Zhang F J, Weng X G, Wang J F, Zhou D, Zhang W, Zhai C C, Hou Y X, Zhu Y H
College of Veterinary Medicine, China Agricultural University, Beijing 100193, China Beijing Vocational College of Agriculture, Beijing 102442, China.
College of Veterinary Medicine, China Agricultural University, Beijing 100193, China.
J Anim Sci. 2014 Jul;92(7):3026-34. doi: 10.2527/jas.2013-6932. Epub 2014 May 30.
Heat stress adversely affects the productivity and immune status of dairy cows. The temperature-humidity index (THI) is commonly used to indicate the degree of heat stress on dairy cattle. We investigated the effects of different THI and Cr supplementation on the antioxidant capacity, the levels of heat shock protein 72 (Hsp72), and cytokine responses of lactating cows. The study used a total of 24 clinically healthy uniparous midlactation Holstein cows, which were randomly divided into 2 groups (n = 12 per group), and was conducted in 3 designated THI periods: low THI period (LTHI; THI = 56.4 ± 2.5), moderate THI period (MTHI; THI = 73.9 ± 1.7), and high THI period (HTHI; THI = 80.3 ± 1.0). The 2 groups of cows were fed corn and corn silage based basal diet supplemented chromium picolinate to provide 3.5 mg of Cr/cow daily (Cr+) or basal diet with no Cr (Cr-). The experiment was a 3 × 2 factorial design. The numbers of leukocytes (P < 0.05) and serum levels of glucose (P < 0.001) were lower; however, the serum levels of blood urea nitrogen (BUN; P < 0.001) and creatinine (P < 0.001) were greater in the MTHI and HTHI than in LTHI. The total antioxidant capacity in the serum was unaltered; an increase in superoxide dismutase activity (P < 0.001) and in serum malondialdehyde concentration (P < 0.001) was observed in the MTHI and HTHI compared with the LTHI. The high THI led to increases in serum concentrations of tumor necrosis factor-α (TNF-α; P < 0.001) and IL-10 (P < 0.05). Cows supplemented with Cr had lower (P = 0.009) serum concentrations of cholesterol but greater (P < 0.001, respectively) serum levels of Hsp72 and IL-10 compared with those without Cr supplementation in the HTHI. Western blot analysis revealed that cows supplemented with Cr had greater (P = 0.038) expression of the inhibitor of nuclear factor kappa B α (IκBα) in peripheral blood mononuclear cells (PBMC) compared with those without Cr supplementation in the HTHI, whereas the expression of Hsp72 in PBMC was unaltered. Data indicate that there is a decrease in glucose and increases in BUN and creatinine in the serum of midlactation cows under hot conditions during the summer and that these cows have a lowered oxidative capacity but an elevated antioxidant capacity. In addition, Cr may play an anti-inflammatory role in lactating cows by promoting the release of Hsp72, increasing the production of IL-10, and inhibiting the degradation of IκBα under hot conditions during the summer.
热应激对奶牛的生产性能和免疫状态产生不利影响。温度湿度指数（THI）通常用于指示奶牛热应激的程度。我们研究了不同THI和铬补充剂对泌乳奶牛抗氧化能力、热休克蛋白72（Hsp72）水平和细胞因子反应的影响。该研究共使用了24头临床健康的初产中期泌乳荷斯坦奶牛，随机分为2组（每组n = 12头），并在3个指定的THI时期进行：低THI时期（LTHI；THI = 56.4 ± 2.5）、中度THI时期（MTHI；THI = 73.9 ± 1.7）和高THI时期（HTHI；THI = 80.3 ± 1.0）。两组奶牛分别饲喂以玉米和玉米青贮为基础的日粮，其中一组补充吡啶甲酸铬，使每头奶牛每天摄入3.5 mg铬（Cr+），另一组不补充铬（Cr-）。该实验采用3×2析因设计。与LTHI相比，MTHI和HTHI时期白细胞数量（P < 0.05）和血清葡萄糖水平（P < 0.001）较低；然而，血清血尿素氮（BUN；P < 0.001）和肌酐水平（P < 0.001）较高。血清总抗氧化能力未改变；与LTHI相比，MTHI和HTHI时期超氧化物歧化酶活性增加（P < 0.001），血清丙二醛浓度增加（P < 0.001）。高THI导致血清肿瘤坏死因子-α（TNF-α；P < 0.001）和IL-10浓度升高（P < 0.05）。在HTHI时期，与未补充铬的奶牛相比，补充铬的奶牛血清胆固醇浓度较低（P =
0.009），但血清Hsp72和IL-10水平较高（分别为P < 0.001）。蛋白质免疫印迹分析显示，在HTHI时期，与未补充铬的奶牛相比，补充铬的奶牛外周血单核细胞（PBMC）中核因子κBα抑制剂（IκBα）的表达较高（P = 0.038），而PBMC中Hsp72的表达未改变。数据表明，夏季炎热条件下，中期泌乳奶牛血清中葡萄糖含量降低，BUN和肌酐含量升高，这些奶牛的氧化能力降低，但抗氧化能力升高。此外，铬可能通过在夏季炎热条件下促进Hsp72释放、增加IL-10产生和抑制IκBα降解，在泌乳奶牛中发挥抗炎作用。
