The value of evaluating luteal blood flow on the day of embryo transfer for recipient selection in Holstein lactating dairy cows

Recipient selection based on corpus luteum (CL) function is important for the success of embryo transfer (ET) in cattle. In this study, we evaluated the value of the parameters of luteal blood flow on the day of ET as a means of recipient selection in Holstein lactating dairy cows. The parameters of luteal blood flow [blood flow area (BFA) and blood perfusion (BP)], and CL size [luteal diameter, luteal area and luteal tissue area] and peripheral plasma progesterone (P-4) concentrations were evaluated at immediately before ET (n = 25) then cows were transferred embryos. The area under the ROC curve (AUC) showed that BFA and BP were effective to predict pregnancy and their AUCs (AUC > 0.70) were similar (P > 0.1). Pregnancy rates of high BFA (BFA >= 0.93 cm(2), n = 9) or BP (BP >= 26.0%, n = 12) groups was higher than that of low groups (BFA: 66.7% vs. 12.5%, BP: 50.0% vs. 15.4%). There was no correlation between plasma P-4 concentrations and luteal blood flow. The proportions of cows classified high group were different between cows with a large CL (luteal diameter >= 2.0 cm, n = 15) and those with a small CL (n = 10) in BFA (53.3% vs. 10.0%, P < 0.05) while similar between them in BP (46.7% vs. 50.0%). In conclusion, although BFA and BP are independent on the peripheral plasma P-4 concentration, they serve as indicators of fertility. The accuracy of predicting pregnancy might be similar, but the characteristic of recipient selection may be different between the two indicators.