Progesterone in Bovine Reproduction: A Review

Abstract

Portions of an extensive literature were reviewed to evaluate the status of our knowledge relative to progesterone in the bovine. Studies related to the secretion and metabolism of progesterone have been hampered by the lack of chemical methods sufficiently sensitive and specific to quantitate the hormone in small samples. Certain bioassays are extremely sensitive but lack specificity and have undefined limits of error. Spectrophotometric determination of progesterone or progesterone derivatives appears specific but is sensitive to only 0.1–0.5 μg. Fluorometric, gas chromatographic, and double-isotope derivative methods promise sensitivity to 0.01 μg with adequate specificity and precision. Progesterone and 20 β-hydroxy-Δ4-pregnene-3-one appear to be the principal progestins in the corpus luteum (CL) of cycling and pregnant cows. Progestins have also been reported in bovine ovaries, adrenals, and blood. The CL appears to be the most important source of progesterone throughout bovine pregnancy. The CL from a previous cycle contains measurable progesterone for two or three days after estrus. Progestin in the CL and ovarian vein blood declines rapidly during proestrus from maximum levels observed 14–16 days post-estrus. In the pregnant cow, CL progestin levels decline about 40% from mid-cycle levels by 42–56 days of pregnancy, further decline slowly until 200 days, then rise again to the 28-day level; after 250 days, a decline to parturition begins. Similar changes are seen in blood levels of the hormones during pregnancy. Progesterone appears important in pregnancy maintenance, expression of estrus, normal cyclic function, and in hypophyseal-gonad interrelationships. © 1965, American Dairy Science Association. All rights reserved.