Ultrasonic Evaluation of the Corpus Luteum in Alpacas With Embryo Removal on Day 9 Post-Mating

The objective of the present study was to determine the diameter, area, circumference, and blood flow of the corpus luteum (CL) using transrectal ultrasonography in female alpacas with and without the presence of an embryo on Day 9 post-mating, the time of maternal recognition of pregnancy (MRP). For this purpose, 12 female alpacas with follicles ≥ 7 mm were mated with fertile males and treated with 0.0084 mg of buserelin acetate (Day 0). After that, the females were randomly classified into 2 groups (6 animals/group): (1) CL with embryo and (2) CL without embryo (embryo removed from the uterine horn on Day 9). In both groups, transrectal ultrasonography was performed on Day 2 to determine ovulation, and on Days 5, 7, 9, 11, and 13 to evaluate the CL. The data were analysed using repeated measures ANOVA. The diameter (mm), total area (mm²), circumference (mm), and blood flow (%) of the CL were significantly decreased in the CL without embryo group on Days 11 and 13 (6.9 ± 0.6 and 2.9 ± 1.1, 48.3 ± 5.6 and 12.3 ± 4.7, 22.4 ± 1.9 and 7.4 ± 2.5 and 39% and 55%, respectively) compared to the CL with embryo group (12.1 ± 0.9 and 12.1 ± 0.6, 111.1 ± 17.1 and 107.5 ± 8.8, 37.2 ± 2.8 and 37.0 ± 1.7, and 3% and 3%, respectively). In conclusion, the CL characteristics in alpacas with embryo removal changed drastically after Day 9, presenting progressive regression in size and blood flow from Day 11 to 13. These results might indicate that the presence of an embryo on Day 9 is necessary to trigger the signal that prevents luteolysis in this species.