Identification of Single Nucleotide Polymorphisms in Porcine MAOA Gene Associated with Aggressive Behavior of Weaned Pigs after Group Mixing.

Ruonan Chen,Qingpo Chu,Xinpeng Liu,Bo Zhou,Xian Tong,Siyuan Gao,Chunyan Shen,Allan P Schinckel

doi:10.3390/ani9110952

Abstract

Simple SummaryMonoamine Oxidase A (MAOA) gene had been reported as a candidate gene of aggressive behavior in several species. In the present study, the most aggressive and docile weaned pigs in each pen after group mixing were selected to identify single nucleotide polymorphisms in porcine MAOA gene associated with aggressive behavior. Constructs containing variable lengths of truncated porcine MAOA promoter were used to determine the promoter activity by a dual luciferase reporter system. The core promoter region of porcine MAOA was located at −679 bp to −400 bp. A total of nine single nucleotide polymorphisms (SNPs) in the MAOA gene were genotyped, of which six SNPs had significant differences in allele frequency between the aggressive and docile pigs. Four linked SNPs in porcine MAOA gene were associated with aggressive behavior in weaned pigs after mixing, which can be used as candidate molecular markers for aggressive behavior in pigs.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 (MAOA) gene is known as the “warrior” gene, as it has been previously linked to aggressive behavior in humans and livestock animals. To identify single nucleotide polymorphisms in porcine MAOA 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 MAOA promoter were used to determine the promoter activity by a dual luciferase reporter system. The core promoter region was located at −679 bp to −400 bp. A total of nine single nucleotide polymorphisms (SNPs) in MAOA gene were genotyped, of which six SNPs had significant differences (p < 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 (p < 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 (p < 0.05) aggressive than the pigs with GCGA or ATGG haplotype. The construct containing the wild genotype GG of rs321936011 had lower (p = 0.031) promoter activity compared to the mutant genotype AA. These results suggest that the four linked SNPs in MAOA gene could be considered as a molecular marker for behavioral trait selection in pigs.

Highlights

It is a common procedure that piglets are regrouped after weaning to create homogenous groups for equalizing competition in commercial pig farming [1]
We found that the aggressive behavior of pigs after group mixing was related to the genetic polymorphism of the monoamine oxidase A (MAOA) gene
The promoter activity analysis suggests that the core promoter region of the porcine MAOA gene is located between −679 bp and −400 bp from the initiation site of transcription

Summary

Introduction

It is a common procedure that piglets are regrouped after weaning to create homogenous groups for equalizing competition in commercial pig farming [1]. To reestablish a new social hierarchy, weaned pigs often show a high frequency of agonistic behavior after mixing [2]. Agonistic behavior of weaned pigs lasted approximately 4 days after mixing until a stable hierarchy had been established [3]. To reduce agonistic behavior of pigs, a number of practical interventions have been explored [1], but no clear economically effective solution has been identified. The heritability parameters of aggressive behavioral traits indicate that the visible expression of aggression is heritable in pigs [8]. Aggressive behavior could be reduced through genetic selection [9], which has been successively used in poultry [10]. Identification of molecular genetic markers associated with agonistic behavioral traits could contribute to optimize the genetic selection

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