PSXVI-16 - The quality of cows’ oocyte derived at different timing regimens of transvaginal follicular puncture

Recovery of oocytes from live animals through ultrasound-guided transvaginal follicular aspiration (Ovum Pick-Up, OPU) is an essential element of modern livestock development. The aim of our work was to study the effect of two different timing regimens on the quality of oocytes, recovered from cycled Simmental heifers (n = 4). Follicle aspirations were performed once a week (1/w) or twice a week (2/w). The same donor animals were used for each timing regimens. 228 and 224 follicles were aspirated at 2/w and 1/w regimen, respectively, and 280 cumulus-oocyte complexes (COCs) were recovered (140 COCs at each of timing regimen), which corresponds to the recovery rate of 61.4±5.9% and 62.1±6.3%. On average, 4.4 oocytes were received from each donor per session. We observed a significant increase by 1.2 times (P < 0.05) of the proportion of OPU-oocytes of good quality, which were characterized by normal morphology, when performing the procedure in the 2/w compared to 1/w regimen (65.7±4.0% vs. 53.6±3.0% of the total number of recovered oocytes, respectively). The proportion of oocytes at the MII stage of meiosis after 24 hours of maturation was similar in both groups: 73.3±5.6% (2/w regimen) and 74.7±2.4% (1/w regimen). Proportion of oocytes with signs of apoptotic changes was also not significantly differed between the groups: 8.0±3.1 and 9.8±3.3%, respectively. We did not observe the effect of the frequency of OPU sessions on the embryo cleavage rate (on average 63.5%) and the blastocysts development rate (on average 16.7%). Our data will be used to optimize the timing regimen of oocyte retrieval from living Simmental donor heifers. The studies were performed under financial support of the RFBR (project No. 20-316-90003) and the Russian Ministry of Science and Higher Education.