The Effect of Reducing the Number of Embryos During Early Stages of Gestation on the Maintenance of Pregnancy in the Pig

The number of embryos has been experimentally reduced during early stages of gestation in the pig by means of partial hysterectomy (du Mesnil du Buisson & Rombauts, 1963). Pregnancy is maintained in animals in which only one embryo remains so long as all the uterus is removed except that portion occupied by the embryo. By contrast, if the embryos are confined to one of the uterine horns, the unilateral pregnancy so established is not maintained unless the non-pregnant horn is removed before the 14th day of the oestrous cycle (du Mesnil du Buisson, 1961). The absence of embryos in one horn leads to regression of corpora lutea and thus complete failure of pregnancy at an early stage. These observations suggest that the presence of embryos in a large part of both uterine