PROGESTERONE IN THE PERIPHERAL BLOOD OF GUERNSEY AND FRIESIAN COWS DURING PROLONGED GESTATION

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Abstract
Progesterone was determined in the peripheral blood of five cows exhibiting a prolonged gestation period of up to 92 days beyond the normal duration of pregnancy (285 days). The blood progesterone levels during the period of prolonged gestation were similar to those found in normal cows during mid-pregnancy, however, there was no sign of a fall in the progesterone level just prior to the expected date of delivery, which is so characteristic of normal cows. The signidicance of these findings is discussed in relation to the mechanisms that might initiate parturition in the cow.