulation and cumulus expansion, but their abundance must be maintained within levels required for an oxidatively balanced environment during oocyte maturation. Increased abundance of metabolites that are ROS biomarkers and mitigators in preovulatory follicular fluid following longer intervals of proestrus likely represents increased follicle progression toward normal intrafollicular events that the luteinizing hormone surge stimulates to promote ovulation of a developmentally competent oocyte.