PROGESTERONE CONCENTRATIONS IN PERIPHERAL PLASMA OF MENZ SHEEP DURING GESTATION AND PARTURITION

Progesterone concentrations were monitored weekly during gestation, averaging 151 +/- 2 d, in peripheral plasma of Menz ewes using enzyme immunoassay. Mean hormone concentrations were basal, less-than-or-equal-to 1.0 ng/ml at service, but increased to 4.7 ng/ml on d 14 and remained elevated throughout pregnancy, differing significantly between ewes and stage of gestation (P < 0.01), but not due to number or sex of foetuses (P > 0.10). Progesterone production was also lowly related to weight of lambs at birth (r=0.24). Progesterone level increased to 8.4 +/- 0.3 ng/ml by d 35 (first trimester), 13.2 +/- 0.4 ng/ml by d 75 (second trimester) and 13.8 +/- 1.0 ng/ml by d 126 (third trimester). This was followed by a gradual decline during the last three weeks which accelerated 3 d prepartum to reach below 1.0 ng/ml 2 to 4 d after lambing. It was concluded that elevated progesterone levels 18 to 22 d after mating indicate continued luteal function and/or pregnancy in Menz sheep.