Influence of pig embryos on uterine growth.

The influence of embryos on growth of the uterus was determined by comparing uterine length, weight and diameter between gravid and nongravid horns within unilaterally pregnant gilts. Eighty-two prepubertal gilts were ovariectomized unilaterally at 5 mo of age, and the ipsilateral uterine horn was ligated near the junction of the uterine horns. Gilts were mated and were assigned randomly for examination on either d 9, 12, 15, 18, 21, 24 or 27 of gestation. Absolute differences and ratios in length, weight and diameter between gravid and nongravid horns of unilaterally pregnant gilts were analyzed. The gravid horn was 40% longer than the nongravid horn from d 18 to 27. Uterine horns with embryos increased linearly in weight and diameter (P less than .01) between d 15 and 27. Embryos, or the signals that they might give, apparently caused increases in length, weight and diameter of the uterine horn by d 18, but not before.