Modelagem da transferência de calor em galinhas poedeiras submetidas a diferentes desafios térmicos

Abstract

This study aimed at developing a heat balance model in laying hens and analyzing its performance besides simulating and verifying the influence of the thermal variables on sensitive and latent heat partitions. The data used in the development of the mathematical model was from an previously experiment carried out in climate-controlled wind tunnels in which ninety laying hens aged 28 weeks were submitted to the factorial combination of five dry-bulb temperatures (tair: 20, 24, 28, 32 and 36 ºC), two levels of relative humidity (RH: 40 and 60%), and three air velocities (Vair: 0.2, 0.7 and 1.4 m⋅s-1) totaling 30 thermal challenges with three replicates each. For the heat transfer model, the partitions of heat transferred to the bird’s body through conduction (Qbird), convection (QConv), radiation (QRad) and respiratory tract (QResp) were taken into account. Thus, data from thermal variables, cloacal and surface temperatures, respiratory rate (RR) and body weight of birds as well as the surrounding temperature (tunnel frame) were collected. Firstly, ANOVA and MANOVA were performed in order to adjust equations to the RR and the overall heat transfer coefficient by conduction in the bird's body (U), respectively. Twenty-four models using different input configurations for the convective heat transfer coefficient (hconv) and U were determined. The definition and validation of the best configuration were performed by comparing the predicted cloacal temperature values to those obtained experimentally. As a result, the model has proven its suitability for analyzing the interaction between the bird and the environment, and the complexity in determining U and hconv interferes with its performance. Based on Student's t-test (p<0.05) along with statistical indicators, constant values for such parameters are not recommended. U was affected by different levels of tar, RH and Var. For the conditions researched, the latent heat loss presented a larger contribution than the sensitive ways after 32.85 ºC temperature. The increase of Var raises Qbird and QConv rates but it does not change the QResp, however, further studies about its influence on QRad are needed. It is noteworthy that the model is accurate to predict the cloacal temperature, once it allows simulations of the birds' thermoregulation process and helps in the identification of possible strategies for mitigating thermal stress.