Reproductive Steroids in the Bovine. I. Relationships during Late Gestation

Abstract

MELLIN, Erb and Estergreen (1966) found a substantial increase in the rate of excretion of estrogen in urine just prior to parturition and a rapid decrease after parturition. Short (1958) reported that the progesterone content of the blood remained constant from 32 to 256 days of pregnancy but was markedly reduced just prior to calving. However, Erb et al. (1968) have questioned that levels of progesterone in blood always decline prior to parturition in the COW. Causes of variation in period of gestation and the initiation of parturition have been topics for research for many years. Differences in period of gestation have been associated with breed and age of cow, weight and sex of calf, and sire of calf (Alexander, 1950; Brakel, Rife and Salisbury, 1952; Legault and Touchberry, 1962). It was the purpose of this study to determine if the length of gestation in cows was associated with variations in the pattern and rate of excretion of estrogens in urine and levels of progesterone in blood plasma.