Testicular heat stress affects sperm quality and fertility. However, the chronology of these effects is not yet fully understood. This study aimed to establish the early sequential effects of heat stress in bull sperm quality. Semen and blood samples of Nellore breed bulls were collected and distributed into control and testicular heat stress (scrotal bags/96 h) groups. Semen samples were evaluated for sperm motility, abnormalities, plasma membrane integrity, acrosomal membrane integrity, mitochondrial membrane potential, sperm lipid peroxidation, seminal plasma lipid peroxidation, and DNA fragmentation. Blood plasma was also evaluated for lipid peroxidation. An increase in sperm abnormalities was observed 7 days following heat stress. After 14 days, sperm lipid peroxidation increased and mitochondrial membrane function, sperm motility, and plasma membrane integrity decreased. Heat stress effects were still observed after 21 days following heat stress. An increase in sperm DNA fragmentation was observed as a late effect after 28 days. Thus, the initial effects of heat stress (i.e., increasing sperm abnormalities and lipid peroxidation) suggest the presence of oxidative stress in the semen that alters mitochondrial function, sperm motility, plasma membrane integrity, and belatedly, DNA fragmentation. Although sperm abnormalities persisted and increased over time, sperm lipid peroxidation, in turn, increased only until 21 days after heat stress. In this regard, these findings provide a greater understanding of the chronological effects of experimentally induced heat stress on bovine sperm, providing valuable insights about spermatogenesis during the first 28 days following heat stress.

中文翻译：

---

热应激对牛精子细胞的影响：早期发现的时间顺序方法

睾丸热应激会影响精子质量和生育能力。然而，这些影响的时间顺序尚未完全了解。本研究旨在确定热应激对公牛精子质量的早期连续影响。收集 Nellore 品种公牛的精液和血液样本并将其分配到对照组和睾丸热应激（阴囊袋/96 小时）组。评估精液样本的精子活力、异常、质膜完整性、顶体膜完整性、线粒体膜电位、精子脂质过氧化、精浆脂质过氧化和 DNA 断裂。还评估了血浆的脂质过氧化。热应激后 7 天观察到精子异常增加。14 天后，精子脂质过氧化增加，线粒体膜功能、精子活力、和质膜完整性降低。热应激后 21 天后仍观察到热应激效应。在 28 天后观察到精子 DNA 断裂的增加作为晚期效应。因此，热应激的初始影响（即增加精子异常和脂质过氧化）表明精液中存在氧化应激，该氧化应激会改变线粒体功能、精子活力、质膜完整性，以及迟来的 DNA 断裂。尽管精子异常持续存在并随着时间的推移而增加，但精子脂质过氧化仅在热应激后 21 天才会增加。在这方面，这些发现提供了对实验诱导的热应激对牛精子的时间顺序影响的更深入的了解，