Thermal environment and physiological and productive parameters in laying hens: assessment and modeling

Abstract

This study aimed to evaluate and model mathematically the effect of the thermal environment on the physiological responses of laying hens. The study was conducted in four air-conditioned wind tunnels, where ninety laying hens in peak production phase, aged 28 weeks, were housed individually in a cage and subjected to different thermal challenges. The birds were subjected to the factorial combination of five dry air bulb temperatures (tbs: 20, 24, 28, 32 and 36ºC), two levels of relative humidity (RH: 40 and 60%) and three air velocities (V: 0.2, 0.7 and 1.4 m s-1), totaling 30 thermal challenges. The physiological responses surface temperature (tsurface), cloacal temperature (tcloacal) and respiratory rate (RR) were measured at 10 min intervals during each experimental test (thermal challenge), with a minimum duration of three hours and a maximum duration of six hours. Empirical models were adjusted and models based on artificial intelligence (Artificial Neural Network - ANNs and fuzzy systems) were developed to predict the physiological responses of laying hens as a function of the variables that characterize the different thermal challenges. In addition, thermal comfort ranges have been established for birds as a result of these variables. Through the analysis of clusters, empirical models and graphics with thermal comfort bands for Hy Line laying hens, it can be inferred that, in a controlled experimental environment, the comfort bands found are close to those specified by the literature. The development of models based on artificial intelligence (fuzzy and ANNs) mainly due to the climatic variables, tbs, RH, V, obtained adequate adjustments to predict the tcloacal, tsurface and RR physiological variables.