111 Effect of dominant follicle size on the form and function of the corpus luteum in alpacas (Vicugna pacos)

Genetic improvement in alpacas is difficult owing to challenges to their reproductive physiology (i.e. long gestation time and delayed puberty). Assisted reproductive technologies (ART), such as embryo transfer can be used to permit alpaca’s improvement; however, high embryo mortality (EM) affects the success of these technologies in alpacas. A higher percentage of EM occurs because of failure in the establishment of the corpus luteum (CL) or a deficiency in progesterone (P4) secretion. Improving the form and function of the CL and P4 secretions could decrease EM and increase the success of ART in this species. In other species (e.g. cattle), greater CL and higher levels of P4 were obtained when a large preovulatory follicle ovulated. Therefore, the objective of this study was to determine the effect of the dominant follicle (DF) size on the CL diameter and blood flow (BF) and the plasma P4 levels at Day 7 after induction of ovulation in alpacas. Day 7 is the day for embryo transfer into alpaca recipients. For this purpose, 24 female alpacas with ≥7-mm DFs were selected and divided into two groups (n = 12 per group): (1) DF 7–8 mm (females with DF of 7 to 8 mm on the day of mating) and (2) DF 9–10 mm (females with DF of 9 to 10 mm on the day of mating). Females were mated and received a single i.m. dose of 0.0084 mg of buserelin acetate (Day 0). Ovulation was verified by transrectal ultrasound on Day 2 in both groups. On Day 7, the characteristics of the resulting CL were evaluated by transrectal ultrasonography. The diameter (mm) of the CL was determined by B-mode ultrasound, and the BF, measured as the percentage of CL tissue showing color signals, was determined using color Doppler ultrasound. Blood samples were taken on Day 7 to measure plasma P4 concentrations in both groups. The data were analyzed using the student t-test and the Chi-squared test. The diameter of the CL was greater (P < 0.05) in the DF 9–10 mm group (11.4 ± 0.4 mm) than in the DF 7–8 mm group (10.3 ± 0.2 mm). The percentage of CL blood flow was not different between groups (29% in the DF 9–10 mm group and 25% in the DF 7–8 mm group). However, P4 levels were significantly higher (P < 0.05) in the DF 9–10 mm group (5.81 ± 0.4 ng mL⁻¹) than in the DF 7–8 mm group (4.36 ± 0.3 ng mL⁻¹). In conclusion, inducing ovulation in dominant follicles of 9–10 mm resulted in a larger CL that produced higher P4 levels on Day 7 postmating in alpacas. This information can be used in the preparation of recipients for an embryo transfer program in alpacas.

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