Fatty acid composition of lipids in immature cattle, pig and sheep oocyteswith intact zona pellucida

Cattle, pig and sheep oocytes isolated from healthy cumulus-oocyte complexe s were pooled, within species, to provide samples of immature denuded oocyt es with intact zona pellucida (n = 1000 per sample) for determination of fa tty acid mass and composition in total Lipid, constituent phospholipid and triglyceride. Acyl-containing lipid extracts, transmethylated in the presen ce of a reference penta-decaenoic acid (15:0), yielded fatty acid methyl es ters which were analysed by gas chromatography Mean (+/- SEM) fatty acid co ntent in samples of pig oocytes (161 +/- 18 mu g per 1000 oocytes) was grea ter than that in cattle (63 +/- 6 mu g; P < 0.01) and sheep oocytes (89 +/- 7 mu g; P < 0.05). Of 24 fatty acids detected, palmitic (16:0; 25-35%, w/w ), stearic (18:0; 14-16%) and oleic (18:1n-9; 22-26%) acids were most promi nent in all three species. Saturated fatty acids (mean = 45-55%, w/w) were more abundant than mono- (27-34%) or polyunsaturates (11-21%). Fatty acids of the n-6 series, notably linoleic (18:2n-6; 5-8%, w/w) and arachidonic ac id (20:4n-6; 1-3%), were the most abundant polyunsaturates. Phospholipid co nsistently accounted for a quarter of all fatty acids in the three species, but ruminant oocytes had a lower complement of polyunsaturates (14-19%, w/ w) in this fraction than pig oocytes (34%, w/w) which, for example, had a t hree- to fourfold greater linoleic acid content. An estimated 74 ng of fatt y acid was sequestered in the triglyceride fraction of individual pig oocyt es compared with 23-25 ng in ruminant oocytes (P < 0.01). It is concluded t hat the greater fatty acid content of pig oocytes is primarily due to more abundant triglyceride reserves. Furthermore, this species-specific differen ce, and that in respect of polyunsaturated fatty acid reserves, may underli e the contrasting chilling, culture and cryopreservation sensitivities of e mbryos derived from pig and ruminant (cattle, sheep) oocytes.