1 Department of Animal Science, Iowa State University, Ames, IA, 50011, USA.
2 Zinpro Corporation, Eden Prairie, MN, 55344, USA.
Animal. 2014 Jan;8(1):43-50. doi: 10.1017/S1751731113001961. Epub 2013 Nov 7.
Heat stress (HS) jeopardizes livestock health and productivity and both may in part be mediated by reduced intestinal integrity. Dietary zinc improves a variety of bowel diseases, which are characterized by increased intestinal permeability. Study objectives were to evaluate the effects of supplemental zinc amino acid complex (ZnAA) on intestinal integrity in heat-stressed growing pigs. Crossbred gilts (43±6 kg BW) were ad libitum fed one of three diets: (1) control (ZnC; 120 ppm Zn as ZnSO4; n=13), (2) control+100 ppm Zn as ZnAA (Zn220; containing a total of 220 ppm Zn; n=14), and (3) control+200 ppm Zn as ZnAA (Zn320; containing a total of 320 ppm Zn; n=16). After 25 days on their respective diets, all pigs were exposed to constant HS conditions (36°C, ∼50% humidity) for either 1 or 7 days. At the end of the environmental exposure, pigs were euthanized and blood and intestinal tissues were harvested immediately after sacrifice. As expected, HS increased rectal temperature (P⩽0.01; 40.23°C v. 38.93°C) and respiratory rate (P⩽0.01; 113 v. 36 bpm). Pigs receiving ZnAA tended to have increased rectal temperature (P=0.07; +0.27°C) compared with ZnC-fed pigs. HS markedly reduced feed intake (FI; P⩽0.01; 59%) and caused BW loss (2.10 kg), but neither variable was affected by dietary treatment. Fresh intestinal segments were assessed ex vivo for intestinal integrity. As HS progressed from days 1 to 7, both ileal and colonic transepithelial electrical resistance (TER) decreased (P⩽0.05; 34% and 22%, respectively). This was mirrored by an increase in ileal and colonic permeability to the macromolecule dextran (P⩽0.01; 13- and 56-fold, respectively), and increased colonic lipopolysaccharide permeability (P⩽0.05; threefold) with time. There was a quadratic response (P⩽0.05) to increasing ZnAA on ileal TER, as it was improved (P⩽0.05; 56%) in Zn220-fed pigs compared with ZnC. This study demonstrates that HS progressively compromises the intestinal barrier and supplementing ZnAA at the appropriate dose can improve aspects of small intestinal integrity during severe HS.
热应激（HS）危害家畜健康和生产力，这两者可能部分是通过降低肠道完整性介导的。膳食锌可改善多种肠道疾病，这些疾病的特征是肠道通透性增加。本研究的目的是评估补充锌氨基酸复合物（ZnAA）对热应激生长猪肠道完整性的影响。杂交母猪（43±6 kg BW）自由采食三种日粮中的一种：（1）对照（ZnC；120 ppm Zn 作为 ZnSO4；n=13），（2）对照+100 ppm Zn 作为 ZnAA（Zn220；总共含有 220 ppm Zn；n=14），和（3）对照+200 ppm Zn 作为 ZnAA（Zn320；总共含有 320 ppm Zn；n=16）。在各自的日粮上饲养 25 天后，所有猪都暴露于恒定的 HS 条件（36°C，约 50%湿度）下 1 或 7 天。在环境暴露结束时，猪被安乐死，在处死后立即采集血液和肠道组织。如预期的那样，HS 增加了直肠温度（P ⩽0.01；40.23°C v. 38.93°C）和呼吸频率（P ⩽0.01；113 v. 36 bpm）。与 ZnC 喂养的猪相比，接受 ZnAA 的猪直肠温度升高（P=0.07；+0.27°C）。HS 显著降低采食量（FI；P ⩽0.01；59%）并导致 BW 损失（2.10 kg），但这两个变量都不受日粮处理的影响。新鲜的肠道段在体外评估肠道完整性。随着 HS 从第 1 天进展到第 7 天，回肠和结肠的跨上皮电阻（TER）都降低（P ⩽0.05；分别降低 34%和 22%）。这与回肠和结肠对大分子葡聚糖的通透性增加（P ⩽0.01；分别增加 13-和 56 倍）以及结肠脂多糖通透性增加（P ⩽0.05；增加三倍）相对应。随着时间的推移，对 ZnAA 的反应呈二次（P ⩽0.05），回肠 TER 得到改善（P ⩽0.05；56%），Zn220 喂养的猪比 ZnC 喂养的猪有改善。本研究表明，HS 逐渐损害肠道屏障，在严重 HS 时适当补充 ZnAA 可以改善小肠完整性的某些方面。
