Between days 27 and 59 after artificial insemination (AI), 189 ultrasonographic pregnancy diagnoses were made in 56 dairy cows using a 7.5 MHz linear-array rectal transducer. Blood samples were withdrawn from a jugular vein on the day of Al, on day 21, and after each ultrasonographic examination between days 27 and 31, days 34 and 38, days 41 and 45 and days 55 and 59 after AI. Plasma concentrations of bovine pregnancy- associated glycoprotein 1 (bPAG-1) were measured by radioimmunoassay. The results showed that before day 31, ultrasonographic scanning was not very sensitive because six of the 30 calving cows were incorrectly diagnosed as non-pregnant. In five of these animals, the uterus was located far cranial to the pelvic inlet. Five of the cows examined between days 27 and 31 were pregnant on the basis of plasma bPAG-1 levels on the same day, using 0.5 ng/ml as the cut-off point. Plasma levels of bPAG-1 and progesterone proved that four of the cows which had early positive ultrasonographic diagnoses but did not produce a calf, were pregnant when they were examined.
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