Modeling the performance of broilers under heat stress

Abstract

A meta-analysis was developed to model performance depression in heat stress (HS), to analyze the influence of HS type (cyclic or constant), and to assess the correlation between dietary electrolyte bal- ance (DEB) and HS in broilers. Two databases (Dat) with performance and temperature were constructed (initial phase − up to 21 d of age − 14 articles, 7,667 ani- mals, average replicate number treatment-ARN/T, 5 and growing phase − over 21 d of age − 74 articles and 25,145 broilers, ARN/T, 7). The criteria for article selec- tion were (1) experiments using at least 2 temperatures (thermoneutral and high temperature); (2) results of ADFI and ADG; (3) feed and water ad libitum during the experiment. Each treatment was classified as cyclic or constant HS and the HS group response was calcu- lated relative to the thermoneutral group. Performance was evaluated as raw data or as relativized information (indicated as “HS effect or 61⁄4”), expressed as a percentage of the difference between results. The models to predict “HS effect” showed that for the initial phase, only ADG was influenced by HS, while for the grower phase, pre- diction equations were created for ADFI and ADG. Con- sidering the simplest models, there was a reduction of 1.4% in ADFI and 2.1% in ADG for each unit (°C) above the upper critical temperature for broilers older than 21 d. Feed conversion (FC) was not affected by HS in any of the studied phases. Constant HS proved to be more negative than cyclic HS to broiler performance after 21 d of age. The relation between DEB and performance of broilers under HS was analyzed considering broilers over 21 d of age, and very weak correlations were observed. It was concluded that HS affects broilers over 21 d more, although FC is not affected. ADFI is the most important variable affected by HS and the relation between the DEB of the diet and HS is very weak. The empirical models generated in this study accurately predicted ADG and ADFI of broilers exposed to HS and can be used to minimize those effects on poultry production.