The size of the dominant follicle influences the morphological and functional characteristics of the corpus luteum in alpacas (Vicugna pacos)

The objective of this study was to determine the effect of the dominant follicle (DF) size on the corpus luteum (CL) characteristics and plasma P₄ concentrations, 7 days after induction of ovulation in alpacas. For this purpose, 24 female alpacas were selected and divided into 2 groups (n = 12/group): i) DF 7–8 mm (females with DF of 7–8 mm on the day of mating) and ii) DF 9–10 mm (females with DF of 9–10 mm on same day). Females received a single i.m. dose of 0.0084 mg of buserelin acetate on the day of mating (Day 0). On day 7, the diameter (mm), total area (mm²), circumference (mm), and blood flow (%) of the CL were evaluated by transrectal ultrasonography. Blood samples were taken on day 7 to measure plasma P₄ concentrations in both groups. The data was analyzed using the T-student and Chi-square test. The diameter, total area, and circumference of the CL were greater (P < 0.05) in the DF 9–10 mm group than in the DF 7–8 mm group. However, the percentage of blood flow in CL was not different between groups. Interestingly, P₄ concentrations were higher (P < 0.05) in the DF 9–10 mm group (5.81 ± 0.4 ng/mL) than in the DF 7–8 mm group (4.36 ± 0.3 ng/mL). In conclusion, inducing ovulation in dominant follicles of 9–10 mm resulted in a larger CL that produced higher P₄ concentrations on day 7 post-mating in alpacas. This information can be used in the preparation of recipients for an embryo transfer program in alpacas.