design: Sus scrofa ovarian mitochondrial fraction was enriched and total DNAs were extracted by QIAGEN DNeasy Blood & Tissue kit. Enriched mtDNAs, lambda DNA (dam-: dcm-) and pBR322 plasmid DNA were digested by EcoRV, purified and mixed together.  BS-seq library was constructed from EcoRV digested mtDNA mixture by using Zymo Pico Methyl-Seq Library Prep Kit, according to the manufacturers instructions.  Each NGS library was sequenced by Illumina NextSeq instrument using 150 bp paired-end sequencing v2.5 chemistry.