Effect of Stage of Gestation and Uterine Space on Prenatal Survival in the Pig

The influence of uterine space on prenatal survival was examined in 251 gilts at three stages of gestation: days 25 to 30, days 31 to 40 and days 41 to term. Uterine space was varied so that either twice normal, half normal or the normal amount of uterine space was available per embryo. When the uterus was unchanged but the number of embryos entering the uterus was reduced the proportion of embryos surviving at any stage of gestation was not different from normal. Decreasing the uterine space to half that of normal did not affect embryo survival to day 30 but the proportion of embryos surviving after day 30 was reduced. These results demonstrate that uterine space is not associated with the embryonic mortality normally observed before day 30 but after day 30 it may be a factor in fetal death when large numbers of fetuses are present or when uterine space is restricted.