Category Archives: Progesterone

These mechanisms appear to fail below a fetal weight of 800 g. Although numerous other factors also contribute to the loss of small piglets, improper brain development that occurs in these small fetuses may contribute to perinatal and neonatal losses. These data indicate that early progesterone treatment decreased uterine capacity at 105 days of gestation in UHO gilts, possibly by accelerating fetal growth. Early progesterone treatment had limited effects on litter size and birth weights in intact white crossbred gilts. Mifepristone treatment on Day 2 of gestation decreased both conceptus diameter and uterine protein secretion measured on Day 11. (more…)

However, experiments in which the alleviation of nutritional effects by progesterone treatment was attempted have resulted in equivocal results. The current results could suggest the hypothesis that giving exogenous progesterone to compensate for the effect of nutrition is extremely difficult because it would result in many cases in either too much progesterone or inappropriate timing of progesterone influence and would therefore also result in decreased uterine capacity and litter size. (more…)

Both progesterone and mifepristone treatment increased average fetal weights. However, progesterone treatment did not affect the number of large or small fetuses or placentas. In contrast, mifepristone specifically reduced the number of small fetuses and placentas but had no effect on the number of large fetuses or placentas. These results suggest that progesterone likely acted by accelerating fetal growth. The faster growth rate may have increased the risk of loss due to limitations in uterine capacity. Mifepristone treatment, by contrast, may have decreased the survival rate of smaller fetuses in some way, causing them to be underrepresented in the litter and thus decreasing litter size. (more…)

Results of experiment 2 indicated a slight negative effect on overall pregnancy rate. However, for those gilts in which pregnancy was established, progesterone did not affect litter size, arguing against these mechanisms as an explanation for the results of experiment 1. In addition, results of experiment 3 indicate that the number of blastocysts was not reduced by Day 11 in gilts given doses of mifepristone up to 400 mg, suggesting that fertilization rate and oviductal transport were unaffected in mifepristone-treated gilts. Interference by mifepristone with the process of elongation, which occurs after Day 11, is still a possibility. (more…)

Experiment 1, in which exogenous estradiol was administered, failed to demonstrate an increase in placental weights similar to that obtained previously using Meishan gilts. Estrogen levels in the uterus of the Meishan from about Day 11 to Day 13 of gestation are significantly lower than those in the uterus of white crossbred gilts. The amount of estrogen already present in white crossbred gilts on Days 11 and 12 may be sufficient to saturate estrogen receptors, thus explaining the lack of effect of exogenous estrogen. (more…)

The pattern of rise in progesterone during the early es-trous cycle and pregnancy has been examined in numerous experiments. Measurable increases in progesterone concentrations in the peripheral plasma are typically observed by Day 3, and luteal phase levels (15-25 ng/ml) are reached by about Day 6. The dose of progesterone used in the current experiment has also been used in numerous studies to mimic progesterone concentration during the luteal phase. (more…)

Previous studies have demonstrated that both protein secretion and conceptus development are highly variable and change rapidly at this stage of pregnancy (e.g., conceptuses change from spherical to filamentous blastocysts within 24 h). A factor contributing to this variation may be the use of once daily estrous detection in this experiment; the interval from first detection of estrus to ovulation in gilts varies from 23 to 48 h. By chance, the gilts treated with 100 mg mifepristone may have been more advanced than the control gilts, resulting in three of the nine gilts already having filamentous blastocysts by Day 11. (more…)

Results of experiment 3 supported this hypothesis. For gilts treated with the 400mg dose of mifepristone, both conceptus development and uterine protein secretion were lower in the mifepristone-treated gilts compared with controls. Because these results are qualitatively similar to previous results obtained using Meishan gilts, the effect of this treatment on uterine capacity was examined. Unexpectedly, uterine capacity was also decreased in the mifepristone-treated gilts compared with controls. Unlike the effect of early progesterone treatment, mifepristone resulted in fewer small conceptuses (both small fetuses and small placentas) in the mifepristone-treated gilts. (more…)

The first experiment demonstrated the effect of early progesterone treatment on uterine capacity in pigs. Uterine capacity, measured as the number of live fetuses in UHO gilts, was decreased in progesterone-treated gilts compared with control gilts. This decrease occurred in association with increased fetal weights at 105 days of gestation. Further analysis suggested that the increased fetal weight was not due to differences in survival of large or small fetuses in progesterone-treated gilts. Thus, early progesterone treatment may have accelerated fetal development. (more…)

Experiment 3 Results of this experiment are summarized in Table 3. Mifepristone appeared to have a biphasic effect. Conceptus diameter (P = 0.07) and uterine acid phosphatase secretion (P < 0.05) were both increased at the 100-mg dose. By contrast, conceptus diameter (P < 0.05) and total uterine protein secretion (P = 0.06) were decreased at the 400-mg dose. There was no effect of the four treatments on the number of conceptuses recovered on Day 11 of gestation. There was also no effect of the four treatments on variation in conceptus diameter, as measured by the average within-litter CV. (more…)