The Effects of Fetal Number on Maternal Serum Progesterone and Estradiol of Ewes During Pregnancy

Abstract

Twenty nine ewes with similar weight and age were used to study the contributions
of fetal number to circulating concentrations of progesterone or estradiol during whole pregnancy. The ewes were injected with 1 ml synthetic prostaglandin PGF2a (Prosolvin, Intervet) i.m. and were repeated on d 11 from the first injection to
synchronize the estrous cycle. Based on the number of lambs born at parturition date, the ewes were assigned into 5 groups (0, 1, 2, 3, and 4) with n = 3, 12, 9, 4, and 1, respectively. Blood samples were collected every other week for progesterone and estradiol analyses using radioiinmuiioassay. Simple correlation was used to determine the relationship between the fetal number and serum progesterone or estradiol concentrations. The results of the experiment showed that fetal number correlated with the maternal scrum progesterone concentrations either during the first half of pregnancy (P<0.01) with r = 0.70, the second half of pregnancy (P<0.01) with r = 0.75, or during the whole period of pregnancy (P<0.01) with r = 0,7 7. Fetal number did not correlate with maternal sennn concentrations of estradiol during the first half pregnancy. However, fetal number correlated with the estradiol concentrations during the second half of pregnancy (P<0.01) with r = 0.49 and during the whole period of pregnancy (P<0.05) with r = 0,46. It was concluded that fetal number strongly affected maternal serum concentrations of progesterone, and to a lesser extend those of estradiol, during pregnancy.