Transcriptomic analysis of hypothalamic responses to heat stress in modern and legacy chicken lines
Date
2015
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Publisher
University of Delaware
Abstract
Modern commercial broilers have been intensively selected for high growth rate, feed efficiency and meat yield. This enhanced genetic selection, at the expense of the functional efficiency of other physiological systems, has reduced their ability to withstand high temperatures compared with the legacy lines. Broilers reared under high temperatures have lower growth rates and feed efficiency compared to those raised at optimal temperatures. Maintenance of thermoregulation, feeding behavior and energy homeostasis is mainly controlled by the hypothalamus. Based on these factors, we hypothesize that heat stress may differentially impact the hypothalamic gene expression patterns in modern and legacy broiler lines. To explore this hypothesis, RNA-seq was used to study the hypothalamic transcriptomic responses to heat stress in modern and legacy broiler lines and identify the differentially expressed genes at day 28 and 42 post hatch. Chickens in the heat stress group were subjected to a temperature of 41°C for 10hrs daily, from day 21 post hatch, while the controls were maintained at 25°C. The body weights of the heat stress chickens were lower compared to the controls in both the lines, however the difference is only statistically significant in Ross 708 line, at both the time points. Among the 13,642 genes analyzed, 187 and 182 genes were differentially expressed in response to heat stress in Ross 708 and Illinois line, respectively, at day 28 post hatch. These included, genes encoding rate-limiting enzymes that are primarily involved in regulating feed intake. The transcriptional profiles, at day 42-post hatch, identified 91 genes in Ross 708 and 393 genes in Illinois lines that are differentially expressed. These genes were predominantly involved in immune regulation. However, genes associated with feed intake regulation were also differentially expressed in Illinois line. This study suggests that hypothalamic regulation of feed intake during heat stress may have affected the body weights in Ross and Illinois lines. This study provides a broader understanding of the mechanisms underlying heat stress response in the hypothalamus of modern and legacy chicken lines.