Thermoneutral zone for laying hens based on environmental conditions, enthalpy and thermal comfort indexes

Controlling environmental conditions inside laying hens facilities systems and their effects on physiology and performance is essential in defining management strategies to alleviate the adverse effects of thermal stress in laying hens. Thus, we estimated thermoneutral zones for laying hens exposed to different heat-challenging conditions based on environmental conditions, enthalpy, and thermal comfort indexes being evaluated out in four thermal environment-controlled wind tunnels equipped with heating and air moistening function, housed in an experimental room with an area of 31.92 m². Clustering analysis and empirical models were used to estimate thermoneutral zones for laying hens based on environmental conditions, enthalpy and thermal comfort indexes, and compare them with data available in the literature through graphics. The thermoneutral zones characterizing homeostasis for laying hens based on respiration rate (RR) are as follows: from 25.9 to 29.9 °C for air dry-bulb temperature (t_db), from 67 to 75 for temperature-humidity index (THI), from 68 to 73 for black globe-humidity index (BGHI), from 45 to 56 kJ kg dry air^-1 for enthalpy (H) and 441.7-465.6 W for radiant heat load (RHL). Comfort limits for physiological responses cloacal temperature (t_clo), surface temperature (t_sur) and RR found in this study are 39.4-39.9 °C, 26.5 to 29.9 °C and 30 to 67 mov. min^-1, respectively. The number of repetitions and the use of mathematical modeling to be worked on, may directly impact the amplitude of each limit to be established for each variable of interest.