E-Poster Presentation ESA-SRB-ANZBMS 2021

A comparison of the fatty acid composition of equine follicular fluid from different sized preovulatory follicles. (#542)

Edwina F Lawson 1 , Manohar Garg 1 , Christopher G Grupen 1 , Mark A Baker 1 , R. John Aitken 1 , Aleona Swegen 1 , Zamira Gibb 1
  1. The University of Newcastle, Callaghan, NSW, Australia

An IVF protocol has not been established in the horse, potentially due to inefficient oocyte maturation and sperm capacitation methods. During in-vivo oocyte maturation, follicular fluid (FF) envelops the oocyte serving as a molecular reservoir of metabolic activity. Fatty acids (FAs) found in FF are incorporated by the oocyte influencing maturation and quality. During ovulation some FF bathes the oviductal epithelium, and if present spermatozoa. To better understand the oocyte maturation milieu and sperm capacitation, the FA composition of FF from preovulatory follicles of increasing diameters were examined.

FF was aspirated from slaughterhouse-derived ovaries of healthy, cycling mares, and follicle diameter was measured using vernier-callipers. FF was aspirated using a 22-gauge needle, centrifuged and stored at −80°C. FA profiles were analysed via direct transesterification, followed by gas chromatography (GC), on a Shimadzu GC2010, using a fused-silica capillary column. 

Individual FA concentrations were reported as percentage, with 14 FAs identified. Palmitic (mean±SD: 30.58±2.44), stearic (26.19±2.15), oleic (15.19±2.54) and linoleic acids (16.02±1.96) had consistently high concentration and small variation across all follicles.  Follicles (n=11) ranged from 9.1mm-50mm and were divided into groups according to diameter: small (n=5, <18mm) and large (n=6, >18mm). Only arachidonic acid (AA) levels were significantly higher in large follicles (mean±SEM: 3.69±0.39) compared to small (1.82±0.61), t-test=2.70, p=0.02.

AA-derived metabolites, especially prostaglandins, influence granulosa-cells steroidogenesis and follicle rupture mechanisms, acting as cell-signalling intermediates in cAMP activation and PI3K/AKT. As such, they may contribute to oocyte maturation and the granulosa gap-junctions breakdown preceding ovulation. Saturated FAs have detrimental effects on oocyte maturation, two of which (palmitic/stearic) where in high concentrations across all follicles. Except for the polyunsaturated AA, these results indicate equine preovulatory follicles contain high steady-state FA concentrations, regardless of size. Research is required to further examine the role of equine FAs during oocyte maturation and sperm capacitation. 

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