Abstract Heat stress (HS), whether constant or cyclic, poses a significant challenge to the poultry industry, leading to reduced performance, compromised animal welfare, and health issues. Despite its well-known effects, the specific impact of HS on muscle growth and development remains incompletely understood. This study investigated the effects of chronic cyclic mild HS on body weight (BW), breast muscle yield (BMY), meat quality, glycolytic metabolites and gene expression in breast muscles of finishing broilers. A total of 900 Ross 308 chicks (450 males and 450 females) were reared under thermoneutral (TN, n = 10 pens, 5 pens/sex, 45 birds/pen, 450 birds in total) or HS (n = 10 pens, 5 pens/sex, 45 birds/pen, 450 birds in total) conditions (30°C, 45% RH for 10 h/day from d 28 to d 34). On d 35, two birds per pen were sampled for meat quality and RNA-Seq analysis. HS reduced BW (P = 0.002) and Pectoralis major muscle yield (P = 0.02) and tended to decrease BMY (P = 0.06). Meat quality traits, glycolytic metabolites, and muscle protein functional properties were not affected (P 0.05), likely due to compensatory feed intake before and after HS exposure. Transcriptomic analysis revealed 301 differentially expressed genes (DEGs), including 138 downregulated and 163 upregulated genes under HS (|Log2FC| 1.0, P 0.05). Several downregulated DEGs showed significant positive correlations with BW and muscle mass. Functional enrichment indicated these genes were involved in structural pathways, including extracellular matrix-receptor interaction, cytoskeleton organization in muscle cells, and regulation of the actin cytoskeleton. These pathways are essential for muscle integrity, growth, and repair. Our findings suggest a previously underexplored mechanism by which HS impairs broiler performance through disruption of structural gene networks critical for muscle development.
Achour et al. (Fri,) studied this question.