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

Abstract

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 mm2, 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 mm2 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.