The contribution of endogenous lipids to energy production during oocyte maturation is poorly understood. Current maturation media are based predominantly on carbohydrate requirements of oocytes, despite the potential for ATP production via β-oxidation and high levels of intracellular lipid in oocytes of certain species, including the pig. The aim of this study was to investigate the effect of L-carnitine, a stimulator of lipid metabolism, on porcine oocyte maturation.

Oocytes were matured in modified porcine oocyte medium¹ with or without 12mM L-carnitine and 0, 1.5 or 4mM glucose. In the first experiment, pyruvate and lactate were excluded from the media; in the second experiment, the media contained 0.2mM pyruvate and 2mM lactate. The progression of nuclear maturation was determined at 22 and 44h. Data were analysed by ANOVA and Tukey’s post hoc test. In media containing 1.5mM glucose but lacking pyruvate and lactate, the addition of 12mM L-carnitine led to an increased proportion of oocytes reaching MII after 44h, compared to 1.5mM glucose groups without L-carnitine supplementation (36% vs 10%; P<0.05). This difference was not observed after maturation with pyruvate and lactate, where groups lacking glucose had lower MII rates at 44h compared with groups containing glucose, regardless of L-carnitine addition (63% vs 91%; P<0.05). Oocytes matured with pyruvate, lactate and 1.5 or 4mM glucose, with or without 12mM L-carnitine, were then subjected to IVF using frozen-thawed boar sperm and cultured in vitro for 7 days. There was no effect of L-carnitine on oocyte developmental potential.

In conclusion, L-carnitine addition enhanced nuclear maturation in the presence of low glucose concentration when pyruvate and lactate were absent from media, suggesting that lipid metabolism may compensate for certain carbohydrate deficiencies in media. Further research is required to better understand the role lipid metabolism plays in energy generation during oocyte maturation.