Luteinizing hormone secretion, ovulatory capacity, and oocyte quality in peripubertal Gir heifers

Abstract

SummaryInduction of puberty in cattle breeds that attain puberty in later stages, such as Gir, allows the earlier beginning of reproductive life and it might increase oocyte quality. Here, the ovulatory capacity of prepuberal Gir heifers was studied and its relationship to follicular growth, luteinizing hormone (LH) secretion and oocyte quality was evaluated. Peripubertal Gir heifers were treated with a progesterone-based protocol and according to ovulatory response were separated into groups: not-ovulated (N-OV) and ovulated (OV). Serial blood samples were taken 24 h after estradiol treatment on day 12 to evaluate LH secretion. Cumulus–oocyte complexes (COCs) were collected using ovum pick-up and assessed for brilliant cresyl blue (BCB) staining rate, IVF-grade oocytes rate, and mean oocyte diameter, in comparison with cow oocytes. Gene expression of developmental competence markers (ZAR1, MATER, and IGF2R) was also analyzed. The largest follicle diameters were similar between N-OV and OV groups on the day of estradiol treatment (d12) and the next day and decreased (P = 0.04) in the N-OV group thereafter. LH pulse secretion was different between groups (N-OV = 3.61 ± 0.34 vs OV = 2.83 ± 0.21 ng/ ml; P = 0.04). COC assessment showed that the number of recovered oocytes, BCB+ rate, IVF-grade oocytes and oocyte size was similar (P > 0.05) among groups, resembling adult cow patterns. ZAR1, MATER and IGF2R gene expression in oocytes were also similar (P > 0.05) in N-OV and OV groups. In conclusion, our results demonstrate a lower LH secretion profile in peripubertal Gir heifers prone to ovulate after induction protocol, and that oocyte quality is not affected on a short-term basis by ovulation itself.