Stage of Gestation when Uterine Capacity Limits Embryo Survival in Gilts

Three trials were conducted to define the stage of gestation at which uterine capacity acts to reduce 25-day litter size of gilts. This was done by superinduction, i.e., increasing the number of potential embryos by transferring additional embryos to the uterus of a pregnant recipient. It was assumed that superinduction would significantly increase litter size if it was performed after the stage of gestation in which mechanisms that control uterine capacity are operative. In two out of three trials, superinduction on Day 7 (onset of estrus Day 0) did not significantly increase 25-day litter size. This indicates that mechanisms which control uterine capacity are operating after Day 7 to reduce litter size to a level characteristic of the gilt uterus. A summary of Day 7 superinduction treatments in all trials demonstrates that 14.9 total embryos and 12.3 live embryos represent the average levels of uterine capacity characteristic of gilts sampled in this experiment.