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Antiprogesterone, RU 486, Facilitates Parturition in Cattle^*

YANGFAN LI, RAUL PEREZGROVAS, OLADELE S. GAZAL, CHRISTIAN SCHWABE and LLOYD L. ANDERSON

Department of Animal Science, Iowa State University Ames, Iowa 50011
Department of Biochemistry, Medical University of South Carolina Charleston, South Carolina 29459

Address all correspondence and requests for reprints to: Dr. L. L. Anderson, Department of Animal Science, Iowa State University, 11 Kildee Hall, Ames, Iowa 50011.

Abstract

RU 486, a potent progesterone antagonist with high affinity for progesterone receptor, was used alone or in combination with relaxin in late pregnant cattle to determine its effect on induction of parturition. Cross-bred beef cattle were bred by artificial insemination. An indwelling cannula was inserted into a jugular vein on day 269 (expected term = day 283) for repeated blood sample collection. On day 277, the cattle were assigned randomly to three groups (n = 6 each): group 1 received RU 486 (2 mg/kg BW, im) at 0800 h on days 277 and 278; group 2 received the same RU 486 treatment plus 3000 U relaxin, injected sc at 0800 h on day 278; and group 3 served as controls and received vehicle injection. Parturition occurred 55 h after treatment in group 1 and 53 h after treatment in group 2 compared with 210 h in the controls (P < 0.01). The calves from treated groups were vigorous at birth, and their birth weights (32 and 33 kg in groups 1 and 2) were less than those of control calves (38 kg; P < 0.01). There was no incidence of difficult birth (dystocia) with RU 486 treatment compared with that in the controls. Placenta delivery averaged 6.5 h after birth in both RU 486-treated groups and did not differ from the control value (5 h). Plasma progesterone concentrations averaged 8.2 ng/ml during the pretreatment period for all animals. Progesterone started to decrease markedly by 1200 h on day 278, dropped to about 4 ng/ml by 2400 h that same day, and was at basal levels on day 279, the day of calving, in two hormone-treated groups. In sharp contrast, progesterone was maintained at about 6 ng/ml in placebo-treated controls during this period and did not decrease to basal levels until 2 days before parturition on day 286 (P < 0.01). Peak RU 486 in plasma was 7.2 ng/ml after the first injection and 14.3 ng/ml after the second injection, and averaged 7.9 ng/ml on the day of induced calving (day 279). Peak relaxin was 4.1 ng/ml after hormone injection. The results indicate that RU 486 alone or combined with relaxin precisely controlled the time of parturition in cattle in late pregnancy. Such treatment can be used to facilitate parturition and increase survival rates of neonatal calves without detrimental effects of dystocia, retention of placenta, and delayed postpartum fertility.

Footnotes

^* This work was supported by USDA ARS CSRS OGPS Competitive Grant 88-CRCR-37242-3918 and Iowa Biotechnology Council Grant AGD-86–2. Journal Paper J-14307 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA (Projects 2443, 2444, 2922, and 2273, the last a contributing project to North Central Regional Project NC-113).

Research Scientist on sabbatical leave from Chiapas Sheep Research Station, Universidad Autonoma de Chiapas, San Cristobal de Las Casas, Chiapas 29200, Mexico.

Freedom from Hunger Scholar, Rotary International, The Rotary Foundation, Evanston, IL.

Received March 8, 1991.

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