NORGESTOMET IMPLANTS, PLASMA PROGESTERONE CONCENTRATIONS AND EMBRYO-TRANSFER PREGNANCY RATES IN CATTLE

A study was undertaken to test the hypothesis that supplementation wit h exogenous progestagen at the time of embryo transfer would enhance p regnancy rates in recipients. Two-hundred-and-seventy-two oestrus-sync hronised crossbred heifer and cow recipients received 200 grade 1 and 72 grade 2 Simmental embryos transferred non-surgically. Heparinised b lood samples were taken on day 6 and day 7 (oestrus = day 0) for the a ssessment of the endogenous plasma progesterone concentration, Half th e 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 gra de 2 embryos 36.1 per cent (P<0.01). The breed of recipient, weekday o f transfer, operator and condition score had no effect on pregnancy ra te, The maiden heifers had a higher pregnancy rate (54.2 per cent) tha n the cows (46.2 per cent), The mean plasma progesterone concentration s 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.