MATERNAL PLASMA ESTRONE SULFATE PROFILE DURING PREGNANCY IN THE COW -COMPARISON BETWEEN SINGLETON AND TWIN PREGNANCIES

Peripheral plasma estrone sulfate (E-1-S) concentrations were characte rized throughout gestation in singleton and twin bearing cows by a dir ect radioimmunoassay method. Maternal plasma E-1 S was detectable from around day 100 and after that its concentration increased progressive ly to term in both singleton (n=5) and twin bearing (n=5) cows. Twin b earing cows had a significantly higher E-1-S concentrations in some ti me from mid-gestation to term when compared to singleton cows. E-1-S c oncentration in the twin bearing cows increased rapidly in the third t rimester and peaked (16.7 ng/ml) on the day of calving. In the singlet on cows the concentration increased gradually and peaked (7.1 ng/ml) a bout 10 days before calving and then subsequently decreased. Our resul ts indicate that singleton and twin bearing cows show a disparate E-1- S profile from mid-gestation to term.