The effects of low levels of PMSG and flush feeding upon embryonic survival in gilts

This experiment was designed to measure the effects of a dose of PMSG (600 IU) or a five-day flush feeding, singly or in combination, on ovulation rate, early embryonic survival, litter size at term and plasma hormone levels during early gestation in 64 Duroc gilts. They were assigned to four treatments, with half of each treatment killed on day 25 of pregnancy and the other half continuing to term.Although treatment with 600 IU of PMSG increased the number of ovulations compared to the controls (P < .05), it failed to increase the number of viable embryos at day 25 of gestation (P > .05). Flush feeding for five days before breeding yield similar results. Fewer embryos were present at day 25 of gestation in those animals receiving a combination $\text{PMSG}$/flush feeding treatment than in any other treatment group (P < 0.01). At day 25 of gestation, the average prenatal survival rate was 71% for all treatments. At parturition, there were no differences between treatment groups in the average number of pigs born per litter; nor were there any differences present for the average number of pigs weaned per litter at four weeks postpartum. Plasma progesterone levels at the onset of treatment, mating and during early gestation were found to be similar among the four treatment groups. Plasma estradiol-17β levels were also similar among the four groups. Based on this experiment, it would appear that factors other than the mere number of viable eggs shed determines the litter size at parturition in swine.