Uterine Capacity at two Stages of Gestation in Gilts following Embryo Superinduction

Of a total of 88 Duroc and Yorkshire gilts, 44 served as controls (A), additional embryos were added (superinduction) to uteri of 28 (B) and 16 non-mated recipients received developing embryos from donor females (C). Embryos were transferred at the two- or four-cell stage. In an attempt to determine when in the developmental process the number of embryos undergoing development becomes limited, some gilts were slaughtered at 25 (22 to 28) days and the others at 105 (102 to 108) days of gestation. Gilts slaughtered at 25 days in treatments A, B and C had conception rates of 24/26, 11/16 and 6/10, an average of 13.0, 23.9 and 11.0 potential embryos and 9.6, 12.0 and 6.0 normal embryos, respectively. At 105 days gestation gilts on the same respective treatments had conception rates of 14/18, 9/12 and 1/6, an average of 12.9, 23.6 and 9.0 potential embryos and 9.6, 9.8 and 7.0 normal fetuses. Doubling the number of potential embryos did not significantly change litter size at either 25 or 105 days gestation. The data indicate that the primary mechanism responsible for establishing uterine capacity is operative prior to day 25 of gestation.