Optimizing embryo transfer management in cows: Ultrasound-based pre-transfer screening and management of non-eligible...

A single pre-transfer ultrasound screening cannot capture dynamic changes from estrus to ovulation. This may leads to inaccurate recipient selection and undetected reproductive abnormalities in non-eligible cows. We established a dynamic ultrasound monitoring (DUM) protocol with examinations on estrus day D0 (estrus detection), D1 (ovulation confirmation), and D6 (morphological assessment of the corpus luteum [CL]), and provided stage-specific management for non-eligible recipients. A total of 2,329 cows were randomly assigned to a control group (n = 1,165; a single ultrasonographic evaluation at the time of embryo transfer [ET]) or DUM group (n = 1,164). Before ET, first-service cows received a Presynch11/Ovsynch protocol, whereas second- and third-service cows were either observed for estrus or treated with an Ovsynch protocol based on whether or not they were observed in estrus up to pregnancy diagnosis of the previous breeding. In the control group, all non-eligible cows uniformly received Ovsynch + timed artificial insemination (AI). In the DUM group, non-eligible cows received stage-specific treatments based on ultrasound findings. In both groups, non-eligible cows were subsequently bred only via AI. The DUM group had a higher proportion of reconfirmed pregnancies per ET (43.2% vs. 37.4%). Among DUM cows, larger follicle diameter on D0 increased the proportion of reconfirmed pregnancies per ET (OR = 1.504), while severe bleeding at transfer reduced it (OR = 0.464). The non-eligible rates were similar between groups (28.9% in the control group and 28.2% in the DUM group). In the control group, the reasons for non-eligibility were predominantly absent CL (70.9%) or poor CL quality (17.2%), based on the single D7 evaluation. In the DUM group, the reasons were distributed across time points: 31.6% on D0 (presence of a large CL), and on D6, 26.7% due to no CL and 23.4% due to poor CL quality. Among non-eligible cows, the DUM group had a higher proportion of pregnancies per subsequent AI (42.9% vs. 28.5%), fewer services per pregnancy (2.53 vs. 2.82) and shorter days open (130.10 vs. 135.88). The cost per successful pregnancy in eligible recipients was $78.69 lower in the DUM group than in the control group. In conclusion, the DUM protocol improves both ET success and subsequent fertility of non-eligible recipients, offering an efficient management strategy for dairy herds.