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.

Use of the progesterone (P4) receptor antagonist aglepristone to characterize the role of P4 withdrawal for parturition and placental release in cows

“…Clinical observations indicated that dystocia was due to an insufficient myometrial activity and a poor widening of the posterior birth canal. In contrast to our study, no dystocia was observed after the induction of parturition in multiparous beef cows using mifepristone starting on day 277 (Li et al 1991), and the incidence was low in beef heifers (Dlamini et al 1995). The reason for this significant difference between these results is not clear but may be related to the time when antiprogestin treatment was started.…”

“…The prepartal course of body temperature in D272CAp cows clearly resembles features described for the phase preceding normal term characterized by a transient decrease of 0.4 8C (48-22 h; Birgel et al 1994) and the absence of diurnal variation (48-8 h; Lammoglia et al 1997). The time between the onset of antiprogestin treatment and birth (48.7G7.5 h) is in the same range as reported after the initiation of parturition using the similar type antiprogestin, mifepristone, on days 277 and 278 in beef cows (55G3 h; Li et al 1991) or beef heifers (43G7 h; Dlamini et al 1995).…”

“…A similar situation has been postulated for the dog, where, depending on the time of antiprogestin treatment, parturition with impaired or efficient (Baan et al 2005) expulsion of the puppies had been observed. The assumption that in our study antiprogestin treatment was started at an earlier stage of readiness for parturition compared with the study by Li et al (1991) and Dlamini et al (1995) is also substantiated by the observation that in our experiment calves from Ap-treated animals and from day 272 controls were viable but needed considerable clinical care during the first week after Figure 4 Concentrations of progesterone, estradiol 17b, estrone, and estrone sulfate in four untreated control cows during late gestation and around normal term. Gestational length was 280.5G1.3 days, and the placenta was released within 12 h after spontaneous expulsion of the calves.…”

“…The reason for this significant difference between these results is not clear but may be related to the time when antiprogestin treatment was started. Although the mean gestational length in beef cattle used by Li et al (1991) and Dlamini et al (1995) was slightly longer than in Holstein cows used in our study (beef cows: 286G2.3 days; beef heifers: 284G1.5 days; Holstein: 280.5G1.3 days), uterine activation by upregulating a cassette of contraction-associated proteins and/or the conditioning of the systems providing uterotonins such as oxytocin and PGF 2a (Whittle et al 2001) -presumably by signals from the fetal side -may have been substantially different at the onset of antiprogestin treatment between the two experimental settings. A similar situation has been postulated for the dog, where, depending on the time of antiprogestin treatment, parturition with impaired or efficient (Baan et al 2005) expulsion of the puppies had been observed.…”

“…Progesterone withdrawal in bovine parturition parturition to survive, whereas Li et al (1991) and Dlamini et al (1995) reported that calves from their experiments born around day 279 were vigorous.…”