Submitted to: Biology of Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 2, 2003
Publication Date: January 1, 2004
Citation: VALLET, J.L., CHRISTENSON, R.K. EFFECT OF PROGESTERONE, MIFEPRISTONE, AND ESTROGEN TREATMENT DURING EARLY PREGNANCY ON CONCEPTUS DEVELOPMENT AND UTERINE CAPACITY IN SWINE. BIOLOGY OF REPRODUCTION. 2004. V. 70(1). p. 92-98. Interpretive Summary: With today's technology, litter size in swine is limited by an empirically measured trait called uterine capacity, which is defined as the number of fetuses that can be supported by the pig uterus until farrowing. Although the timing of both uterine function and conceptus development have been shown to be influenced by the presence of progesterone during early pregnancy, the effect of manipulation of progesterone during early pregnancy on uterine capacity has never been explored. We performed a series of experiments to investigate the effect of increasing or decreasing (using the progesterone antagonist RU486) progesterone on day 2 and 3 of pregnancy on uterine capacity. Results indicated that (1) increased progesterone on day 2 and 3 of pregnancy decreased uterine capacity, which was associated with increased fetal weights; and (2) decreased progesterone (using RU486) inhibited uterine protein secretion, conceptus development and later uterine capacity, seemingly by elimination of a subset of below average weight fetuses. This suggests that both too much and too little progesterone during early pregnancy has a negative impact on uterine capacity, and that an optimal progesterone during this period likely exists that maximizes uterine capacity. The definition of the optimal progesterone could be useful in improving uterine capacity and litter size in swine.
Technical Abstract: A series of experiments to investigate the influence of progesterone on day 2 and 3 of pregnancy on conceptus development and uterine capacity was performed. In experiment 1, unilaterally hysterectomized- ovariectomized (UHO) white crossbred gilts were given either no treatment, estradiol valerate (5 mg given on Day 11 and 12) or progesterone treatment (200 mg/day on Days 2 and 3 after mating). On Day 105 of pregnancy, each fetus and its associated placenta were weighed and the number of live and dead fetuses was recorded for each litter. Early progesterone treatment decreased the number of small fetuses, thereby reducing (P < 0.05) litter size (a measure of uterine capacity in UHO gilts). In experiment 2, intact white crossbred gilts were mated, treated with no treatment or progesterone treatment on Days 2 and 3 of pregnancy, and farrowed. Progesterone-treatment decreased (P < 0.05) pregnancy rates. In pregnant gilts, progesterone had no effect on the number of live or stillborn piglets at birth, and gestation length was decreased (P < 0.05). Progesterone treatment did not affect the number of large or small piglets. In experiment 3, intact gilts were mated at estrus and then received either 1) no treatment, 2) 100 mg, 3) 200 mg, or 4) 400 mg mifepristone (RU486) on Day 2 of pregnancy. On Day 11 of pregnancy, both uterine horns were flushed, the number and diameter of each conceptus was recorded and the flushings were measured for total protein and acid phosphatase. The 400 mg mifepristone treatment significantly decreased conceptus diameter (P < 0.05) and total protein in the uterine flushings (P = 0.06). In experiment 4, UHO gilts were mated at estrus, injected with either corn oil (control) or mifepristone (400 mg) on Day 2 of pregnancy, slaughtered on Day 105 of pregnancy, and the number and weight of live fetuses and placentas was recorded. Similar to the effect of progesterone treatment, mifepristone decreased uterine capacity by decreasing the number of small conceptuses. These data suggest that progesterone concentrations on Days 2 and 3 of pregnancy influence the rate of conceptus development during early pregnancy and uterine capacity during later pregnancy.