Adelaide, Adelaide, South Australia, Australia.
The role of the thyroid hormones thyroxine (T4) and triidothyronine (T3) in vitro embryo production has not been widely studied. In cattle the addition of T4 plus T3 to in vitro oocyte maturation media has been shown not to influence blastocyst rate or cell number (1). However it was suggested that these hormones may have beneficial effects in species where in vitro maturation is extended such as the pig and human. The aim of the present study therefore was to determine whether the addition of T4 and/or T3 to defined porcine in vitro maturation media could increase in vitro embryo production. Porcine ovaries were obtained from a local abattoir and small antral follicles 3-6mm in diameter were aspirated in the laboratory. Cumulus –oocyte complexes were matured in BOMED maturation media plus PVA containing 0, 25, 50 or 100ng/ml of T4 plus T3 in experiment one or 0, 25, 40 or 100ng/ml of T3 in experiment two for 44 hours. Following maturation COCs were coincubated with 5 x 105 sperm /ml of mixed boar semen for 6 hours. After fertilisation the cumulus cells were removed and the zygotes cultured in PZM-5. The number of oocytes that developed to blastocyst stage on day 5 and 6 stage and differentially stained to determine day 6 blastocyst cell number. In the first experiment one the addition of 50 ng/ml of T4 and T3 increased day 6 blastocyst inner cell mass number compared with control ( P<0.05; 7.0 vs 4.0 respectively ). In experiment two the addition of 50 ng/ul of T3 increased day 5 blastocyst rate (P<0.5; 46 vs 36.5% respectively). In conclusion our results suggest that the addition of T4 and /or T3 to defined porcine maturation media have beneficial effects for in vitro embryo production.