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

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. Twohundred‐ 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