Doctoral Thesis
Breed-specific responses to mild scrotal heat stress: effects on spermatogenic cells, endocrine function, signalling pathways and semen quality in Wugu-Hu and Hu rams
Murdoch University
Doctor of Philosophy (PhD), Murdoch University
2025
DOI:
https://doi.org/10.60867/00000042
Abstract
Heat stress is a major environmental factor affecting ram fertility. Genetic differences between sheep breeds are associated with their varying levels of heat stress tolerance. To explore the breed specific responses to thermal challenge in ram spermatogenesis, this study comprehensively evaluated semen quality, testicular transcriptome, and testicular cellular alterations in Hu and Wugu-Hu crossbred rams following 72 hours of mild scrotal heat stress.
In semen quality analysis, utilising a controlled experimental design, we subjected twelve adult rams (six purebred Hu and six Hu × Wugu crossbred) to scrotal insulation to simulate mild heat stress conditions. Semen samples were collected every five days from day 11 to day 56 after the end of scrotal insulation. The results demonstrate that scrotal insulation led to a continuous and stable increase in scrotal surface temperature (3.0±0.1 °C) without significantly affecting testicular circumference (p > 0.05). Compared to the control group, both breeds exhibited a temporary reduction in sperm motility from day 11 to day 21 and increased sperm morphological defects from day 11 to day 46 (p < 0.05). The morphologic defects consisted of head defects (day 11 and day 41), tail defects (day 11 and days 31-41), and midpiece defects (days 11-41) in the 56-day collection period. No significant differences in the recovery trends of sperm quality were observed between the two breeds, but the decrease in semen quality on day 41 only occurred in Wugu-Hu ram and was not observed in Hu ram (p < 0.05).
Additionally, testicular samples from twelve adult rams (three Hu rams without scrotal insulation, three Hu rams with scrotal insulation, three Wugu-Hu rams without scrotal insulation, and three Wugu-Hu rams with scrotal insulation) were used for transcriptomic analysis and testicular cellular analysis. Differentially expressed genes in Wugu–Hu rams were significantly enriched in pathways related to meiosis, cell cycle, and signalling, including downregulating key regulators such as CDK1, CDC20, and PLK1. However, the transcriptomic changes in Hu sheep were more stable, with the differentially expressed genes after heat stress showing no significant enrichment in pathways or biological functions.
Immunohistochemical staining further confirmed increased germ cell apoptosis and reduced spermatogenic activity in Wugu-Hu sheep testis, especially in spermatogonia and early spermatocytes. Wugu-Hu rams demonstrated accumulation of spermatocytes in the zygotene stage, which were not observed in Hu sheep, indicating scrotal heat stress disrupted the meiotic progression in Wugu-Hu rams. These findings prove that Wugu-Hu rams showed lower thermotolerance at both cellular and molecular levels than Hu rams.
This study shows the importance of genetic background in determining reproductive resilience under heat stress. It further contributes novel insights into the mechanisms of thermosensitivity in Wugu-Hu sheep and may inform future strategies for genetic selection and thermal stress mitigation in sheep breeding programs.
Details
- Title
- Breed-specific responses to mild scrotal heat stress: effects on spermatogenic cells, endocrine function, signalling pathways and semen quality in Wugu-Hu and Hu rams
- Authors/Creators
- Shikun Chen
- Contributors
- Pete Irons (Supervisor) - Murdoch University, School of Veterinary MedicineHuansheng Dong (Supervisor) - Qingdao Agricultural UniversityHenry Annandale (Supervisor) - Murdoch University, School of Veterinary MedicineQingjie Pan (Supervisor) - Qingdao Agricultural University
- Awarding Institution
- Murdoch University; Doctor of Philosophy (PhD)
- Publisher
- Murdoch University
- Identifiers
- 991005845964307891
- Murdoch Affiliation
- School of Veterinary Medicine
- Resource Type
- Doctoral Thesis
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