Effect of knockout serum replacement supplementation to culture medium on porcine blastocyst development and piglet production

We have previously developed chemically defined media suitable for in vitro production (IVP) of porcine embryos and subsequently generated piglets by nonsurgical embryo transfer. In this study, to further improve the culture conditions for IVP of porcine embryos, we evaluated the effect of knockout serum replacement (KSR), a substitute for serum or albumin, on the viability and development of porcine blastocysts. The addition of 5% (v:v) KSR to porcine blastocyst medium (PBM) on Day 5 (Day 0 = IVF) significantly increased the survival and hatching rates of blastocysts and the total cell number of Day-7 blastocysts compared with those in cultures without KSR or addition of 10% fetal bovine serum. Furthermore, the number of cells in the trophectoderm of Day-6 blastocysts and the ATP content of Day-7 blastocysts cultured with 5% KSR were significantly higher than those of blastocysts cultured without KSR. The mRNA expression of a rate-limiting enzyme in β-oxidation, carnitine palmitoyltransferase 1, in Day-6 blastocysts, and a serine proteinase, urokinase-type plasminogen activator, in Day-7 blastocysts cultured in 5% KSR-PBM was significantly higher than that of blastocysts cultured in PBM alone. Four of eight recipients (50%), in which Day-5 blastocysts treated with 5% KSR were transferred nonsurgically, became pregnant. However, the efficiency of piglet production (percentage of piglets born based on the number of embryos transferred) was similar to recipients with transferred blastocysts treated without KSR. The present study demonstrated that the addition of KSR to PBM enhanced the in vitro viability of porcine blastocysts. In addition, our data suggest that KSR improved development to the hatching stage and blastocyst quality by increasing ATP content and hatching-related mRNA expression of blastocysts.