Drinking water temperature effects on laying hens subjected to warm cyclic environments

Two experiments were conducted to evaluate the effects of drinking water temperature (T_w) on laying hens subjected to warm cyclic air temperature (T_a) conditions. Each experiment consisted of a 1-wk acclimation under thermoneutrality (TN) (T_a = T_w = 21 C), a 4-wk heat exposure or treatment period, and a 2-wk recovery under TN. Each experiment involved 24 individually caged hens at the initial age of 29 wk (Experiment 1) or 30 wk (Experiment 2). In Experiment 1, T_w of 18 or 27 C was provided to 12 birds per T_w regimen under a diurnal T _a of 27 to 35 C (daily mean of 31 C). In Experiment 2, T_w of 15, 19, 23, or 27 C was provided to six birds per T_w regimen under a diurnal T_a of 27 to 38 C (daily mean of 32.5 C). Experiment 1 showed that T_w of 18 C enhanced hourly and daily feed and water intake during the first 2 wk of heat exposure, as compared with T_w of 27 C. Experiment 2 showed that daily feed and water intake were greatest for hens in the 23 C T_w regimen and least for hens in the coolest or warmest T_w regimens. Reduction in daily feed intake with increase in daily mean T_a ranged from 2.0-3.2 g/C-day (first week of heat exposure) to 1.1-1.9 g/C-day (fourth week of heat exposure). Water to feed intake ratio was 1.8-2.0 during acclimation and recovery, but increased to 3.0-3.4 during heat exposure. Internal egg quality parameters were in general unaffected by T_w. The two warmer T_w regimens in Experiment 2 had less reduction in egg size than did the two cooler T_w. In both experiments, hens displayed anticipatory increase in feed and water intake 2 to 3 h prior to lights-off. However, the stimulus of lights-on did not elicit a strong return to feed and water consumption as typically seen in broilers. The results revealed the potential existence of an optimal T_w range (near 23 C) for heat-challenged laying hens. Larger-scale tests are warranted to further verify the findings.