Impact of Equine and Bovine Oocyte Maturation in Follicular Fluid From Young and Old Mares on Embryo Production in Vitro

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Equine follicular fluid (FF) provides autocrine and paracrine factors from theca, granulosa, and cumulus cells, both reflecting and impacting oocyte and follicle maturation. We hypothesized that maturation of oocytes in FF from old versus young mares has a deleterious effect on oocyte maturation and their subsequent developmental potential. Follicular fluid was collected from the large, dominant follicle from young mares (4–13 years) or old mares (21–26 years) and classified as: (1) Noninduced follicular fluid (NFF), FF from noninduced follicle 33 ± 3 mm, or (2) Induced follicular fluid (IFF), FF collected ˜24 hours after administration of ovulation-inducing drugs when a follicle 33 ± 3 mm was observed. In experiment 1, immature equine oocytes were collected, matured in vitro for 30 ± 2 hours in 100% IFF, collected from young or old mares, with the addition of follicle stimulating hormone (5 mU/mL), then fertilized by intracytoplasmic sperm injection. In experiment 2, immature bovine oocytes were collected, matured in 100% IFF or NFF, collected from young mares or old mares, then fertilized via in vitro fertilization. In experiment 1, more blastocysts tended (P = .08) to be produced from equine oocytes that were matured in old versus young mare FF. In experiment 2, when IFF and NFF groups were combined, cleavage rates were higher (P = .001) when bovine oocytes were matured in FF from young than old mares. In contrast to our hypothesis, we observed no conclusive evidence that FF from old mares has a deleterious impact on oocytes and their early developmental potential.HighlightsThe effect of equine and bovine oocyte maturation in follicular fluid (FF) collected from large, dominant follicles of young and old mares was compared.Follicular fluid from the follicles of old mares tended to increase blastocyst development after maturation of equine or bovine oocytes.With no exogenous hormone additions, FF from young when compared to old mares’ follicles significantly increased cleavage rates of bovine oocytes after IVF.With no exogenous hormone additions and when compared for FF from follicles without maturation induction, FF from young versus old mares significantly increased cleavage rates of bovine oocytes after IVF.In these experiments, we did observe effects of mare age on FF used for oocyte maturation; however, the results were mixed, with young mare FF having a positive effect on cleavage rates and old mare FF tending to increase blastocyst development.

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