Oral Presentation The Annual Scientific Meeting of the Endocrine Society of Australia and the Society for Reproductive Biology 2014

Relationship between mitochondrial DNA haplotype and litter size in pigs (#147)

Tesha Tsai 1 , Sriram Rajasekar 1 , Justin St. John 1
  1. MIMR-PHI Institute of Medical Research, Clayton, VIC, Australia

Mitochondrial DNA (mtDNA) encodes proteins essential for oxidative phosphorylation, which generates the vast majority of cellular ATP. MtDNA also possesses the displacement (D) loop, which consists of two hypervariable regions that are used to determine maternal lineages. Variations in mtDNA can be advantageous for an animal to adapt to its specific environment. For example, certain mtDNA haplotypes are associated with improved milk quality and fertility traits in livestock. By sequencing the D loop region, we have identified five haplotypes from cohorts of commercial pigs in Australia. We compared litter size rates for each haplotype over multiple generations and determined that haplotypes C and D produced significantly more litters with ≥ 14 offspring per parity whilst sows from haplotype A produced significantly more litters with <10 offspring per parity. Using Brilliant Cresyl Blue (BCB) to select developmentally competent cumulus oocyte complexes (COCs) from each haplotype, we determined that the mean (± SEM) number of COCs staining positively for haplotype A, B, C, D and E were 12.5 ± 1.7, 13.3  ± 2.5, 21.0  ± 17, 12.6 ± 7.3, 11.6 ± 2.8, respectively. The mean (± SEM) number of COCs staining negatively for haplotype A, B, C, D and E were 22.7 ± 6.3, 20.7 ± 5.4, 10.5 ± 4.5, 28.4 ± 9.3, 24.7 ± 10.6, respectively. The total number of COCs obtained across all haplotypes was 42.2 ± 5. As mtDNA copy number is important to fertilization outcome, we quantified mtDNA copy number in BCB positive oocytes by real time PCR. We determined that oocytes from haplotypes C and D possessed significantly higher mtDNA copy number than for the other haplotypes. These outcomes demonstrate that mtDNA haplotypes influence oocyte developmental competence and litter size in commercial pigs.