Determination of mitochondrial function and site-specific defects in electron transport in duodenal mitochondria in broilers with low and high feed efficiency.

Duodenal mitochondria were isolated from broiler breeder males with high (0.79+/-0.01, n = 9) and low (0.63+/-0.02, n = 9) feed efficiency (FE) to assess relationships of FE with duodenal mitochondrial function and site-specific defects in electron transport. Sequential additions of adenosine diphosphate (ADP) resulted in 1) higher respiratory control ratio (RCR; an index of respiratory chain coupling) in high FE mitochondria provided succinate, and 2) higher ADP to oxygen ratio (ADP:O; an index of oxidative phosphorylation) in low FE mitochondria provided NADH-linked substrates (malate, pyruvate, or both). Basal electron leak, measured as H2O2 production, was greater in low FE mitochondria provided succinate (P = 0.08) or NADH-linked substrates. As H2O2 levels were elevated in low FE compared with high FE mitochondria by complex I (P+/-0.07) and complex II inhibition, the higher basal electron leak in low FE mitochondria was apparently due to site-specific defects in electron transport at complexes I and II. Elevations in H2O2 above basal levels indicated that high FE mitochondria may also exhibit electron transport defects at complexes I and III. Despite an ability to produce adenosine triphosphate (ATP) that was equal or superior to that demonstrated in high FE duodenal mitochondria, low FE mitochondria exhibited a greater inherent degree of electron leak. The results provide insight into the role that duodenal mitochondria play in the phenotypic expression of FE in broilers.