Reproductive Performance after Unilateral or Bilateral Oviduct Transfer of 2-Cell Embryos in Mice

Embryo transfer (ET) is a frequent procedure in contemporary animal and transgenic facilities. We compared the reproductive performance of mice after unilateral and bilateral ET of 15 to 18 two-cell embryos per recipient. The genetic backgrounds of the donors were C57BL/6J (B6J), C57BL/6N (B6N), or fewer than 5 generations of backcrossing to B6 (unknown substrain, <5G B6). The pregnancy rate was significantly higher for bilateral than for unilateral ET for B6J lines (85.4% compared with 79%) but similar between modes for B6N (73.7% compared with 77.9%) and <5G B6 (77% compared with 74.5%) lines. The birth rates after unilateral and bilateral ET were 30.8% and 33.0% for B6J lines, 24.5% and 26.9% for B6N lines, and 31.0% compared with 28.2% for