Association between Ovum Pick-Up (OPU) frequency and stressrelated hormone concentrations in Holstein heifer oocyte donors

Purpose : to determine whether transvaginal ultrasound-guided ovum pick-up (OPU) procedures influence the concentrations of stress-associated hormones in the serum of Holstein heifer oocyte donors, and to assess whether the intensity and duration of donor use affect these hormonal indicators. Materials and Methods . The study was conducted at the L. K. Ernst Federal Research Center for Animal Husbandry (FGBNU FIC VIZh) on Holstein heifers (n = 10) with synchronized estrous cycles. Four days after the onset of estrus, transvaginal ultrasound-guided follicular aspiration was performed. Five animals (regimen 1w) underwent OPU once per week at 7-day intervals, while another five animals (regimen 2w) were subjected to OPU twice per week at 3—4-day intervals. The total number of procedures was 10 for regimen 1w and 20 for regimen 2w, each divided into two equal-duration periods. Blood samples were collected the day after estrus onset and on each OPU day. Serum concentrations of cortisol, adrenaline, and noradrenaline were determined using enzyme- linked immunosorbent assay (ELISA). Results . Following the first OPU session, serum concentrations of stress-related hormones in donors increased significantly. Cortisol levels rose from 15,8 [4,8; 36,2] ng/mL before OPU to 26,8 [15,5; 49,0] ng/mL after the first aspiration (p = 0,0195); adrenaline increased from 60,3 [44,8; 108,1] to 105,0 [69,2; 132,6] pg/mL (p = 0,0488); noradrenaline from 51,0 [43,7; 53,9] to 70,7 [54,8; 82,5] pg/mL (p = 0,0137), respectively. No significant differences in hormone concentrations were observed between regimens 1w and 2w when compared within identical periods (p>0,05). Cortisol levels remained comparable across the studied time points (p>0,05). In both regimens, adrenaline and noradrenaline concentrations were higher during OPU sessions than outside OPU periods. In the twice-weekly regimen (2w), the concentrations of the analyzed hormones in the second period (OPU11—20) were significantly higher than in the first (OPU1—10) (p0,05). These findings are preliminary, as comprehensive evaluation of the technology’s efficiency requires consideration of reproductive outcomes in light of the obtained data.