Mitochondrial genes and antioxidant mechanisms in the duodenum relate to feed efficiency in slow-growing chickens

The aim of this study was to investigate the expression of mitochondrial oxidative phosphorylation (OXPHOS) genes, oxidative stress, and antioxidant responses in the duodenum, involved in differential residual feed intake (RFI), an indicator of feed efficiency. The study was conducted on two groups of 15 male slow-growing Korat chickens (KRC), the low RFI (LRFI) group and the high RFI (HRFI) group, with mean values of -197.8 ± 12.1 g and 200.8 ± 15.1 g, respectively. The results indicated that differences in RFI did not negatively affect growth performance (P>0.05). The LRFI group had a significantly lower feed intake than the HRFI group (P<0.05). Expression profiles of mitochondrial OXPHOS genes showed that COX1, COX2, COX3, CYTB, ND2, ND5, ATP6, and ATP8 were upregulated in HRFI chickens (P<0.05), indicating a higher mitochondrial activity related to cellular respiration for energy production. This was consistent with the higher oxidative stress indicated by increased reactive oxygen species (ROS) production observed in HRFI chickens. Moreover, the antioxidant enzyme activities in HRFI were significantly higher than those in LRFI, suggesting that HRFI birds have the capacity to cope with elevated levels of ROS. Principal component analysis (PCA), which integrated phenotypic characterization, mitochondrial oxidative status, and gene expression levels, revealed a clear separation between LRFI and HRFI chickens, with PC-1 explaining 47% of the variance. Mitochondrial OXPHOS genes and oxidative stress-related traits clustered toward the HRFI group, indicating a positive correlation between reduced feed efficiency, oxidative metabolism to produce energy, and elevated oxidative stress. This study demonstrates that differences in feed efficiency in KRC were associated with differences in mitochondrial function related to cellular respiration and antioxidant enzyme mechanisms, which eliminate ROS produced during cellular respiration. The findings suggested that HRFI chickens had greater energy demands compared to LRFI chickens.