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 <5G B6 lines, with no significant difference between the modes of ET. Birth rate was significantly higher for B6J lines than B6N lines after both unilateral and bilateral ET. For B6J and B6N lines, the number of pups born per litter was significantly higher for bilateral than unilateral ET. Unilateral ET yielded 0.24 to 0.31 pup per embryo transferred compared with 0.27 to 0.33 pups after bilateral ET. Over all genetic backgrounds, 3.03 to 4.09 embryos were required to produce a single pup. The present study provides data to aid in decision-making as to whether unilateral or bilateral ET should be performed. Bilateral ET results in a larger litter but increases pain and discomfort in recipients. However, unilateral ET saves time and contributes to refinement because surgical trauma is reduced.

Productivity of superovulated C57BL/6J oocyte donors at different ages.

Superovulation is often used to increase the number of oocytes that can be collected from donor females for in vitro fertilization. Donor age can affect the quantity and quality of oocytes produced during superovulation, and in some strains of mice juvenile females are optimal donors. The authors reviewed donor and oocyte records from a breeding program to evaluate how donor age affects the number and fertilization efficiency of oocytes collected from C57BL/6J mice. Generally fewer oocytes per donor were collected from females aged > 32 d than from females aged 21-32 d. Fertilization efficiency of oocytes generally declined with donor age when oocytes were fertilized with fresh or with stored sperm. These findings suggest that the use of younger C57BL/6J donors, instead of older donors, can reduce the number of donors needed for IVF procedures.