Canadian Health&Care; Mall

The previously demonstrated effects of manipulation of progesterone and estrogen during pregnancy on the rate of conceptus development, combined with the hypothesis that the Meishan accomplishes greater fertility by reducing the rate of conceptus development, suggested to us that manipulation of progesterone or estrogen during early pregnancy might influence uterine capacity and litter size. Although the effect of early progesterone on pregnancy success has been studied previously, no experiments on the influence of early progesterone specifically on uterine capacity have been performed. The unilateral hysterectomized-ovariecto-mized (UHO) surgical model was developed specifically for this purpose. In this model, the number of viable embryos available typically exceeds the capacity of the remaining uterine horn, providing a measure of uterine capacity that is independent of ovulation rate, fertilization rate, and embryonic mortality. Thus, the objective of the first experiment was to test the effect of estrogen treatment and early progesterone treatment on uterine capacity in UHO gilts. The objective of the second experiment was to determine in intact gilts whether the accelerating effects of early progesterone treatment were still present at farrowing and whether progesterone influenced stillbirth rate or preweaning survival. The objective of the third experiment was to determine whether interference with progesterone using mifepristone would have effects in intact gilts opposite to those observed by Vallet et al.. Experiment four tested the effect of decelerating conceptus development with mifepristone on uterine capacity using UHO gilts. Thus, the primary objectives of the following experiments were to test the effect of progesterone, mifepristone, or estrogen treatment on conceptus development, uterine capacity, and litter size in European breed gilts.