Purpose To determine the effects of α-tocopherol supplementation to oocyte maturation media and embryo culture media on the yield of ovine embryos. Methods α-tocopherol, at concentrations of 0, 50, 100, 200, 400 and 500 µM was supplemented to ovine oocyte or embryo culture media and cultured at 5% or 20% O 2 levels. Percentages of cleavage, morula and blastocyst, total cell count and comet assay were taken as indicators of developmental competence of embryos. Results 200 µM α-tocopherol in embryo culture medium at 20% O 2 level significantly increased the rates of cleavage (P<0.05), morulae (P<0.05) and blastocyst (P<0.01) formation and blastocyst total cell number (P<0.01) when compared with control. The rates of blastocyst formation were also significantly higher in 100 µM (P<0.01) and 400 µM (P<0.05) supplemented groups than control. Conclusion α-tocopherol supplementation may enhance the in vitro developmental competence of ovine embryos by protecting them from oxidative damage.

Vitamin A (all-trans retinol) is an important antioxidant whose role in embryo development in vitro and in vivo is well established. Oxidative stress is a major cause of defective embryo development. This study evaluated the effects of all-trans retinol supplementation to maturation and embryo culture media under different gaseous environments on the development of ovine oocytes and embryos in vitro. The percentages of cleavage, morula and blastocyst, total cell count and comet assay were taken as indicators of developmental competence of embryos. In experiments I and II, all-trans retinol at concentrations of 0, 2, 4, 6, 8 and 10 mM were supplemented to the oocyte maturation medium and cultured in an environment of 5% or 20% O 2 respectively. All-trans retinol supplementation (6 mM) to the maturation medium at 5% O 2 levels significantly increased blastocyst yield and total cell number (P , 0.05). Maturation of oocytes in a 20% O 2 environment bettered cleavage rates in the 6 mM supplemented group compared with the control group (P , 0.05). In experiments III and IV, all-trans retinol, at the aforesaid concentrations was supplemented to embryo culture media under a 5% or 20% O 2 environment, respectively. All-trans retinol supplementation to the embryo culture medium at 5% O 2 levels did not yield any significant result whereas the culture at 20% O 2 levels gave significantly higher blastocyst yield in the 6 mM supplemented group compared with the control group (P , 0.01).Keywords: vitamin A, ovine, in vitro fertilisation, oxidative stress, embryo culture ImplicationsThe supplementation of a suitable quantity of all-trans retinol to oocyte maturation medium or embryo culture medium followed by culture under appropriate gaseous environments protects oocytes and embryos from oxidative damage, thereby greatly enhancing the yields of viable embryos. This could be applied in Animal Biotechnology to increase lamb crops from high-yielding breeds of farm animals, which are seasonal breeders or which have reproduction problems and also to propagate endangered animal species.