Early pregnancy diagnosis based on luteal morphology and blood flow on Days 17-21 post-artificial insemination in Japanese Black cattle.

The present study was conducted to evaluate the applicability of corpus luteum (CL) morphology and blood flow for early pregnancy diagnosis on Days 17-21 post-artificial insemination (AI) in Japanese Black (JB) cattle. Ultrasound examinations were performed on 230 inseminated JB cattle (202 cows and 28 heifers) to evaluate CL morphological characteristics [CL area, CL tissue area, presence/absence of a central cavity, and central cavity area (CCA)] and blood flow area (BFA) on Days 17 (n = 46), 18 (n = 45), 19 (n = 46), 20 (n = 47), and 21 (n = 46) (Day 0 = the day of AI). Pregnancy was confirmed using brightness-mode ultrasonography on Day 30. In pregnant group (n = 141), CL area and CL tissue area were greater (P < 0.001) than those in non-pregnant group (n = 89) on and after Day 19. Moreover, BFA was greater (P < 0.05) in pregnant group on and after Day 18. The overall central cavity incidence was lower (P < 0.001) and CCA was smaller (P < 0.001) in pregnant group. Logistic regression analyses revealed that the best single predictor for pregnancy diagnosis was BFA on Days 17-20 (sensitivity = 69%-100% and specificity = 65%-91%). On Day 21, CL area or CL tissue area was the most accurate predictor (cutoff value = 267.78 mm, sensitivity = 100%, and specificity = 100%). The best set of predictors for pregnancy diagnosis was specified as the BFA and [CCA × BFA] pair. Setting BFA cutoff value in the cattle without central cavity at 55.26 mm yielded the highest sensitivity (97%) and specificity (88%) on Days 18-20. The accuracy of pregnancy diagnosis using BFA or BFA and [CCA × BFA] pair on Day 17 was lower than those on and after Day 18. In conclusion, BFA and CCA are effective for early pregnancy diagnosis on Days 18-20 post-AI in JB cattle; however, it is inadequate on Day 17 owing to its low accuracy. Evaluating CL area or CL tissue area on Day 21 is the most accurate method of pregnancy diagnosis.