Diagnosis of pregnancy by radioimmunoassay of a pregnancy-specific protein in the plasma of dairy cows

The accuracy and efficiency of progesterone (P4) and bovine pregnancy-specific protein B (bPSPB) radioimmunoassays (RIA) in detecting pregnant and nonpregnant dairy cows were compared at different stages of pregnancy. The study included 145 French Friesian heifers and cows from a single herd. A total of 175 artificial insemination (A.I.) and blood sampling procedures were performed. Animals were bled 24 d post AI for P4 RIA. They were bled at 24, 26, 30 to 35, and 70 +/- 9 after AI for bPSPB RIA. Females were declared nonpregnant when plasma P4 concentrations were lower than 1.5 ng/ml. With the bPSPB RIA, cows were nonpregnant when at least one of the B Bo x 100 replicates was higher than 95% in the RIA. When compared with palpations per rectum at 70 d, the accuracy of positive diagnoses (no. positive and pregnant/no. positive diagnoses) by P4 RIA at Day 24 was 67.2% (82 122 ). The accuracy of negative diagnoses was 98% (52 53 ). Accuracy of positive diagnoses by bPSPB RIA increased with gestation age (P<0.05) from 86.2% (50 58 ) on Day 24 to 98.8% (83 84 ) at time of palpation per rectum. Accuracy of negative diagnoses increased (P< 0.001) from Day 24 (71.8%; 84 117 ) to Days 30 to 35 (100%, 83 83 ). Efficiency in detecting nonpregnant females was much higher (P < 0.001) with the bPSPB RIA on Days 30 to 35 (90.2%; 83 92 ) than with the P4 RIA on Day 24 (56.5%, 52 92 ). It is concluded that 30 days after AI, the bPSPB RIA is an efficient test both for pregnancy prediction and detection of nonpregnant dairy cows.