BACKGROUND In dairy herds, mastitis causes detrimental economic losses. Genetic selection offers a sustainable tool to select animals with reduced susceptibility towards postpartum diseases. Studying underlying mechanisms is important to assess the physiological processes that cause differences between selected haplotypes. Therefore, the objective of this study was to establish an in vivo infection model to study the impact of selecting for alternative paternal haplotypes in a particular genomic region on cattle chromosome 18 for mastitis susceptibility under defined conditions in uniparous dairy cows. RESULTS At the start of pathogen challenge, no significant differences between the favorable (Q) and unfavorable (q) haplotypes were detected. Intramammary infection (IMI) with Staphylococcus aureus 1027 (S. aureus, n = 24, 96 h) or Escherichia coli 1303 (E. coli, n = 12, 24 h) was successfully induced in all uniparous cows. This finding was confirmed by clinical signs of mastitis and repeated recovery of the respective pathogen from milk samples of challenged quarters in each animal. After S. aureus challenge, Q-uniparous cows showed lower somatic cell counts 24 h and 36 h after challenge (P < 0.05), lower bacterial shedding in milk 12 h after challenge (P < 0.01) and a minor decrease in total milk yield 12 h and 24 h after challenge (P < 0.01) compared to q-uniparous cows. CONCLUSION An in vivo infection model to study the impact of genetic selection for mastitis susceptibility under defined conditions in uniparous dairy cows was successfully established and revealed significant differences between the two genetically selected haplotype groups. This result might explain their differences in susceptibility towards IMI. These clinical findings form the basis for further in-depth molecular analysis to clarify the underlying genetic mechanisms for mastitis resistance.

中文翻译：

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用于研究遗传变异对单头奶牛乳腺炎临床结局影响的体内模型。

背景技术在奶牛群中，乳腺炎造成有害的经济损失。遗传选择为选择对产后疾病易感性低的动物提供了一种可持续的工具。研究潜在的机制对于评估导致所选单倍型之间差异的生理过程很重要。因此，本研究的目的是建立体内感染模型，以研究在特定条件下选择特定基因组区域的替代父本单倍型对牛染色体18的乳腺炎易感性的影响。结果在病原体攻击开始时，未检测到有利（Q）和不利（q）单倍型之间的显着差异。金黄色葡萄球菌1027（金黄色葡萄球菌，n = 24，96 h）或大肠埃希氏菌1303（大肠杆菌，n = 12、24 h）在所有单头牛中均成功诱导。乳腺炎的临床体征以及从每只动物的受攻击处所的牛奶样品中反复回收相应病原体证实了这一发现。在金黄色葡萄球菌攻击后，Q-单头母牛在攻击后24 h和36 h的体细胞计数较低（P <0.05），在攻击后12 h牛奶中的细菌脱落较低（P <0.01），总产奶量略有下降攻击后12小时和24小时（P <0.01）与单胎牛相比。结论成功建立了体内感染模型，以研究遗传选择对特定条件下单头奶牛乳腺炎易感性的影响，并揭示了两个遗传选择的单倍型组之间的显着差异。该结果可能解释了他们对IMI敏感性的差异。这些临床发现为进一步深入的分子分析奠定基础，以阐明乳腺炎抵抗力的潜在遗传机制。