Heat transfer model for predicting hen’s core temperature

Abstract

The objective of this study was to develop a heat balance in laying hens and analyze their performance, besides simulating the partition between sensible and latent heats. The 28-d old Hy-line laying hens were subjected to a factorial combination of five levels of air temperature (20, 24, 28, 32, and 36 °C), two levels of air relative humidity (40 and 60%), and three levels of air velocity (0.2, 0.7 and 1.4 m∙s−1). The minimum and maximum exposure times for each bird to a given thermal challenge were 3 h and 6 h, respectively. Firstly, ANOVA and multiple regression were performed to fit equations of respiratory rate and the overall heat transfer coefficient by conduction in the bird's body (U), respectively. For the heat balance, the partitions of heat transferred to the bird’s body through conduction, convection, radiation and respiratory tract were taken into account. Different input settings were evaluated for convection heat transfer coefficient (hconv) and U. The validation of the proposed model was performed by comparing the predicted cloacal temperature values to those obtained experimentally. As a result, the model proved to be adequate for analyzing the interaction between hen and environment, and the complexity in determining U and hconv interferes in its performance. Statistical analysis reiterates that the use of constant values for these coefficients are not recommended. For the studied conditions, latent heat loss had a greater contribution than sensible forms from the temperature of 32.85 °C, not being influenced by air velocity. The model is accurate for the prediction of cloacal temperature, contributing to the identification of possible strategies for mitigating thermal stress, as it allows simulations of the thermoregulation mechanism of laying hens.