75 COMPARISON OF THE DG29^TM ENZYME-LINKED IMMUNOSORBENT ASSAY KIT COMPARED WITH TRANSRECTAL ULTRASONOGRAPHY FOR EARLY PREGNANCY DIAGNOSIS FOLLOWING TRANSFER OF JAPANESE BLACK CATTLE EMBRYOS

Abstract

In commercial embryo transfer industry, accurate early detection of pregnant and nonpregnant cows plays a key role in achieving an optimum calving-to-conception interval. The DG29^TM enzyme-linked immunosorbent assay (ELISA) kit (Conception, Animal Reproduction Technologies, Beaumont, Canada) measures the level of pregnancy-related glycoproteins in blood that are linked to pregnancy. Here, we compared the DG29 kit with transrectal ultrasonography (TU) to evaluate the possibility of the clinical application of the ELISA kit for early pregnancy diagnosis. Embryos recovered from superovulated Japanese Black cows were transferred to 110 recipient Holstein heifers on Day 6 to 8 of the oestrous cycle (oestrus = Day 0). Pregnancy was diagnosed between Day 29 and Day 40 by TU with a 5.0/7.5-MHz linear array transducer (Tringa, Pie Medical Equipment B.V., Maastricht, the Netherlands). Blood samples were collected from the tail vein or artery into vacuum serum tubes after TU and serum was separated and stored at –30°C until the ELISA was performed. The ELISA results were interpreted as positive (pregnant, >1000 pg mL^–1) or negative (nonpregnant, <300 pg mL^–1). Ninety-nine of the 110 heifers were judged as pregnant or nonpregnant by TU. Seventy-six of the 99 heifers were judged as pregnant, in which fetuses were visualised clearly in the uterine horn. The following measures, sensitivity, specificity, predictive value and accuracy of pregnancy outcomes based on the ELISA results, were assessed by comparing with those based on the definite TU results. The values for sensitivity and specificity were 100% (76/76) and 91.3% (21/23), the positive and negative predictive value were 97.4% (76/78) and 100% (21/21), respectively and accuracy was 98.0% (97/99). On the other hand, chorioallantoic fluids in 11 of the 110 heifers were detected by TU around Day 30 of gestation, but fetuses were not identified or were unclearly visualised, which suggests that the embryos died during the peri-implantation period after transfer. Ten of the 11 heifers were classified as pregnant by the ELISA, but only 3 heifers were identified as pregnant with reexamination by later TU, which indicates that the pregnancy-related glycoproteins residue from embryo mortality was detected by the DG29 kit. However, the negative predictive value of the DG29 kit was 100% in this study. In conclusion, except for early embryonic death, the DG29 kit was highly accurate and suitable for clinical application in early pregnancy determination following transfer of Japanese Black cattle embryos.