Dynamics of the Reproductive Changes and Acquisition of Oocyte Competence in Nelore (Bos taurus indicus) Calves during the Early and Intermediate Prepubertal Periods

Abstract

The purpose of this study was to characterize the reproductive physiology, oocyte competence, and chromatin compaction in Nelore calves in the early-prepubertal period (EPP) and the intermediate-prepubertal period (IPP). Calves aged 2–5 (EPP) and 8–11 months old (IPP) were assigned to Trial 1 (morpho-physiological–endocrine evaluations, n = 8) or Trial 2 (oocyte donors, n = 8) vs. the respective control groups of cows (n = 8, each). All morphological endpoints, except the antral follicle count, increased from the EPP to the IPP. The EPP LH-FSH plasma concentrations were similar to cows, whereas LH was lower and FSH was higher in the IPP than in cows. . Cows produced more Grade I (12.9% vs. 4.1% and 1.7%) and fewer Grade III COC (30.1% vs. 44.5% and 49.0%) than the EPP and IPP calves, respectively. The IPP calves’ oocyte diameter was similar to those from cows but greater than those from EPP females (124.8 ± 8.5 and 126.0 ± 7.5 μm vs. 121.3 ± 7.5 μm, respectively). The expression of the chromatin compaction-related gene HDAC3 was downregulated in calves. The proportion of the blastocyst rate to the controls was lower in EPP than in IPP calves (43.7% vs. 78.7%, respectively). Progressive oocyte competence was found during the prepubertal period, which can help to decide whether to recover oocytes from calves.

Female Bovine Donor Age Influence on Quality Markers’ Expression and PPARS Abundance in Day 7 Blastocysts

“…The production of embryos in vitro (IVEP) in combination with oocyte collection by transvaginal ovum pick up (OPU) is becoming a more popular method of livestock production, especially in the bovine industry (Galli et al, 2014). The latest molecular innovations, such as genomic predicted transmitting ability (GPTA) or genomic selection of embryos (GS), alongside the continuous search for production (Jiang et al, 2019;Kawamoto et al, 2022) or wellness (McNeel et al, 2017) genetic traits in cattle, allow those involved to evaluate animals at the very early stage of life (Jiang et al, 2019;Ferré et al, 2021). Hence, the use of OPU-IVEP followed by molecular evaluation of the produced embryo may help to breed only the most valuable animals.…”