Impact of exposure time to harsh environments on physiology, mortality, and thermal comfort of day-old chickens in a simulated condition of transport

Abstract

The aim of this study was to assess the variation of physiological responses and mortality of day-old chicks subjected to different thermal conditions and exposure times during simulated transport. For this purpose, day-old chicks (n\xa0=\u2009900) were used and subjected to simulated conditions of transport in a climate chamber. The experimental design was a completely randomized block design, with the structure of the treatments in a 3\u2009×\u20093 factorial scheme (thermal ranges and time intervals) and each level of containers considered a block. The physiological variables used in this trial were body weight, respiratory rate, cloacal temperature, average surface temperature, and gene expression of heat shock protein (HSP70). Regarding body weight, a small variation was observed between treatments (P\xa0>\u20090.05). The animals subjected to the heat treatment exhibited respiratory rates above 100 movements per minute (P\xa0<\u20090.05), average cloacal temperatures above 44.7\xa0°C, surface temperatures above the comfort zone (greater than 39.6\xa0°C; P\xa0<\u20090.05), and increased gene expression of HSP70 (P\xa0<\u20090.001), especially after 3 initial hours of exposure. In addition, the heat treatment lead to increased mortality of the animals (over 6%). Also in the cold treatment, despite the absence of mortality, the animals showed hypothermia from 3\xa0h of exposure, based on the results of the average surface (28\xa0°C) and cloacal temperatures (39.6\xa0°C; P\xa0<\u20090.05). In this way, the results imply that the effects of thermal stress caused by heat as well as by cold in a simulated transport condition are increased when traveling for more than 3\xa0h, indicating a trend of rising mortality after long-term transportation of day-old chickens.