Thermal rearing environment effect on behavior and metabolic profile of laying hens

Abstract

For the trial, 54 Bovans White laying hens were used at 95 weeks of age and were housed in groups of three birds per cage. A completely randomized design was used with a factorial scheme of treatments 2 × 3 (rations with two energy densities × three thermal environments). Corn-soybean meal based diets with similar composition, differing only in energy levels, were obtained with soybean oil inclusion (2750 kcal and 3250 kcal metabolizable energy (ME)). Climate-controlled rooms were used to mimic a thermoneutral environment (TE) (average temperature of 24.3 °C and relative humidity of 62.3%), a hot environment (HE) (average temperature of 30.2 °C and relative air humidity of 58.8%), and a cool environment (CE) (average temperature of 17.7 °C and relative humidity of 98.5%). The behavior (ethology and vocalization), physiological parameters (cloacal temperature and heat emission), and metabolic profile (serum biochemistry) of laying hens were analyzed. Laying hens’ behavior was affected by levels of ME. With higher levels of ME, hens sat more frequently and spent more time eating when they received lower levels of ME in their diets. Laying hens under heat stress, ate, stopped, and walked more frequently than the group housed in a CE. The noise ratio (dB (A)) emitted by laying hens differed according to the thermal environment. Chickens reared in hot environments vocalized more than those raised in cool environments. Diets and thermal environments influence laying hen behaviors, with thermoneutral environments presenting greater comfort as evidenced by lower vocalization. Diets with 3250 kcal of ME present greater control of body heat reflected in lower production of adrenalin and lactate serum levels (g/L). A thermal environment above a TE is more stressful to laying hens than the CE; thus, a TE is recommended to improve laying hens’ welfare.