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Experiment 2 Intact white crossbred gilts were observed once daily for estrous behavior beginning at 200 days of age and then were mated at standing estrus by artificial insemination using semen collected from mature white crossbred boars. Gilts were randomly allocated to receive either no treatment (control) or 200 mg/day of progesterone on Days 2 and 3 of pregnancy. Gilts were farrowed, and gestation length was recorded for each gilt. At birth, the numbers of live and stillborn piglets born to each gilt were recorded, and each piglet was weighed. Piglets were weighed again at weaning (approximately 21 days of age) and at approximately 56 days of age. Experiment 3 Intact white crossbred gilts were checked once daily for estrous behavior and were mated by artificial insemination at standing estrus after at least one estrous cycle of normal length. Gilts were assigned at random to receive 1) no treatment or treatment with 2) 100 mg, 3) 200 mg, or 4) 400 mg mifepristone in corn oil on Day 2 of pregnancy (Day 0 = day of estrus). On Day 11, gilts were laparotomized, and each uterine horn was flushed with 20 ml sterile 0.9% saline. Pregnancy of each gilt was confirmed by the presence of conceptuses, and the number and diameter of conceptuses recovered were recorded for each gilt. Uterine flushings were evaluated for total protein and total acid phosphatase.