EC Clinical and Medical Case Reports

Introduction: Insulin-like growth factors (IGF-I and IGF-II) are crucial for cell division, blastocyst formation, implantation, and overall embryo growth. These growth factors function through endocrine, paracrine, and autocrine mechanisms. The expression of IGF-1 and IGF-2 mRNA has been studied in bovine, buffalo and sheep embryos, but there remains limited understanding of how seasonality influences the expression of these genes in pre-implantation sheep embryos.

Objective: This study aims to investigate the impact of seasonal variations on cleavage rates, embryo development, and the expression of IGF-1 and IGF-2 mRNA in sheep embryos.

Methods: Ovaries with follicles ranging from 2 to 6 mm were aspirated during three different breeding seasons: summer (March to April), autumn (June to July), and post-monsoon (September to October). Oocytes with more than 5 layers of cumulus cells and homogeneous granular ooplasm were cultured in maturation medium at 38.5°C with 5% CO₂ for 22 - 24 hours. These in vitro matured oocytes were fertilized with fresh semen, and fertilization, cleavage, and blastocyst development were monitored.

Results: During summer, autumn, and post-monsoon seasons, cleavage rates were 54.63 ± 2.55%, 67.67 ± 2.33%, and 68.97 ± 1.76%, respectively, with significant (P < 0.05) difference observed between summer and post-monsoon seasons. The blastocyst development was significantly (P < 0.05) higher during post-monsoon season compared to summer. The expression of IGF-1 and IGF-2 mRNAs was significantly (P < 0.05) elevated in the blastocyst stage during the post-monsoon season in comparison to both the summer and autumn seasons, across all stages of embryo development (immature, mature, 8-cell, 16-cell, morula, and blastocyst).

Conclusion: Summer season was associated with a lower cleavage rate and poorer blastocyst development compared to the autumn and post-monsoon seasons.

 Keywords: Oocytes; Sheep; Season; In vitro Maturation; Cleavage Rate; IGF-1 and IGF-2

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