Plasma concentrations of progesterone, oestrogens and prostaglandin F in maternal blood and corticosteroids and oestrogens in foetal blood of cows during dexamethasone-induced deliveries.

Infusing dexamethasone at rates of 0.1, 1.0 or 10 mg/day into 6 foetal calves at day 240 of gestation (2 calves per infusion rate), induced premature calving in a mean 12, 9 and 3 days respectively. Maternal plasma concentrations of progesterone, oestrone, oestradiol-17 beta and prostaglandin F or 13,14-dihydro-15-keto-prostaglandin F, and foetal plasma concentrations of oestrone, oestradiol-17 beta and corticosteroids were monitored until calving. The maternal hormone changes observed for all cows were a decline in progesterone, and a rise in both oestrogen and prostaglandin F concentrations before calving. Dexamethasone infused at a rate of 1.0 and 10.0 mg/day suppressed plasma corticosteroids in the foetus; however at 0.1 mg/day, foetal corticosteroids increased tenfold during the last 3 days before calving. At the lowest rate of infusion, dexamethasone had no effect on foetal oestrogen levels, but at rates of 1.0 and 10.0 mg/day there was a marked rise in foetal plasma levels of oestrogen.