Induction of parturition, progesterone secretion, and delivery of placenta in beef heifers given relaxin with cloprostenol or dexamethasone.
Sixty primiparous beef heifers from a crossbreeding study were used to examine the effects of inducing parturition with relaxin (3,000 U/mg) combined with cloprostenol (500 micrograms, i.m., n = 30) or dexamethasone (20 mg, i.m., n = 30) at Day 273, 10 +/- 1 days before expected parturition (Day 283). Heifers were assigned at random within cloprostenol and dexamethasone groups to receive relaxin (1 mg, n = 5/treatment), i.m. or in the cervical os (OS), at 0 h (the same time as cloprostenol and dexamethasone) or 24 h later. Eleven and six first-calving heifers and sixteen and nine second-calving cows also received cloprostenol + relaxin and cloprostenol + phosphate-buffered saline, respectively. Radioimmunoassay of daily plasma samples indicated an abrupt decrease in progesterone with time (p less than 0.001), from 7.5 +/- 0.50 to 1.0 +/- 0.30 ng/ml (mean +/- SE) within 48 h for all groups. The mean rate of progesterone decrease (ng/ml in 24 h) was accelerated (p less than 0.01) in relaxin-treated heifers (5.3 +/- 0.36), in contrast to dexamethasone- and cloprostenol-treated control heifers (2.8 +/- 0.40). Relaxin combined with cloprostenol or dexamethasone shortened the calving period in these heifers by reducing the interval between treatment and calving (33 vs. 56 h; p less than 0.01). The incidence and duration of retained placenta were reduced by 22 vs. 75% and 14 vs. 34 h for relaxin combined with cloprostenol or dexamethasone as compared with cloprostenol- or dexamethasone-treated controls, respectively (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)
Musah
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Department of Animal Science, Iowa State University, Ames 50011.
Schwabe
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Willham
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Anderson
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D000818:Animals; D002417:Cattle; D003008:Cloprostenol / Q000008:administration & dosage / Q000494:pharmacology*; D003907:Dexamethasone / Q000008:administration & dosage / Q000494:pharmacology*; D004338:Drug Combinations; D005260:Female; D007749:Labor Stage, Third / Q000187:drug effects*; D007751:Labor, Induced; D007743:Labor, Obstetric / Q000187:drug effects*; D010120:Oxytocics / Q000008:administration & dosage / Q000494:pharmacology*; D011247:Pregnancy; D011374:Progesterone / Q000378:metabolism*; D011461:Prostaglandins F, Synthetic / Q000494:pharmacology*; D012065:Relaxin / Q000008:administration & dosage / Q000494:pharmacology*
D004338:Drug Combinations; D010120:Oxytocics; D011461:Prostaglandins F, Synthetic; D003008:Cloprostenol; D011374:Progesterone; D003907:Dexamethasone; D012065:Relaxin