KEGG pathway enrichment analysis of up-regulated DEGs (Figure 4B) showed that in the cardiac muscles of the lowland chickens the most enriched pathways (FDR <0.05) were “Jak-STAT signaling pathway,” “PPAR signaling pathway,” “purine metabolism,” “neuroactive ligand–receptor interaction,” and “p53 signaling,” while in the skeletal muscle tissue “cell cycle,” “MAPK signaling pathway,” “pathways in cancer,” “antigen processing and presentation,” and “p53 signaling pathway” were enriched. This evidence concerns the gene TP53 and cancer.