[Changes in the concentration of estrone, estradiol and estradiol in the blood of pregnant ewes].

A chemical method was used for the study of the concentration of the three main groups of oestrogens in the blood of five ewes after mating in natural heat. The concentration values of all the three groups of oestrogens was found to increase in proportion with the length of gravidity. From the 30th to the 140th day of gravidity the average concentration values of oestrone increased from 309 to 1380 ng per 100 ml blood, those of oestradiol from 48 to 192 ng per 100 ml blood. Significant changes were recorded in oestrone between the 50th and 60th day and between the 130th and 140th day of gravidity; in oestradiol and oestriol such changes occurred on the 140th day of gravidity.