Hormonal pattern in the blood of eight mares during the first weeks of pregnancy

The hormonal pattern in the blood of eight mares was studied during the first 5 to 6 weeks of pregnancy; in two of the eight animals early embryonic death was established on D-28 and on D-40, respectively. Progesterone peaks were found in the blood around D-5, D-12 to D-10, and D-17 to D-18. It is suggested that the decrease of the progesterone concentrations in the blood during the intermediate periods is due to the action of oestrogens. During the period from D-18 to about D-34 the concentrations both of progesterone and of pregnenolone were low in the pregnant mares. Thereafter a small increase of the progesterone content was observed. Sometimes rather large amounts of the compound "5.4", an isomer of pregnenolone, were found, indicating the presence of follicles containing oestradiol-17beta or possibly a stimulated uterus. It is suggested that early embryonic death may be expected. a. if the progesterone concentration in the blood is low on D-17 to D-18; b. if there is no increase of the progesterone or the "5.4" concentrations during the period from D-34 to D-37. A relatively high pregnenolone level on these days indicates reduced conversion of pregnenolone into progesterone.