The Veterinary Record, Vol 139, Issue 8, 187-191
Copyright © 1996 by British Veterinary Association

Norgestomet implants, plasma progesterone concentrations and embryo transfer pregnancy rates in cattle

¹ Department of Animal and Feed Technology, SAC (Aberdeen), 581 King Street, Aberdeen AB9 1UD
² Department of Veterinary Clinical Science and Animal Husbandry, University of Liverpool Veterinary Field Station, Leahurst, Neston, South Wirral L64 7TE

A study was undertaken to test the hypothesis that supplementation with exogenous progestagen at the time of embryo transfer would enhance pregnancy rates in recipients. Two-hundred-and-seventy-two oestrus-synchronised crossbred heifer and cow recipients received 200 grade 1 and 72 grade 2 Simmental embryos transferred non-surgically. Heparinised blood samples were taken on day 6 and day 7 (oestrus = day 0) for the assessment of the endogenous plasma progesterone concentration. Half the recipients received an ear implant impregnated with 3 mg norgestomet on the day of embryo transfer. The pregnancy rates were 51·9 and 49·6 per cent for the norgestomet-treated and control groups, respectively. The pregnancy rate for grade 1 embryos was 56·0 per cent and for grade 2 embryos 36·1 per cent (P<0·01). The breed of recipient, weekday of transfer, operator and condition score had no effect on pregnancy rate. The maiden heifers had a higher pregnancy rate (54·2 per cent) than the cows (46·2 per cent). The mean plasma progesterone concentrations of the pregnant and non-pregnant groups on day 6 were 6·7 ng/ml and 6·6 ng/ml, respectively, and 7·6 ng/ml in both groups on day 7.