Association between mitochondrial DNA copy number and production traits in pigs

Mitochondria are essential organelles in the regulation of cellular energetic metabolism. Mitochondrial DNA copy number (mtDNA_CN) can be used as a proxy for mitochondria number, size, and activity. The aims of our study are to evaluate the effect of mtDNA_CN and mitochondrial haploblocks on production traits in pigs, and to identify the genetic background of this cellular phenotype. We collected performance data of 234 pigs and extracted DNA from skeletal muscle. Whole-genome sequencing data was used to determine mtDNA_CN. We detected positive correlations of muscle mtDNA_CN with backfat thickness at 207 d (+0.14; p-value = 0.07), and negative correlations with carcase loin thickness (-0.14; p-value = 0.03). Pigs with less mtDNA_CN had greater loin thickness (+4.1 mm; p-value = 0.01) and lower backfat thickness (-1.1 mm; p-value = 0.08), which resulted in greater carcase lean percentage (+2.4%; p-value = 0.04) than pigs with high mtDNA_CN. These results support the hypothesis that a reduction of mitochondrial activity is associated with greater feed efficiency. Pork from pigs with less mtDNA_CN may also tend to have lower ultimate pH (correlation: +0.19; p-value < 0.01). We found no association of the most frequent mitochondrial haploblocks with mtDNA_CN or the production traits, but several genomic regions that harbour potential candidate genes with functions related to mitochondrial biogenesis and homeostasis were associated to mtDNA_CN. These regions provide new insights into the genetic background of this cellular phenotype but it is still uncertain if such associations translate into noticeable effects on the production traits.