Early embryonic survival in the pig: Can it be improved?

A major limitation for increasing litter size in swine is embryonic loss that occurs during the 2nd to 3rd wk of gestation. High ovulation rates of modern sows have more than supplied the potential number of embryos necessary to improve litter size. The current challenge is determining how early conceptus development affects the ability to maintain the viability through the remaining 90 d of gestation to maximize farrowing house production. To achieve this, it is necessary to identify and understand the possible causes of embryonic death. Because fertilization rates are generally high in swine, early embryonic loss during the first 20 d of gestation is considered to critically effect potential litter size. There are three periods during which early embryonic loss can occur: 1) pre-elongation development, 2) trophoblastic elongation, and 3) placental attachment. The first two periods are related to time of fertilization and subsequent developmental rate for each individual embryo within the litter. Asynchrony in embryonic development relative to uterine develop