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Potential Roles of mTOR and Protein Degradation Pathways in the Phenotypic Expression of Feed Efficiency in Broilers

Walter G. Bottje, Byung-Whi Kong, Jeong Yoon Lee, Tyrone Washington, Jami Baum, Sami Dridi, Terry Wing and John Hardiman

The cost of feed represents as much as 70% of the total cost of raising a meat producing animal to market weight. Thus, feed efficiency (FE; g gain: g feed) is a very important genetic trait in animal agriculture. We have observed that a hallmark of low feed efficiency in a highly selected male broiler (meat chicken) line was extensive protein oxidation that probably resulted from increased reactive oxygen species being produced by the mitochondria. Repair or resynthesis of damaged proteins would therefore represent a considerable energetic drain and contribute to the phenotypic expression of low feed efficiency. In the present study, a software program (Ingenuity Pathway Analysis, IPA) facilitated the analysis and interpretation of data from a 4 x 44k chicken oligo array on breast muscle along with data from previous studies obtained from broilers individually phenotyped for FE. The findings support a hypothesis that differential expression of genes associated with the Akt/mTOR, protein ubiquitination, and proteasome pathways through modulation of transcription and protein turnover could play an important role in the phenotypic expression of feed efficiency. Confirmation of this hypothesis will require a thorough assessment of protein expression as well as protein and enzyme activity measurements associated with these pathways in the low and high FE broiler phenotypes.