75 DETECTION OF EMBRYONIC DEATH BY MONITORING OVARIAN STEROIDS BALANCE AND ULTRASONOGRAPHY IN JAPANESE BLACK CATTLE

In beef cattle, 20 to 44% embryonic loss occurs during the early stages of pregnancy (Humblot et al. 2001). However, the mechanism of early and late embryonic death is not clear. We investigated occurrence of embryonic death by monitoring ovarian hormones dynamics and checking for the presence of the conceptus after artificial insemination or embryo transfer in beef cattle. Twenty Japanese black females were inseminated (AI) and 12 females were transferred with 1 embryo (ET). Blood samples were collected on Days 21, 24, 28, 38, 48, 58, and 68 post-oestrus (oestrus = Day 0) and then stored at –30°C. Progesterone (P4) and oestradiol (E2) plasma concentrations were analysed using a chemiluminescent immunoassay. On each day of blood sampling, ovaries and presence of a conceptus in the uterus were monitored by ultrasonography. At Day 24 post-oestrus, the presence of the fetus was detected in 8 females (AI, n = 6; ET, n = 2), whereas only 3 females were confirmed to be pregnant at Day 28 and Day 38 post-oestrus. No embryo loss was seen at later stages of pregnancy (Days 48, 58, and 68 post-oestrus). At Day 21 post-oestrus, the conceptus could not be detected by ultrasonography but the E2/P4 ratio provided indication on the pregnancy status of the females that were classified as pregnant (n = 8) or not pregnant (n = 24) at day 24 post-oestrus (1.7 ± 2.2 versus 28.0 ± 34.2 respectively; mean ± s.d.). In the nonpregnant females compared with the pregnant ones at Day 24 post-oestrus, P4 declined below 1 ng mL–1 (0.6 ± 0.2 ng mL–1 v. 8.6 ± 3.9 ng mL–1), whereas E2 blood level remained stable (15.7 ± 21.9 v. 18.1 ± 1.1 pg mL–1). The decrease in P4 levels led to an increase in E2/P4 ratio (1.3 to 37.3 on Day 24). Our study suggests that a large proportion of embryo loss (75%) occurs before Day 24, whereas an additional 16% loss was seen between Day 24 and Day 28 post-oestrus. This embryo loss was shown to be associated with the altered balance of ovarian hormones.