Enhanced Precision of Estrus and Luteinizing Hormone After Progesterone and Prostaglandin in Heifers

Abstract

Objectives were to determine if low progesterone and increased basal luteinizing hormone for 3 d after injecting prostaglandin F2α would affect precision of preovulatory surges of luteinizing hormone and onset of estrus in Holstein heifers. In experiments 1 and 2, heifers received progesterone devices for 10 d and prostaglandin F2α on the 7th d after inserting progesterone device. For controls, progesterone devices were removed when prostaglandin F2α was injected, and control devices were installed for 3 d. In experiment 1, jugular blood was sampled every 2 or 4 h from injection of prostaglandin F2α until 108 h after removing progesterone to determine basal and peak secretion of luteinizing hormone. In treatment heifers, basal luteinizing hormone tended to increase, and intervals to peak secretion of luteinizing hormone were shorter and more precise than for controls. In experiment 2, heifers were observed for estrus for 30 min every 4 h for 96 h after removing progesterone devices. Intervals to onset of estrus for experimental heifers were shorter and more precise than for controls. After exogenous prostaglandin F2α, 1 to 2 ng of progesterone per milliliter of serum for 2 to 3 d allows increased basal luteinizing hormone and is associated with increased precision of preovulatory secretion of lutenizing hormone and onset of estrus. This may be an acceptable method to control ovulation precisely for fixed time insemination of cattle. © 1986, American Dairy Science Association. All rights reserved.