Prepartum and Postpartum Levels of Progesterone and Estradiol in Beef Heifers Fed Two Levels of Energy

Abstract

Twelve first-calf, 2-year-old, Hereford heifers were randomly assigned in equal numbers on two levels of energy (17.6 Mcal DE/day and 11.4 Mcal DE/day) beginning 100 days prepartum. Jugular blood was collected three times weekly from the heifers starting 14 days before parturition, and continuing through the postpartum period until 20 days following the first estrus. There was no significant effect of nutrition on peripheral levels of progesterone or estradiol either prior to or following parturition. Progesterone levels declined from 2.0 to 2.5 ng/ml during late gestation to 0.7 to 0.9 ng/ml at parturition and remained low until just preceding the first postpartum estrus. Progesterone levels were higher immediately preceding the first postpartum estrus in those heifers that conceived. A short estrous cycle (6 to 8 days) was observed in three heifers following first estrus. In these, progesterone levels failed to exceed 0.6 ng/ml. Estradiol levels also declined sharply at parturition and remained in the range of 4 to 8 pg/ml during the postpartum period rising at the occurrence of first postpartum estrus. Copyright © 1974. American Society of Animal Science. Copyright 1974 by American Society of Animal Science.