STEROID HORMONE LEVELS IN BEEF COWS DURING PREGNANCY TERMINATING IN NORMAL CALVING OR ABORTION AND WITH SINGLE OR MULTIPLE OVULATION

Abstract

Plasma estrogen and progesterone levels were studied in cows bearing one or more embryos during pregnancies that ended either normally or by abortion. Different pregnancy rates were obtained by administering 800 or 1,600 IU pregnant mare serum gonadotrophin to cows fed either a low or high energy ration. With an increasing dose of gonadotrophin, increases were observed in the percentage of animals responding, the ovulation rate and the variability in individual response. In calving cows bearing more than one embryo, the levels of progesterone and of estradiol-17β were consistently higher during pregnancy than in calving cows bearing only one embryo. The concentration of estrone was also increased in the former group but only during the first trimester. In multi-ovulating cows that aborted, the high progesterone levels found at day 10 after mating were soon followed by a marked decrease: this forecast the abortion which always occurred, although often at a much later date; estrone levels tended to be lower in aborting cows than in calving cows, although there was considerable variation between individual patterns. Estradiol-17β levels were also low in aborting cows, and the gradual increase throughout pregnancy that was characteristic of calving cows was always absent. These results show that early in pregnancy in cows that are to abort the progesterone secretion cannot be maintained and that estradiol, although it is less abundant than estrone, is a better indicator of the physiological state of pregnancy.