title: Mifepristone (RU 486) induces parturition in primiparous beef heifers and reduces incidence of dystocia.
abstract: Crossbred beef heifers (n = 21) were artificially inseminated and on d 268 (expected parturition = d 283) heifers were fitted with an indwelling jugular catheter for sequential blood sampling from d 270 to 278. Heifers were assigned randomly to three treatment groups (n = 7) on d 277: Group 1 received the synthetic steroid mifepristone (RU 486) alone, Group 2 received RU 486 plus relaxin, and Group 3 received placebo treatment. Parturition occurred 43 h after treatment in Group 1, 52 h in Group 2, and 182 h in Group 3, and hormone treatment reduced treatment-to-calving interval compared with diluent treatment (P < .01). Calf birth weights were lower in hormone-treated than in placebo-treated heifers (P < .025), but all calves were vigorous at birth. The incidence of dystocia was lower (P < .05) in heifers in Groups 1 and 2 than in controls. Conversely, placental retention longer than 24 h was observed in hormone-treated heifers, and none occurred in the control group. The RU 486 reduced circulating progesterone concentrations in treated heifers, whereas progesterone concentration remained increased in control (P < .01). The results show that RU 486 alone or combined with relaxin induces delivery in late-pregnant heifers. Hormone treatment promotes calving ease with a markedly reduced incidence of the detrimental effects of dystocia, which may be a serious problem in first-calf heifers.
authors.affiliation: Department of Animal Science, Iowa State University, Ames 50011-3150, USA.
authors.forename: B J
authors.initials: BJ
authors.lastname: Dlamini
authors.forename: Y
authors.initials: Y
authors.lastname: Li
authors.forename: L L
authors.initials: LL
authors.lastname: Anderson
mesh_terms: D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology / Q000517:prevention & control*; D004420:Dystocia / Q000453:epidemiology / Q000517:prevention & control / Q000662:veterinary*; D005260:Female; D015994:Incidence; D007743:Labor, Obstetric / Q000097:blood / Q000187:drug effects* / Q000502:physiology; D008600:Menstruation-Inducing Agents / Q000494:pharmacology*; D015735:Mifepristone / Q000494:pharmacology*; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000097:blood / Q000187:drug effects* / Q000502:physiology; D011374:Progesterone / Q000097:blood; D011863:Radioimmunoassay; D012065:Relaxin / Q000494:pharmacology
chemical_list: D008600:Menstruation-Inducing Agents; D015735:Mifepristone; D011374:Progesterone; D012065:Relaxin