Effect of L-carnitine on buffalo in vitro embryo development

The aim of this work was to evaluate whether L-carnitine supplementation during IVC improves blastocyst development and cryotolerance of in vitro produced (IVP) buffalo embryos. Abattoir-derived cumulus-oocytes complexes (n=410, over 5 replicates) were matured and fertilized in vitro according to standard procedures (Gasparrini B et al. 2006 Theriogenology 65 (2), 275-287). On day 1 (Day 0 = IVF), zygotes were cultured in SOF supplemented with 8 mg/ml BSA, in the absence (control, n=165) or presence of L-carnitine (n=170) at a concentration (0.25 Mm) selected after a preliminary dose response trial. In vitro culture was carried out at 38.5°C under 5% CO2, 7% O2, and 88% N2. Cleavage and blastocyst rates (in relation to the cleaved embryos) were evaluated on Day 5 and 7, respectively. The blastocysts were vitrified by cryotop in 16.5% ethylene glycol, 16.5% DMSO and 0.5M sucrose and the survival rate, based on morphological criteria, was assessed after 24 h culture. Data were analyzed by Chi square test. Cleavage (81.3% vs 82.1%, in the control and carnitine groups) and blastocyst production (40.0% vs 47.6%, in the control and carnitine groups) were not affected by the treatment. The percentages of fast developing embryos (expanded and hatched blastocysts), i.e. those of better quality, were 17.0 and 23.5%, respectively. Interestingly, the embryos cultured with L-carnitine showed higher survival rates after 24 h culture (78.7% and 96.4%, in the control and carnitine groups, respectively; P<0.01). These results demonstrated that L-carnitine supplementation of culture medium improves the resistance to cryopreservation of IVP buffalo embryos, without affecting blastocyst production. We speculate that the increased cryotolerance in the presence of L-carnitine may be attributed to a better utilization of the endogenous lipid stores, leading to improved embryo quality.