Effect of transvaginal oocyte aspiration on progesterone concentrations and estrous cycle length in domestic jennies

With the growing interest in developing assisted reproductive techniques for breeding or animal preservation purposes, transvaginal oocyte aspiration or ovum pick up (OPU) has become an established technique for collecting oocytes and in vitro embryo production in the horse. However, no studies have explored the impact of OPU on the estrous cycle and progesterone dynamics in jennies. Our work aimed to investigate the effect of the OPU procedure on estrous cycle length and plasma progesterone concentration in jennies. Ten healthy Argentinian native domestic jennies aged 3 to 12 years were used for this experiment. A total of 18 estrous cycles were evaluated during one breeding season: eleven control and seven cycles with OPU. Jennies were monitored every second day by ultrasonography until ovulation was detected (ovulation day = day 0 of the estrous cycle). Blood samples for progesterone determination were obtained from two control and three OPU cycles every two days for an entire estrous cycle (control) and from OPU day until the following ovulation (OPU group). Progesterone concentration was measured by Chemiluminescent Microparticle Immunoassay. For the OPU procedure, jennies on days 8 and 12 of the estrous cycle with more than six total follicles and no follicles larger than 25 mm were selected. The OPU procedure was performed as described by Bragulat et al. (Theriogenology. 2023; 195:199-208). Student's t-test was used to compare estrouscycle length, and analysis of variance (ANOVA) was conducted to determine whether there were any statistically significant differences in progesterone concentrations between control and OPU groups. The estrous cycle length of jennies subjected to OPU was significantly longer (P=0.02) than the control group (mean ± SEM, minimum / maximum values): Control, 22.64 ± 0.85 16/27 days; OPU, 26,00 ± 0.93 23/28 days. No luteinized structures were found after OPU sessions. In control estrous cycles, progesterone concentration increased after ovulation, reaching a peak on day 12 (mean ± SEM values; 36.20 ± 0.99 ng/ml) and decreasing to baseline concentration from day 16 (4.65 ± 3.18 ng/ml) to day 20 (0.75 ± 0.21 ng/ml). The results showed a significant difference in progesterone concentrations between the control and OPU groups (p = 0.003). Specifically, jennies subjected to OPU had lower progesterone concentrations from day 10 to 14 compared to the control group. Interestingly, both groups reached a similar baseline by day 16 unt