Effect of interval between OPU sessions on the efficiency of oocyte retrieval at intensive using of donors of different cattle breeds

The article presents data on the efficiency of transvaginal ultrasound-guided oocyte retrieval (OPU) depending on the interval between sessions at intensive use of donors in cattle of various breeds. Donors of Kholmogory (n = 7), Istoben (n = 7) and Tagil (n = 4) cattle breeds were used in the experiment. Four OPU sessions were performed on each of the donors with each of two different intervals: 4 days and 3 days. The greatest number of follicles was found in heifers of the Kholmogor breed (13.23 ± 0.51 follicles versus 9.09 ± 0.44 and 9.38 ± 0.61 follicles, respectively, in heifers of the Istoben and first-lactation cows of Tagil breeds), while the interval between sessions did not significantly affect this indicator. In the first-lactation cows of the Tagil breed, a greatest number of cumulus-oocyte complexes (COCs) was obtained when using the interval between sessions of 3 days compared to 4 days — 5.69 ± 0.64 versus 4.06 ± 0.59 COCs (p < 0.05). There were no significant differences in the donors of the Kholmogor and Istoben breeds — 8.32 ± 0.75 versus 7.82 ± 0.59 COCs and 3.82 ± 0.40 versus 3.52 ± 0.57 COCs, respectively. The interval between sessions did not have a noticeable effect on the quality of the retrieved COCs. Thus, the absence of significant effect of different interval between OPU sessions on the number of obtained COCs, which are suitable for in vitro embryo production in all three studied breeds was shown (5.75 ± 0.54 vs 6.43 ± 0.66, 2.55 ± 0.45 vs 2.79 ± 0.48 and 2.88 ± 0.53 vs 4.00 ± 0.50 in donors of the Kholmogor, Istoben and Tagil breeds, respectively). This allows us to recommend conducting OPU sessions with alternating intervals of 4 days and 3 days for oocyte retrieval at intensive using of donors of above mentioned cattle breeds.