Abstract
Simple Summary The current study shows that using cold water under high ambient temperature (CW: 15 +/- 1 degrees C; HT: HT: 35 +/- 1 degrees C) in heat-exposed laying hens is capable of maintaining productive efficiency and immune-suppressing under heat stress. The feed intake and egg production were enhanced after using the cold water under heat stress. Moreover, the cold water restored the decline in the level of B-cell, helper T cells, and the ratio of helper/cytotoxic T cells in peripheral blood mononuclear cells, as well as the concentration of IL-2, IFN-gamma, and immunoglobulin G in plasma. Therefore, cold water is one of the mechanisms that can be considered under heat stress. This study aimed to investigate the effects of cold drinking water on cellular and humoral immunity in heat-exposed laying hens. One hundred and eight laying hens at 19 weeks old were placed into three treatments with six replicates of six hens in each group as follows: (1) hens were provided with normal drinking water (NW) under the control of thermoneutral temperature (CT: 25 +/- 1 degrees C; CT + NW), (2) hens were provided with NW under high ambient temperature (HT: 35 +/- 1 degrees C; HT + NW) for 8 h/d for a month, and (3) hens were treated under HT with cold drinking water (CW: 15 +/- 1 degrees C; HT + CW) for 8 h/d for a 4-weeks. Then, the feed consumption, egg production, egg weight, feed conversion ratio, and blood immune parameters were investigated. The results showed that cold drinking water (CW) caused a significant (p < 0.05) recovery in the reduction of food intake and egg production due to heat stress; however, there was no significant effect (p > 0.05) on egg weight and feed conversion ratio. Moreover, CW significantly (p < 0.05) restored the immune-suppressing effects of heat stress on the contents of peripheral blood mononuclear cells, including B-cell (BU-Ia), helper T cell (CD4), and the ratio of helper/cytotoxic T cell (CD4/CD8). In addition, CW significantly (p < 0.05) recovered the reduction on the level of mRNA expression of interleukin-2 (IL-2) and interferon-gamma (IFN-gamma), as well as significantly (p < 0.05) restored the reduction of plasma concentration of IL-2, IFN-gamma and immunoglobulin G in heat-stressed laying hens. These results prove that CW increased heat dissipation and enhanced feed intake, egg production, and cellular and humoral immunity in heat-exposed laying hens.