Identification of Marbling Gene Loci in Commercial Pigs in Canadian Herds

A genome-wide association study (GWAS) was performed on the intramuscular fat percentage in pork chops in commercially available swine in Canada. The Duroc, Iberian, Lacombe, Berkshire, and Pietrain breeds were crossed with Large White sows, and their F1 offspring were ranked according to the intramuscular fat percentage (IMF %) obtained in their longissimus dorsi (LD) muscle loin chops. The ideal IMF % is considered to be >3%, whereas the average is ~1.5% in North American pork. The genetics of the top 10% and bottom 10% from our sample population were analysed by using 80,000 single nucleotide polymorphism (SNP) microarrays in the GWAS. Our sample population had an average IMF % of 2.5 ± 0.7%, but some pork achieved >7% IMF. GWAS analysis revealed SNP markers which were associated with the highest marbled pork chops on chromosomes 5, 7, and 16. Using the Sus scrofa/ susScr 11.1 map, we determined that the nearest genes were sarcospan ( SSPN ), Rh-associated glycoprotein ( RHAG ), and EGF-like fibronectin and laminin G ( EGFLAM ), which can be linked with muscular dystrophy disorders. We tested a subpopulation of Duroc-sired animals and found a different set of markers close to glycine receptor beta ( GRLB ) and potassium channel 3 ( KCNJ3 ) on chromosomes 8 and 15. Based on our results, we could achieve pork with a good IMF of >4% from animals commercially bred and raised to standard market weights of 110 kg. The choice of obtaining a good marbling line of pigs is not necessarily breed-specific, but it is line-specific.