110 Corpus luteum characterization after embryo removal using the B mode and color Doppler ultrasound in alpaca (Vicugna pacos)

Embryo mortality is one of the most important factors that affects alpaca production. Importantly, a higher percentage of embryo mortality occurs around Day 9, which is the time of the maternal recognition of pregnancy (MRP) in alpacas. However, tests that allow determining whether or not an embryo is present in the uterus at Day 9 are not available. Evaluating the alpaca corpus luteum (CL) by ultrasonography is an approach that could help to determine pregnancy. Alpacas with a viable embryo are expected to have a functional CL by and after Day 9. When the embryo is not present or not viable, the MRP will not be triggered, and the CL will regress. Therefore, the objective of this study was to identify the main characteristics of the CL by ultrasonography from Day 9 to Day 13 of pregnancy in alpacas with and without an embryo present in the uterus. Twelve nonpregnant alpacas (aged 3–4 years and average body condition score of 3 out of 5) with 7-mm follicles were mated, treated with 0.0084 mg of buserelin acetate, and randomly allocated into two groups (six animals per group): (1) CL with embryo, and (2) CL without embryo (the embryo was removed by nonsurgical transcervical technique on Day 9 to prevent it from giving the signal for the MRP to avoid luteolysis). In both groups, transrectal ultrasonography was performed on Day 2 to determine ovulation (only ovulated females continued in the study) and on Days 9, 11, and 13 to evaluate the characteristics of the CL. The CL diameter (D) in millimeters and the total CL area (TA) in squared millimeters were determined by B mode ultrasonography, and the percentage of CL blood flow (BF) was evaluated using color Doppler ultrasound. The data were analyzed using repeated measures ANOVA. Proportions were previously transformed using arcsin square root transformation. In the group CL without embryo, D, TA, and BF of the CL decreased significantly toward Day 13, whereas in the group CL with embryo, these parameters remained unchanged or increased (Table 1). In conclusion, the morphological characteristics of CL in alpacas with embryo removal were different from those in alpacas with an embryo in uterus where it was observed a progressive CL regression after Day 9. The CL characteristics from Day 11 to 13 could be used as an early indication of nonpregnancy in alpacas. Additionally, these results indicate that the presence of the embryo from Day 9 is a key factor in the MRP signal for preventing luteolysis in alpacas.

Research was funded by PROCIENCIA-CONCYTEC, Peru (project code PE501082272-2023).