Department of Animal Sciences, University of Florida, Gainesville 32611.
Department of Ruminant Sciences, Institute of Animal Science, ARO Volcani Center, Rishon Lezion, Israel, 7505101.
J Dairy Sci. 2018 Jan;101(1):705-716. doi: 10.3168/jds.2017-13258. Epub 2017 Nov 8.
Heat stress negatively affects cow performance, compromises immune function, and increases susceptibility to metabolic disorders, particularly during the dry period and as cows transition from gestation to lactation. Metabolic adaptations of the liver are critical for successful transition, yet it is unclear how heat stress affects metabolic pathways within the liver at the proteomic level. The objective of this study was to investigate the liver proteome of postpartum cows that were cooled or heat stressed during the dry period to gain insight into how protein expression is altered by prior heat stress and may contribute to performance and disease outcomes. During the dry period, cows were either housed in shaded barns with fans and water soakers [cooled group (CL); n = 5] or in shaded barns lacking these cooling devices [heat-stressed group (HT); n = 5]. Liver biopsies were collected at 2 d postpartum, and protein content was analyzed by label-free quantitative shotgun proteomics (nanoscale liquid chromatography coupled to tandem mass spectrometry). In the most comprehensive bovine liver proteomics analysis completed to date, we identified 3,270 proteins, 75 of which were differentially expressed between HT and CL cows (fold change ±1.2). The top pathways differing between HT and CL cows were oxidative phosphorylation, mitochondrial dysfunction, farnesoid X receptor/retinoid X receptor (FXR/RXR) activation, and the methylmalonyl pathway. Cooling cows during the dry period likely improves ATP production, reduces oxidative stress, and prevents excessive accumulation of hepatic triglycerides and cholesterol, which may contribute to greater milk yield and lower susceptibility to transition-related diseases.
热应激会对奶牛的生产性能产生负面影响，降低其免疫功能，增加其患代谢紊乱疾病的易感性，特别是在干奶期和奶牛从妊娠过渡到泌乳期期间。肝脏的代谢适应对于成功过渡至关重要，但目前尚不清楚热应激如何在蛋白质组学水平上影响肝脏内的代谢途径。本研究的目的是研究产后奶牛的肝脏蛋白质组，这些奶牛在干奶期受到冷却或热应激，以深入了解先前的热应激如何改变蛋白质表达，并可能影响生产性能和疾病结果。在干奶期，奶牛要么被安置在带有风扇和水喷淋器的遮阳棚中（冷却组，CL；n = 5），要么被安置在缺乏这些冷却设备的遮阳棚中（热应激组，HT；n = 5）。在产后 2 天采集肝脏活检，并通过无标记定量 shotgun 蛋白质组学（纳米级液相色谱与串联质谱联用）分析蛋白质含量。在迄今为止完成的最全面的牛肝脏蛋白质组学分析中，我们鉴定了 3270 种蛋白质，其中 75 种在 HT 和 CL 奶牛之间存在差异表达（差异倍数 ±1.2）。HT 和 CL 奶牛之间差异最大的途径是氧化磷酸化、线粒体功能障碍、法尼醇 X 受体/视黄醇 X 受体（FXR/RXR）激活和甲基丙二酰途径。在干奶期给奶牛降温可能会提高 ATP 产量，减少氧化应激，并防止肝脏甘油三酯和胆固醇的过度积累，这可能有助于提高产奶量并降低对过渡相关疾病的易感性。
