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Concentrations of Hormones in Blood and Milk during and after Induction of Parturition in Beef Cattle with Dexamethasone and Estradiol-17ß^{1, 2,}

Purdue University, West Lafayette, Indiana 47907

Abstract

Twenty-three Hereford and 10 Hereford-Simmental crossbred cows bred to Simmental bulls were used to compare effects of dexamethasone (DEX) and estradiol-17ß (E₂ß) on parturition and on hormone changes in whole blood and mammary secretions. Treatments were: Group 1–none (five cows); Group 2–30 mg DEX (eight cows); Group 3–30 mg DEX + 25 mg E₂ß at the same time (11 cows); Group 4–30 mg DEX + 25 mg E₂ß 12-hr before and 12-hr after DEX (nine cows).

Cows in Group 1 calved 291 ± 2.1 days after breeding as compared to 281 ± .6, 279 ± .6 and 279 ± .8 dyas for Groups 2, 3 and 4, respectively (P<.01). Average interval from DEX treatment to calving was 56 hr for DEX alone and 43 hr for DEX and E₂ß (P<.01). There were no differences between treatments for calving difficulty, calf viability, average daily gain of calves, postpartum illness of cows and ovarian function at 40 ± 2 days after calving. Group differences were nonsignificant regarding whole blood and milk progesterone, estrone and estradiol concentrations and blood prolactin at each period studied. The periods were pretreatment (Day –2), next day after treatment (Day –1), 1 to 8 hr after calving (Day 0), Day 1 (milk only) and Days 2 and 5. In each group, average milk and blood progesterone decreased from Day –2 to Day 0 (P<.01), estrone and estradiol decreased from Day 0 to Days 1 or 2 (P<.01), and prolactin was lower on Day –2 and Day 5 as compared to the highest day (Day 0; P<.01). Concentrations of steroids in blood and mammary secretions were positively correlated (P<.01). Injected E₂ß did not significantly change levels of estrone or estradiol in blood or milk.

¹ Journal Paper 5699, Purdue University Agricultural Experiment Station, West Lafayette, Indiana 47907. A contribution from the Department of Animal Sciences.

² The authors are indebted to Dr. G. D. Niswender, Dr. R. D. Randel, and Dr. P. V. Malven for supplying antibodies used for radioimmunoassay of progesterone, estrogen and prolactin, respectively, to Dr. P. V. Malven for assay of blood prolactin and to Mrs. Doris Blair for assistance with hormone assays.

³ Present address: Department of Dairy Husbandry, University of Missouri, Columbia 65201.

⁴ Superintendent, Lynnwood Purdue Agricultural Center, Carmel, Indiana 46032.

⁵ Department of Veterinary Science.