The Effect of Cooled Perches on Immunological Parameters of Caged White Leghorn Hens during the Hot Summer Months

The objective of this study was to determine if thermally cooled perches improve hen immunity during hot summer. White Leghorn pullets at 16 week of age were randomly assigned to 18 cages of 3 banks at 9 hens per cage. Each bank was assigned to 1 of the 3 treatments up to 32 week of age: 1) thermally cooled perches, 2) perches with ambient air, and 3) cages without perches. Hens were exposed to natural ambient temperatures from June through September 2013 in Indiana with a 4 h acute heat episode at 27.6 week of age. The packed cell volume, heterophil to lymphocyte (H/L) ratio, plasma concentrations of total IgG, and cytokines of interleukin-1β and interleukin-6, plus lipopolysaccharide-induced tumor necrosis factor-α factor were measured at both 27.6 and 32 week of age. The mRNA expressions of these cytokines, toll-like receptor-4, and inducible nitric oxide synthase were also examined in the spleen of 32 week-old hens. Except for H/L ratio, thermally cooled perches did not significantly improve currently measured immunological indicators. These results indicated that the ambient temperature of 2013 summer in Indiana (24°C, 17.1 to 33.1°C) was not high enough and the 4 h heat episode at 33.3°C (32 to 34.6°C) was insufficient in length to evoke severe heat stress in hens. However, cooled perch hens had a lower H/L ratio than both air perch hens and control hens at 27.6 week of age and it was still lower compared to control hens (P本研究旨在探究热冷却栖架（thermally cooled perches）是否可在炎热夏季提升蛋鸡的免疫机能。试验选取16周龄的白来航青年蛋鸡（White Leghorn pullets），将其随机分配至18个笼位，分为3排，每笼饲养9只蛋鸡。3排笼位分别接受3种处理直至32周龄：1）热冷却栖架组；2）常温空气栖架组；3）无栖架笼养对照组。试验于2013年6月至9月在印第安纳州开展，蛋鸡全程暴露于自然环境温度，且于27.6周龄时经历4小时急性热应激事件。 分别在27.6周龄与32周龄时，测定红细胞压积、异嗜性粒细胞与淋巴细胞比值（heterophil to lymphocyte, H/L）、血浆总IgG浓度、白细胞介素-1β（interleukin-1β）、白细胞介素-6（interleukin-6）以及脂多糖诱导的肿瘤坏死因子-α的含量；同时于32周龄时，检测32周龄蛋鸡的脾脏中上述细胞因子、toll样受体-4（toll-like receptor-4）以及诱导型一氧化氮合酶（inducible nitric oxide synthase）的mRNA表达水平。 除H/L比值外，热冷却栖架组并未显著提升本试验测定的各项免疫指标。上述结果表明，2013年印第安纳州夏季的环境温度（平均24℃，波动范围17.1~33.1℃）未达到足以诱发蛋鸡严重热应激的阈值，且33.3℃（波动范围32~34.6℃）的4小时急性热应激事件时长也不足以引发严重热应激。不过，在27.6周龄时，热冷却栖架组蛋鸡的H/L比值显著低于常温空气栖架组与对照组，且至32周龄时仍显著低于对照组（P