Assessing and modeling responses of broiler chicks in the first three weeks of line subjected to thermal challenge of different intensities and durations

Abstract

Among the challenges involving the poultry industry, the thermal environment stands out, since unsuitable thermal environmental conditions decrease welfare of the birds and can negatively impact the productive performance. Thus, the aim of this research was to evaluate the productive (body mass, feed intake, water intake), physiological (cloacal temperature) and behavioral responses of Cobb broilers, 2-21 days old, to different temperatures (27, 30, 33 and 36°C) for different durations (from 1 to 4 days), starting on the second day of life. After the thermal stress challenge, birds were returned to the age-dependent thermoneutral temperature (32-35 °C). The experiment was conducted in four steps, using four environmentally-controlled wind tunnels. Two hundred and ten (210) male and female broilers at 1 to 22 days of age were used in the experiment, during which feed and water were provided ad libitum. Analysis of variance was used to assess the effect of thermal conditions and duration of thermal challenge on the response variables. Mathematical models based on artificial intelligence (Artificial Neural Network and Neuro-Fuzzy Networks) were developed and validated for predicting body mass of the broilers. Behavioral analysis of the birds subjected to the thermal challenges was performed using the hierarchy clustering method. Among the two tested modeling methods, Artificial Neural Network was more suitable for predicting body mass of chicks with an R² of 0.9993 and a standard error of 4.62 g. Four empirical models for the estimation of body mass, feed intake, water intake and cloacal temperature were developed, with coefficient of determination (R²) of 0.998, 0.980, 0.984 and 0.784, respectively, indicating good fit in the estimation. It is noteworthy that the factorial effects of air temperature, bird age and duration of thermal challenge was significant only for cloacal temperature. For body mass, feed intake and body intake, it was possible to verify only double interaction (air temperature and bird age). Furthermore, there is a residual effect, at six days of age, for duration of heat stress on the cloacal temperature. The behaviors of the birds were grouped utilizing dendograms in which the similarity of these data was qualified. Thus, the birds subjected to 27 and 30°C presented a similar, spending similar period of time huddling or spreading-apart. On the other hand, the birds at 30°C and 33°C spent a similar period of time at the drinkers and/or the feeders.