Since behavioural adjustments are an important line of defence against thermal stress, either due to their energy efficiency or to efficiency at preventing overheating, we aimed to evaluate whether broilers fed different maize particle sizes adjusted their behaviour to deal with heat stress challenges. At several times a day, the behaviour of 220 naked neck broilers was evaluated. These broilers were fed with isonutritive diets containing maize with different geometric mean diameters (GMD): 605 and 2280 μm. The thermal environment was monitored during the experiment. Panting and open wings were the only behaviours that showed differences between the times of day (P < 0.05). However, GMD showed a significant effect on feed intake and panting (P < 0.05). The interaction between GMD and time of day was significant only on panting (P < 0.05). Although no daily variation was observed, the highest feed intake was observed in broilers fed the diet containing maize with a GMD of 2280 μm. Less than 5% of the broilers were observed drinking water during the day. Open wings was the behavioural adjustment most used by broilers from 10:00 h, and remained elevated until 14:00 h for both GMDs. The birds panted more when fed the diet containing maize with a GMD of 2280 μm. In conclusion, broilers adjust their behaviour to dissipate excess body heat from the environment and as a result of feed intake. Coarse particles of maize in the diet increase the thermal challenge of broilers since the environment also provides stressful thermal conditions.

中文翻译：

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肉鸡在承受自然热应激并在日粮中饲喂不同粒度的玉米时的行为调整

由于行为调整是抵御热应激的重要防线，无论是由于其能源效率还是防止过热的效率，我们旨在评估饲喂不同玉米粒度的肉鸡是否调整其行为以应对热应激挑战。每天多次评估 220 只裸颈肉鸡的行为。这些肉鸡饲喂含有不同几何平均直径 (GMD)：605 和 2280 μm 的玉米的等营养日粮。在实验过程中监测热环境。喘气和张开翅膀是唯一表现出一天中不同时间差异的行为（磷< 0.05)。然而，GMD 对采食量和喘气有显着影响（磷< 0.05)。GMD 和一天中的时间之间的交互作用仅在喘气时显着（磷< 0.05)。虽然没有观察到每日变化，但在饲喂 GMD 为 2280 μm 的玉米日粮的肉鸡中观察到最高的采食量。观察到不到 5% 的肉鸡在白天喝水。张开翅膀是肉鸡从 10:00 开始最常使用的行为调整，并且对于两种 GMD 都保持升高到 14:00。当喂食含有 GMD 为 2280 微米的玉米的饮食时，这些鸟儿喘气更多。总之，肉鸡通过调整它们的行为来消散来自环境和采食量的多余体热。日粮中的粗玉米颗粒增加了肉鸡的热挑战，因为环境也提供了应激性热条件。