INVESTIGATIONS INTO THE COURSE OF PROGESTERONE-CONCENTRATION, ESTROGEN-CONCENTRATION AND ECG-CONCENTRATION DURING NORMAL AND IMPAIRED PREGNANCY IN THE MARE

Blood plasma samples were collected weekly after mating from 38 mares and a comprehensive picture covering the whole period of pregnancy was obtained for progesterone, free and conjugated estrone equivalents, e CG and cortisol. The appearance and disappearance of eCG between weeks 5 and 20 was correlated with the formation and regression of suppleme ntary corpora lutea; the progesterone plateau observed thereafter and the increase prior to parturition were attributed to cross-reactivity of the antiserum used with other progestagens. Conjugated estrone equi valents showed a first increase concomitant with the formation of supp lementary corpora lutea, the second increase commenced during weeks 10 -12, reaching maximum levels around 700 ng/ml plasma in week 22. Free estrone equivalents did not start to increase before week 14. Progesta gens and estrogens showed a precipitous decline one day prior to partu rition while cortisol did not change; however, cortisol levels were hi gher (p < 0.001) during weeks 10-17 compared to the other periods of p regnancy. Additionally, in two mares an extended period of eCG product ion until parturition or abortion (week 42) was observed. In cases of embryonic resorptions the levels of progesterone and conjugated estron e equivalents decreased rapidly, eCG levels, however, remained elevate d and apparently did not interfere with resumption of cyclic ovarian a ctivity. Compared to normal pregnancies, the progestagen and estrogen levels were higher between week 22 and the week prior to abortion (wee k 31-42) in the five aborting mares. In three mares defined as pseudop regnant, luteal function was extended up to 77 days after mating but n o rise of conjugated estrone equivalents or eCG occurred.