Plasma oestrone and oestradiol concentrations throughout gestation in cattle: relationship to stage of gestation and fetal number

The objectives of the study were to characterise the peripheral plasma oest rone (E1) and oestradiol-17 beta (E2) concentrations throughout gestation i n the cow and to correlate this with the stage of gestation and fetal numbe r. Cows (n = 10) were equally divided into two groups after non-surgical em bryo transfer of in-vitro matured and in-vitro fertilised (IVM-IVF) embryos ; Group 1 received a single embryo, Group 2 received twin embryos. Blood wa s collected about every third day from day 0 (day 0 was defined as first da y of standing oestrus), then daily for the last 10 days of gestation and sa mpling was stopped one day post partum. Plasma E1 concentration exceeded th at of E2 throughout gestation in both groups of cows. The time trend concen trations of plasma E1 were significantly affected by the stage of gestation (P < 0.01) and fetal number (P < 0.01) in the last two trimesters of gesta tion. The time trend concentrations of plasma E2 were significantly affecte d by the stage of gestation (P < 0.01) but not foetal number (P = 0.09). In both groups there was marked preparturient increase in E1 and E2 concentra tions. Plasma E2 profile between days 10 prepartum to parturition parallele d E1 in cows carrying a single foetus but was disparate during the same per iod in the twin-bearing cows. To conclude, our results indicate that although plasma E1 concentration was greater than E2 throughout gestation, both were related to the stage of ge station and that fetal number was correlated with circulating E1 levels in the last two trimesters of gestation.