Abstract:
The objective of this study was to determine the peripheral plasmaconcentration of oestrone sulfate during early gestation in the cow with asensitive assay system. Five Holstein heifers were inseminated on oestrus andbled from the jugular vein at regular intervals until 100 days of gestation.Oestrone sulfate, oestrone and oestradiol-17β in blood plasma wereextracted with a reverse-phase cartridge and each measured by specificradioimmunoassay. Oestrone sulfate in bovine circulation started to increasearound 50 days of gestation, whereas oestrone and oestradiol-17β remainedat basal concentrations for 80 days. The plasma concentration of oestronesulfate increased gradually and linearly from 50 days of gestation, and wasdrastically elevated after 80 days of gestation before the increase inunconjugated oestrogens. The rate of increase from 80 to 100 days was thegreatest for oestrone sulfate concentration among all oestrogens. Theseresults suggest that plasma oestrone sulfate concentration could be a usefulindicator of pregnancy within the first trimester of gestation in the cow.