Overconditioned dairy cows are prone to greater insulin resistance in transition to successfully adapt to negative energy balance. The associations among body condition score (BCS), insulin resistance, lipid metabolism and oxidative stress in cows during late lactation with positive energy balance remain to be elucidated. The objectives of this study were to investigate insulin sensitivity and oxidative status in late lactating dairy cows with different BCS but similar milk production, parity and days in milk. Forty-two multiparous Holstein cows were fed the same diet under the same management and divided into three groups based on BCS: low BCS (LBCS; BCS ≤ 2.75; n = 12), medium BCS (MBCS; 3.0 ≤ BCS ≤ 3.5; n = 15) or high BCS (HBCS; BCS ≥ 3.75; n = 15). Blood samples used for analysis of biochemical and hematological parameters were collected from the coccygeal vein at the end of experiment. The concentrations of insulin and nonesterified fatty acid were higher and the revised quantitative insulin sensitivity check index (RQUICKI) was lower in HBCS cows than in LBCS and MBCS cows. These results suggest that insulin resistance exacerbates lipolysis in HBCS cows. Serum concentrations of very low-density lipoprotein, apolipoprotein A-I, and apolipoprotein B were lower in HBCS cows than in LBCS or MBCS cows. Although LBCS and MBCS cows had higher reactive oxygen species levels than did HBCS cows, the malondialdehyde concentration was not different among cows with different BCS. Ceruloplasmin activity was higher in MBCS and HBCS cows than in LBCS cows, but superoxide dismutase, glutathione peroxidase, and paraoxonase activities were not different among cows with different BCS. Despite the higher percentage of granulocytes in MBCS cows than in HBCS cows, no differences were found in leukocyte counts, red blood cell profiles and platelet profiles among the cows in the three groups. Results of this study showed that compared with MBCS and LBCS cows, HBCS cows at late lactation stage may have accumulated more hepatic triacylglycerol and lower antioxidant potential due to greater insulin resistance.

中文翻译：

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身体状况对泌乳奶牛胰岛素抵抗，脂质代谢和氧化应激的影响

过度适应的奶牛在过渡过程中容易产生更大的胰岛素抵抗，从而成功适应负能量平衡。泌乳晚期，能量平衡为正的母牛的身体状况评分（BCS），胰岛素抵抗，脂质代谢和氧化应激之间的关系仍有待阐明。这项研究的目的是调查具有不同BCS但奶产量，胎次和产奶天数相似的泌乳晚期奶牛的胰岛素敏感性和氧化状态。42只多头荷斯坦奶牛在相同管理下饲喂相同的日粮，并根据BCS分为三组：低BCS（LBCS; BCS≤2.75; n = 12），中BCS（MBCS; 3.0≤BCS≤3.5; n = 15）或高BCS（HBCS; BCS≥3.75; n = 15）。在实验结束时从尾静脉收集用于生化和血液学参数分析的血样。与LBCS和MBCS奶牛相比，HBCS奶牛的胰岛素和非酯化脂肪酸浓度更高，修订的定量胰岛素敏感性检查指数（RQUICKI）更低。这些结果表明，胰岛素抵抗加剧了HBCS奶牛的脂解作用。HBCS奶牛的极低密度脂蛋白，载脂蛋白AI和载脂蛋白B的血清浓度低于LBCS或MBCS奶牛。尽管LBCS和MBCS奶牛的活性氧水平高于HBCS奶牛，但不同BCS奶牛的丙二醛浓度没有差异。MBCS和HBCS奶牛的铜蓝蛋白活性高于LBCS奶牛，但是超氧化物歧化酶，谷胱甘肽过氧化物酶，BCS不同的奶牛对氧磷酶的活性无差异。尽管MBCS奶牛的粒细胞百分比高于HBCS奶牛，但三组奶牛的白细胞计数，红血球分布和血小板分布没有差异。这项研究的结果表明，与MBCS和LBCS奶牛相比，处于泌乳后期的HBCS奶牛可能会积累更多的肝三酰甘油，并且由于更高的胰岛素抵抗而降低了其抗氧化能力。