Dietary intakes of polyunsaturated fatty acids are thought to mediate a wide range of actions in reproductive tissues. This includes the effects on ovarian follicle and corpus luteum functions via improved energy efficiency as well as providing precursors for the synthesis of signalling molecules such as steroids and prostaglandins. An appropriate level of α-linolenic acid (ALA) in the oocyte maturation medium has been shown to induce molecular changes associated with oocyte maturation and embryo developmental competence. In that light, we hypothesised that supplementation of exogenous ALA to maturation media could enhance nuclear maturation and embryonic development in the goat. A preliminary experiment was executed to measure the level of ALA in antral follicles by gas chromatography/mass spectrometry analysis. Our results revealed that the concentration of ALA in follicular fluids ranged from 0.006 to 0.02 mg mL–1 (21.5 to 71.8 µM, with a mean of ~50 µM). To test the effect of ALA on the competence of goat oocytes to complete meiotic maturation to metaphase II and sustain embryonic development, ovaries were obtained from a local abattoir. Cumulus–oocyte complexes were recovered by the slicing method followed by selection of oocytes with a homogenous cytoplasm and at least three layers of compact cumulus cells. The cumulus–oocyte complexes were placed in maturation media supplemented with 50 µM ALA. Oocytes in the control group were incubated in the same maturation medium without ALA. In vitro maturation (IVM) was performed in a humidified atmosphere containing 5% CO2, 5% O2, and 90% N2 at 38.5°C for 24 h. After IVM, several oocytes from the treatment (n = 170) and control (n = 166) groups were stained with Hoechst and were evaluated in relation to their metaphase-II rate. Other groups of oocytes from both the treatment (n = 70) and control (n = 61) groups were subjected to parthenogenetic activation by applying 1 min of exposure to 2.5 µM ionomycin followed by 2 mM 6-DMAP treatment for 3 h. After activation, oocytes were cultured in CR1aa medium for 7 days under the conditions stated above. Four replications were performed. Differences in developmental rates were analysed for significance by one-way ANOVA using SAS version 8.0 (SAS Institute Inc., Cary, NC, USA), considering P < 0.05 to be significant. As a result, supplementation of the maturation media with ALA did not appear to affect cumulus expansion. In contrast, IVM of goat oocytes in the presence of ALA resulted in a significantly higher maturation rate compared with maturation without ALA supplementation (66.4% v. 57.9%). Likewise, addition of ALA to the IVM medium significantly increased the rate of cleavage (60.1% v. 52.4%) and blastocyst formation (22.6% v. 14.9%), calculated from the activated oocytes. Collectively, the results of our study show that supplementation of IVM media with 50 µM ALA promotes nuclear maturation, increases cleavage rate, and results in higher blastocyst rate in goat oocytes after parthenogenetic activation. Thus, providing appropriate levels of ALA in maturation media could have beneficial effects on embryo development and reproductive efficiency in the goat.
The supplementation of ovine oocyte maturation medium with triiodothyronine affects the embryo development and apoptotic gene expression
