Prepubertal heifers versus cows-The differences in the follicular environment

Area of Science:

• Reproductive Biology
• Animal Science
• Oocyte Biology

Background:

• Oocyte quality is significantly influenced by the sexual maturity of the donor female, a phenomenon well-documented in domestic animals but with poorly understood underlying mechanisms.
• Existing research often focuses on oocyte ultrastructure, fertilization issues, and blastocyst development rates, leaving the follicular environment's role less explored.

Purpose of the Study:

• To characterize and compare the follicular environment, including oocytes, cumulus cells (CC), granulosa cells (GC), and follicular fluid (FF), between prepubertal heifers and mature cows.
• To investigate differences in lipid droplet (LD) content in oocytes, gene expression related to energy metabolism in CC and GC, and the biochemical composition of FF.

Main Methods:

• Collected ovarian follicles from prepubertal heifers and cows for comparative analysis.
• Quantified lipid droplet (LD) number in oocytes and analyzed the expression of seven energy metabolism-related genes (ELOVL2, ELOVL5, SCD, FADS2, GLUT1, GLUT3, GLUT8) in CC and GC.
• Assessed fatty acid (FA) composition and glucose concentration in the follicular fluid (FF).

Main Results:

• Cow oocytes were larger and contained more LDs than heifer oocytes, both before and after in vitro maturation (IVM).
• Follicular fluid from cows showed higher glucose and fatty acid concentrations compared to heifers.
• Significant differences in gene expression (ELOVL, FADS2, SCD, GLUT3, GLUT8) were observed in CC and GC between heifers and cows, with SCD mRNA being more abundant in cow GC.

Conclusions:

• Distinct follicular environments in heifers and cows contribute to differences in oocyte quality.
• The suboptimal environment in heifer follicles (lower glucose and FA in FF) may lead to reduced oocyte quality and maturation potential.
• Superior oocyte quality in cows, evidenced by higher LD number and diameter, suggests better developmental potential for future embryos.