Total unconjugated oestrogen and progesterone concentrations in peripheral blood during pregnancy in the dog

Daily blood samples were withdrawn from three bitches throughout gestation and at intervals during parturition. The highest mean oestrogen value of 26-1 +/- 6-0 pg/ml was detected on the last day of pro-oestrus, and a lower post-oestrous peak occurred shortly after the maximum progesterone value of 17-0 +/- 1-0 ng/ml which was recorded 18 days after first service. No oestrogen rise was detected before parturition, and progesterone could not be detected after the end of parturition.