Broiler behavior: Influence of thermal stress, age, and period of the day

ABSTRACT This study evaluated the behavior of broiler chickens subjected to thermal stress during different periods of the day and age of birds. A total of 180 one-day-old male broiler chicks were allocated to three chambers. Each chamber contained five boxes, with 12 chicks/box. Birds were assigned to a completely randomized design. The birds were filmed, and the images recorded every minute during the two periods: morning (from 08:00 to 09:00 h) and afternoon (from 17:00 to 18:00 h), at 7, 14, and 35 d of age. The frequency of the behavioral category (water intake, feed intake, resting, exploration, and comfort) was determined. Data were subjected to variance analysis for mixed models with rearing temperatures (cold, usual, and hot) and age of birds (7, 14, and 35 d) as subdivided plot, and periods of the day (morning and afternoon) as sub-subdivided plot. Birds at cold and usual temperatures showed higher feed intake than those at hot temperature in the morning. Birds exposed to cold and usual temperatures explored the environment less frequently at 35 d when compared with 14 d. However, chickens at hot temperature showed decreased exploration according to the increase of age. Birds spent more time feeding during the morning, regardless of age and rearing temperature. Also, during this period of the day, chickens spent most of the time exploring the environment. The frequency of feed intake and exploration decreases with the increase of age. The similarity of behavior between chickens reared at cold and usual temperatures may be due to a change in the thermal comfort zone of the birds. It suggests that the real thermal comfort temperature is between the two temperature ranges studied (cold and usual).

摘要 本研究评估了肉鸡在一日中不同时段及不同日龄时遭受热应激的行为表现。试验共选用180只1日龄雄性肉鸡雏鸡，将其分配至三个环境舱内。每个环境舱设有5个饲养箱，每箱饲养12只雏鸡，试验采用完全随机设计方案。分别在肉鸡7、14和35日龄时，于两个观测时段（上午08:00至09:00、下午17:00至18:00）内每分钟拍摄并记录影像。随后统计各类行为（饮水、采食、静息、探索及舒适行为）的发生频率。数据采用混合模型进行方差分析，其中饲养温度（低温、常规温度、高温）与肉鸡日龄（7、14、35日龄）作为裂区因子，一日中的观测时段作为亚裂区因子。结果显示：上午时段内，低温与常规温度环境下的肉鸡采食频率显著高于高温环境组；与14日龄相比，35日龄时处于低温及常规温度环境的肉鸡探索环境的频率更低，而高温环境下的肉鸡探索行为频率随日龄增加呈下降趋势。无论日龄与饲养温度如何，肉鸡在上午时段的采食时长均更长，且该时段内肉鸡多数时间用于探索环境。采食与探索行为的发生频率随日龄增加而降低。低温与常规温度环境饲养的肉鸡行为模式相似，这可能与肉鸡自身热舒适区的改变有关。研究表明，肉鸡真实的热舒适温度处于本次试验所涵盖的两个温度区间（低温与常规温度）之间。