Identification of Single Nucleotide Polymorphisms in Porcine <i>MAOA</i> Gene Associated with Aggressive Behavior of Weaned Pigs after Group Mixing

Understanding the genetic background underlying the expression of behavioral traits has the potential to fasten the genetic progress for reduced aggressive behavior of pigs. The monoamine oxidase A (<i>MAOA</i>) gene is known as the &#8220;warrior&#8221; gene, as it has been previously linked to aggressive behavior in humans and livestock animals. To identify single nucleotide polymorphisms in porcine <i>MAOA</i> gene associated with aggressive behavior of pigs, a total of 500 weaned pigs were selected and mixed in 51 pens. In each pen, two aggressive and two docile pigs (a total of 204 pigs) were selected based on their composite aggressive score (CAS). Ear tissue was sampled to extract genomic DNA. Constructs containing variable lengths of truncated porcine <i>MAOA</i> promoter were used to determine the promoter activity by a dual luciferase reporter system. The core promoter region was located at &#8722;679 bp to &#8722;400 bp. A total of nine single nucleotide polymorphisms (SNPs) in <i>MAOA</i> gene were genotyped, of which six SNPs had significant differences (<i>p</i> &lt; 0.05) in allele frequency between the aggressive and docile pigs. Linkage disequilibrium and association analyses showed that the pigs inherited the wild genotypes showed more aggressive behavior (<i>p</i> &lt; 0.05) than pigs with the mutant genotypes of the four linked SNPs, rs321936011, rs331624976, rs346245147, and rs346324437. In addition, pigs of GCAA haplotype were more (<i>p</i> &lt; 0.05) aggressive than the pigs with GCGA or ATGG haplotype. The construct containing the wild genotype GG of rs321936011 had lower (<i>p</i> = 0.031) promoter activity compared to the mutant genotype AA. These results suggest that the four linked SNPs in <i>MAOA</i> gene could be considered as a molecular marker for behavioral trait selection in pigs.