This experiment was carried out to determine the progesterone concentration of bovine plasma by liquid phase double antibody enzyme immunoassay. The optimum conditions of assay-system, enzyme conjugate and gelatin were investigated. The sensitivity, recovery rate and reproducibility by this assay were also analyzed. The suitable supplementation level of gelatin was 0.2 %. As the gelatin level increased to 1 %, coefficient variation of interassay was shown to be irregular. The optimum dilution rate of enzyme conjugate was 30 times. Enzyme activity was greatly fluctuated depending on the minor condition of enzyme conjugate technique. Therefore, it was considered to be checked when determined. The sensitivity of the assay was 12 pg/tube. Recovery rate was decreased when the amount of sample was too little or too much, but the recovery rate was high as 97.8 % when the amount of sample was between 50 and 200 micro l. Mean intra-assay and inter-assay coefficient of variation was 4.5 % and 5.9 %, respectively. By using liquid phase double antibody enzyme immunoassay, progesterone in plasma can be detected, and also this assay system is applicable to study the physiological function of progesterone and diagnosis of reproductive disorders

A total of 13 synchronized dairy cattle (Holstein) were used to determine pregnancy rates in relation to plasma progesterone, estradiol-17-beta levels and serum chemical values on the day of last PGF 2 alpha injection and day of frozen/thawed bovine embryo transfer. The pregnancy rate of recipients with 1.0-4.0ng/ml of progesterone levels at the day of last PGF 2 alpha injection was higher than that of recipients with below 1.0ng/ml or above 4.0ng/ml of progesterone levels. On the day of transfer, optimal progesterone levels were between 1.0ng/ml and 4.0ng/ml coinciding with a pregnancy rate of 88.9 %. Pregnancy rate decreased when progesterone levels were below 1.0ng/ml (33.3 %) or above 4.0ng/ml (0 %). Corpus luteum grade did not affect pregnancy rate and this result revealed that manual palpation of corpus luteum was not valid criterion of corpus luteum function. Progesterone levels as well as pregnancy rate did not significantly differ whether the corpus luteum was on the right (1.62 +- 1.33ng/ml; 63.5 %) or left ovary (1.99 +- 0.61ng/ml; 85.0 %). Estradiol-17-beta levels were not significantly different between pregnant and nonpregnant recipients, but estradiol-17-beta levels (82.2 +- 13.5 VS. 72.3 +- 10.1pg/ml) were higher at below 1.0 ng/ml of progesterone. Total cholesterol levels on the day last PGF 2 alpha injection and day of transfer did not affect pregnancy rate. Calcium and inorganic phoshorus levels belonged to normal range in most of the recipients. These range did not affect pregnancy rate. In reviewing above results, plasma progesterone levels (1.0-4.0ng/ml) at the time of transfer are diagnostic value for screening recipients prior to transfer of frozen/thawed bovine embryos