Global RNA expression in breast muscle obtained from a male broiler line phenotyped for high or low feed efficiency (FE) was investigated. Pooled RNA samples (n = 6/phenotype) labeled with cyanine 3 or cyanine 5 fluorescent dyes to generate cRNA probes were hybridized on a 4 × 44K chicken oligo microarray. Local polynomial regression normalization was applied to background-corrected red and green intensities with a moderated t-statistic. Corresponding P-values were computed and adjusted for multiple testing by false discovery rate to identify differentially expressed genes. Microarray validation was carried out by comparing findings with quantitative reverse-transcription PCR. A 1.3-fold difference in gene expression was set as a cutoff value, which encompassed 20% (782 of 4,011) of the total number of genes that were differentially expressed between FE phenotypes. Using an online software program (Ingenuity Pathway Analysis), the top 10 upregulated genes identified by Ingenuity Pathway Analysis in the high-FE group were generally associated with anabolic processes. In contrast, 7 of the top 10 downregulated genes in the high-FE phenotype (upregulated in the low-FE phenotype) were associated with muscle fiber development, muscle function, and cytoskeletal organization, with the remaining 3 genes associated with self-recognition or stress-responding genes. The results from this study focusing on only the top differentially expressed genes suggest that the high-FE broiler phenotype is derived from the upregulation of genes associated with anabolic processes as well as a downregulation of genes associated with muscle fiber development, muscle function, cytoskeletal organization, and stress response.

Global RNA expression in breast muscle obtained from a male broiler line phenotyped for high or low feed efficiency (FE) was investigated using microarray analysis. Microarray procedures and validation were reported previously. By using an overlay function of a software program (Ingenuity Pathway Analysis, IPA) in which canonical pathways are projected onto a set of genes, a subset of 27 differentially expressed focus genes were identified. Focus genes that were upregulated in the high FE phenotype were associated with important signal transduction pathways (Jnk, G-coupled, and retinoic acid) or in sensing cell energy status and stimulating energy production that would likely enhance growth and development of muscle tissue. In contrast, focus genes that were upregulated in the low FE muscle phenotype were associated with cytoskeletal architecture (e.g., actin-myosin filaments), fatty acid oxidation, growth factors, or ones that would likely be induced in response to oxidative stress. The results of this study provide additional information on gene expression and the cellular basis of feed efficiency in broilers.