Breed composition does not influence the performance of Holstein-Gyr crossbred as oocyte donors for OPU/IVP

Holstein-Gyr crossbred cattle are strategic for dairy systems in tropical countries, since they combine milk yield genetics with adaptability to tropical climate. However, Holstein (Bos taurus) and Gyr (Bos indicus) breeds present remarkable differences regarding reproductive physiology. Brazil stands out as the world's largest user of embryo in vitro production (IVP) in bovine, and the use of this technique is increasing in dairy systems. As Holstein-Gyr crossbreds are important oocyte donors for IVP, the present work aimed at investigating whether increased Gyr or Holstein breed composition influences donor's performance. Sixteen Holstein-Gyr crossbred females presenting increased (HG, 71.4 to 87.5% Holstein; n = 9) or decreased (GH, 40.2 to 46.6% Holstein; n = 7) Holstein composition were submitted to three ovum pick up (OPU) sessions. We observed similar (P = 0.2946) antral follicle count between HG and GH donors (24.8 +/- 3.2 vs 29.4 +/- 2.8 respectively; mean +/- SEM). Groups also display similar morphological oocyte grading (Grade I: 0.1 +/- 0.1 vs 0.1 +/- 0.1 - P = 0.9680; Grade II: 0.9 +/- 0.5 vs 1.9 +/- 0.5 - P = 0.1942; Grade III, 4.0 +/- 1.2 vs 7.2 +/- 1.4 - P = 0.1047, HG vs GH respectively; mean +/- SEM). Additionally, the proportion of viable oocyte was similar between HG and GH groups (27.8% vs 31.9%, respectively, P = 0.3500) and oocyte lipid area fraction (6.8% vs 9.5%, respectively; P = 0.1539). Our results indicate that the individual variation has more influence than breed composition of crossbred oocyte donors.