Category Archives: Progesterone

Experiment 1 Pregnancy rate was 65% for gilts in this experiment and did not differ among treatments (Table 1). No significant differences were observed between control and estradiol valerate-treated gilts for any of the other traits measured in this experiment. The number of live conceptuses was decreased (P = 0.05) for progesterone-treated gilts compared with control gilts. Although the number of dead fetuses was numerically greater in the progesterone-treated gilts, the effect of progesterone treatment on the number of dead fetuses (mummies) was not significant. Placental weights and fetal hematocrits did not differ between progesterone-treated and control gilts. (more…)

In experiment 4, pregnancy rates between treatment groups were analyzed using x2. Number of CL, litter size, average fetal hematocrit, average fetal weight, average brain weight, average heart weight, average liver weight, and average placental weight (each trait averaged within litter) were analyzed using ANOVA with a model that included the effect of treatment. Average brain weight, heart weight, and liver weight were also subjected to ANOVA using average fetal weight as a covariate and a model that included the effect of treatment. (more…)

Gestation length and litter size at birth were also used as covariates in the analysis of birth weights. For weaning and Day-56 weights, the true age of each litter when measurements were recorded was used as a covariate. In addition, the numbers of piglets weighing more than (large) and less than (small) the mean piglet birth weight for the control gilts were determined for each litter, and the effect of treatment on the number of large and small piglets per litter was analyzed by ANOVA. (more…)

For fetal weights, average placental weight for that gilt was used as a covariate in the analysis. To assess whether treatment effects on uterine capacity were uniformly distributed among conceptuses of different weights, the number of fetuses weighing more than (large) and less than (small) the mean fetal weight of the control group and the number of placentas weighing more than (large) and less than (small) the mean placental weight of the control group were determined for each gilt. (more…)

Experiment 4 White crossbred gilts were unilaterally hysterectomized-ovariecto-mized at approximately 160 days of age, observed once daily for estrous behavior beginning about 200 days of age, and mated by artificial insemination at standing estrus after at least one estrous cycle of normal length. On Day 2 of pregnancy, gilts were assigned at random to receive either 1) corn oil (10 ml) or 2) 400 mg mifepristone in corn oil i.m. At 105 days of gestation, gilts were killed, and the reproductive tract of each gilt was recovered and opened. A blood sample for measurement of hematocrit was collected from each live fetus. The number of live and dead fetuses and the weight of each live fetus were recorded. Brain, heart, and liver weights for each fetus were also recorded. The placenta for each fetus was dissected from the endometrium and weighed. (more…)

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. (more…)

All experiments were performed according to Federation of Animal Science Society guidelines for the use of agricultural animals in research, and each experiment was reviewed and approved by the MARC Institutional Animal Care and Use Committee. Experiment 1 Intact white crossbred gilts were unilaterally hysterectomized-ovari-ectomized at approximately 160 days of age. At 200 days of age, these gilts were observed once daily for estrous behavior and were mated after at least one estrous cycle of normal length (17-23 days) using artificial insemination with semen collected from mature white crossbred boars. (more…)

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. (more…)

The slower rate of conceptus development in Meishan gilts has been suggested to be due in part to decreased conceptus estrogen secretion in this breed. However, others have suggested that both the decreased estrogen secretion and the slower growth rate are a consequence of the decreased uterine protein secretion of the Meishan. In support of the hypothesis that the rate of conceptus development in the Meishan is due to conceptus estrogen secretion, estrogen treatment of Meishan gilts on Days 12 and 13 of pregnancy significantly increased placental weights. This increase in placental weights was not associated with a decrease in litter size. However, the number of observations in this experiment may have precluded obtaining a significant association between the two traits. It remains uncertain what effect estrogen treatment might have on placental weights and uterine capacity in European breed gilts. (more…)

In the Meishan swine breed, which has greater fertility than European breeds, uterine protein secretion and conceptus development and conceptus estrogen secretion during early pregnancy are reduced compared with European breeds. One hypothesis is that this slower conceptus development during early pregnancy results in smaller placentas during later pregnancy and allows the uterus to accommodate more fetuses, thus increasing uterine capacity, which is defined as the number of live fetuses that can be maintained by the uterus during gestation. (more…)