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Use of Estrogen with Dexamethasone for Inducing Parturition in Beef Cattle^{1, 2,}

University of Missouri, Columbia 65201

Abstract

Induced parturition was studied in 28 mature Charolais and Hereford cows randomly assigned to three treatment groups. Control cows were designated as Group A and cows in Groups B and C were injected with 20 mg dexamethasone 8 to 14 days prior to the expected calving date. Cows in Group C also received 6 mg estradiol benzoate in conjunction with dexamethasone. Blood samples were collected prior to and following parturition for subsequent hormone analysis and observations were made on the occurrence of retained placenta. Plasma progestins and corticoid levels were determined by the competitive protein binding assay and a radioimmunoassay was used to determine plasma estradiol concentrations. Of 19 cows injected with dexamethasone, 17 calved 38 to 69 hr. following injection. The placental membranes had been expelled at examination 3 days after calving in six of nine, two of eight and seven of nine cows in Groups A, B and C, respectively. There was no significant change in plasma corticoid levels in control cows during the experimental period, however, corticoid levels were suppressed for at least 2 days following the injection of dexamethasone. The injection of dexamethasone resulted in a rapid and significant drop in plasma progestin concentration to a level not significantly different from control animals at parturition. Plasma estradiol levels increased significantly from day -2 to day 0 in controls and cows injected with estradiol benzoate, whereas there was no change in estradiol levels from injection to calving in cows receiving dexamethasone alone. A precipitous drop in plasma estradiol level occurred following parturition in all treatment groups.

¹ Contribution from the Missouri Agricultural Experiment Station. Journal Series No. 6702. Approved by the Director.

² The authors wish to acknowledge their appreciation to Mr. Joe Swisher, Research Specialist, for his assistance in handling of the experimental animals; Dr. E. S. Hilderbrand for assistance in statistical analysis of the data; and to Dr. Guy Abraham, Harbor General Hospital, Torrance, California, for supplying Antibody S-52 #5 for estradiol determination.

³ Department of Dairy Husbandry, University of Missouri-Columbia.

⁴ Department of Animal Husbandry, University of Missouri-Columbia.

⁵ Department of Veterinary Medicine and Surgery, University of Missouri-Columbia.