The aim of this study was to assess seasonal variations during different periods of the breeding season (spring and summer) on stallion sperm DNA fragmentation and in vivo fertility associated with cooled-stored semen samples. Ejaculates were collected from eleven stallions and assessed for sperm motility (assessed by computer-assisted sperm analysis) and plasma membrane integrity (evaluated under fluorescence microscopy). Sperm DNA fragmentation (evaluated by the Sperm Chromatin Dispersion test) was assessed in cooled-stored semen at 5 °C for up to 24 h. Artificial insemination was performed throughout the breeding season. Mares were inseminated with cooled-stored semen (up to 24 h) every other day until ovulation. Pregnancy rates per cycle were determined detecting the embryonic vesicle by ultrasonography fifteen days after ovulation. Values (mean ± SD) for progressive sperm motility were significantly higher (P < 0.05) in spring (53.57 ± 9.97%) in comparison to summer (41.37 ± 10.81%). No significant differences in plasma membrane integrity were found between seasons (P > 0.05). Sperm DNA fragmentation was significantly lower (P < 0.01) in spring in comparison to summer after 0h (4.81 ± 1.87% vs. 8.77 ± 5.78%), 6h (9.00 ± 3.19% vs. 18.73 ± 8.22%) and 24h (14.6 ± 4.13% vs. 30.14 ± 9.85%) of cooled-storage. Pregnancy rates per cycle were also significantly higher (P < 0.01) in spring (50%) in comparison to summer (37%). There was a moderate negative relationship between positive pregnancies and sperm with fragmented DNA (r = - 0.619; P < 0.001). Semen samples associated with moderate fertility levels (Pregnancy rate < 50%) showed a higher percentage of sperm with fragmented DNA compared to samples obtaining higher fertility levels. In conclusion, seasonal variations were found during the breeding season, obtaining lower sperm DNA fragmentation and higher pregnancy rates in spring. Additionally, samples with the highest proportion of sperm with fragmented DNA showed the lowest fertility levels throughout the breeding season.

中文翻译：

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在整个繁殖季节（春季和夏季）使用冷藏储存的种马精子进行人工授精后获得的精子 DNA 断裂和妊娠率的季节性变化

本研究的目的是评估繁殖季节（春季和夏季）不同时期的季节性变化，与冷藏保存的精液样本相关的种马精子 DNA 断裂和体内生育力。从 11 匹种马收集精液并评估精子活力（通过计算机辅助精子分析评估）和质膜完整性（在荧光显微镜下评估）。精子 DNA 片段化（通过精子染色质分散测试评估）在 5°C 下冷却储存的精液中进行了长达 24 小时的评估。在整个繁殖季节进行人工授精。母马每隔一天用冷却储存的精液（最多 24 小时）进行授精，直到排卵。每个周期的妊娠率是通过在排卵后 15 天通过超声检查检测胚胎囊泡来确定的。与夏季 (41.37 ± 10.81%) 相比，春季 (53.57 ± 9.97%) 的渐进式精子活力值 (平均值 ± SD) 显着更高 (P < 0.05)。不同季节间质膜完整性无​​显着差异（P > 0.05）。与夏季相比，春季精子 DNA 碎片化程度在 0 小时（4.81 ± 1.87% 对 8.77 ± 5.78%）、6 小时（9.00 ± 3.19% 对 18.73 ± 8.22%）和 24 小时（14.6）后显着降低（P < 0.01） 4.13% vs. 30.14 ± 9.85%) 的冷却存储。与夏季 (37%) 相比，春季 (50%) 每个周期的妊娠率也显着更高 (P < 0.01)。阳性妊娠与 DNA 片段化精子之间存在中度负相关（r = - 0.619；P < 0.001）。与中等生育水平相关的精液样本（妊娠率 < 50%) 显示与获得更高生育水平的样本相比，具有更高比例的 DNA 碎片化精子。总之，在繁殖季节发现了季节性变化，在春季获得较低的精子 DNA 碎片和较高的怀孕率。此外，在整个繁殖季节，DNA 片段精子比例最高的样本显示出最低的生育水平。