Using Color Flow Doppler Ultrasonography to Estimate Progesterone Concentrations at Embryo Transfer and During Early Pregnancy in Recipient Mares

Color-flow Doppler sonography (CF) has been described as a means of rapidly assessing corpus luteum (CL) function in cycling mares because luteal blood flow correlates with circulating progesterone (P4) concentrations. The hypothesis was that CL size and blood flow would provide an indication of luteal function as represented by circulating levels of P4, in mares at and following embryo transfer (ET). Day 8 equine embryos (n=48) were transferred into available recipient mares (ovulated 1 day before to 3 days after donor) as part of a commercial program. B-mode and CF sonography were performed using a MyLabTMFive (Esaote, Maastricht, The Netherlands) immediately prior to ET (ET+0), and blood was collected from the jugular vein to measure plasma [P4] (Coat-A-Count TKPG; Siemens Healthcare Diagnostic BV, Los Angeles, CA). [...]