Detection of pregnancy by radioimmunoassay of a pregnancy serum protein (PSP60) in cattle.

The accuracy and efficiency of pregnancy diagnoses in cattle by pregnancy serum protein (PSP60) radioimmunoassay, a progesterone radioimmunoassay or oestrus detection were compared. Blood samples were taken from 349 suckling heifers and cows (1,191 inseminations) at 28, 35, 50 and 90 d post-insemination for PSP60 determination and at 22-23 d for progesterone. Females were declared nonpregnant when plasma PSP60 concentration was lower than 0.2 ng/ml at 28, 35 and 50 d and 0.5 ng/ml at 90 d. When compared with rectal palpation at 90 d, the accuracy of positive (negative) diagnoses by progesterone assay was 80% (100%) in heifers and 75% (99%) in cows. The accuracy of positive diagnoses by PSP60 assay increased with gestation stage from 90% on d 28 in heifers (74% in cows) to 100% (99% in cows) at the time of rectal palpation. This accuracy was 84% on d 28 in cows when the interval from calving to blood sampling was higher than 115 d. Whatever the stage, the accuracy of negative diagnoses was higher than 90%. Efficiency in detecting pregnant or nonpregnant females on d 28 was equivalent to the progesterone assay. The method for detecting oestrus applied in this experiment was as efficient as the PSP60 or progesterone test at any stage of gestation. The PSP60 test is very flexible, which makes its use particularly interesting in naturally mated suckling herds because of the uncertainty regarding the date of fertilization.