Plasma Concentrations of Insulin, Growth Hormone, and Prolactin in Pregnant Cows Subjected to Ovariectomy or Induced Parturition

Abstract

SUMMARY By using validated radioimmunoassay procedures, insulin ( ins ), growth hormone ( gh ), and prolactin ( prl ) were quantified in blood plasma collected from dairy cows late in gestation to 3 days after parturition. In control cows, plasma ins decreased during gestation to the day of calving (av gestation day 280) and then increased. Plasma gh in controls tended to increase during the last 2 weeks of gestation and then to decrease after parturition. Plasma prl in controls increased rapidly 12 to 24 hours before parturition and then decreased abruptly. Pregnant cows, which were ovariectomized on gestation day 218 and which delivered live calves after gestation day 250 (av 268 days), lactated normally. In ovariectomized cows, plasma concentrations of ins and prl were similar to concentrations in controls. After injections of dexamethasone and estradiol-17 β on gestation day 266, intact cows delivered live calves prematurely on gestation day 268; their subsequent lactations were normal. The foregoing injection treatment caused increased plasma ins during the 41 ± 2 hours from the time of injection to the time of calving, and plasma prl decreased less rapidly after parturition in treated cows than it did in controls. During the last 7 days before parturition, concentrations of plasma gh tended to be lower in ovariectomized and induced cows than in controls. Cows of both treated groups calved at an earlier stage of gestation than did controls, and this may have caused the difference in plasma gh values. Concentrations of plasma ins, gh , and prl collected 3 or more days before parturition were correlated with each other and with the major estrogens in plasma. Plasma ins, gh , and prl were not significantly correlated with plasma progesterone.