Oestrone sulfate commences an increase around 50 days of gestation in bovine peripheral blood

The objective of this study was to determine the peripheral plasma concentr ation of oestrone sulfate during early gestation in the cow with a sensitiv e assay system. Five Holstein heifers were inseminated on oestrus and bled from the jugular vein at regular intervals until 100 days of gestation. Oes trone sulfate, oestrone and oestradiol-17 beta in blood plasma were extract ed with a reverse-phase cartridge and each measured by specific radioimmuno assay. Oestrone sulfate in bovine circulation started to increase around 50 days of gestation. whereas oestrone and oestradiol-17 beta remained at bas al concentrations for 80 days. The plasma concentration of oestrone sulfate increased gradually and linearly from 50 days of gestation, and was drasti cally elevated after 80 days of gestation before the increase in unconjugat ed oestrogens. The rate of increase from 80 to 100 days was the greatest fo r oestrone sulfate concentration among all oestrogens. These results sugges t that plasma oestrone sulfate concentration could be a useful indicator of pregnancy within the first trimester of gestation in the cow.