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Investigation of polymorphisms at the MUC4, MUC13, MUC20 and TFRC candidate genes for F4ab/ac resistance in South African pig populations
Selection for E. coli F4ab/ac resistance has become common due to the increasing resistance of the bacteria to antibiotics. Four candidate genes were studied in three South African breeds, Exotic (Large White, Landrace and Duroc), indigenous and crossbred (Exotic x indigenous), in order to identify polymorphisms conferring resistance to E. coli F4ab/ac. A total of 225 pigs aged 3-12 weeks were genotyped to target restriction sites in MUC4, MUC13, MUC20 and TFRC candidate genes. Four polymorphisms of c.8227G>C for MUC4, c.576C>T for MUC13, g.191C>T for MUC20 and c.291C>T for TFRC were detected. The susceptible allele C was close to fixation at over 90 % in all three breeds for the TFRC and MUC13 loci and there was a genic and genotypic significant difference (P < 0.05) amongst breeds for the TFRC loci. The resistant TT genotype was found in less than 2 % of the entire population for the TFRC locus and was not found in any pigs for the MUC13 locus. Both TFRC and MUC13 were not polymorphic in the studied population. The MUC4 and MUC20 genes were polymorphic in the population. The resistant alleles G for MUC4 and C for MUC20 were present in the population with the highest frequency observed in the Exotic pigs. There was a significant difference in genotypic distribution amongst breeds at the MUC20 and MUC4 loci (P <0.05). An excess of homozygotes in TFRC and MUC20 was observed, leading to a deviation from HWE in the Exotic pigs at these loci. All three breeds were in HWE at the MUC4 loci although an excess in heterozygotes was observed. The subpopulations at the TFRC, MUC13 and MUC20 loci were inbred and those at the MUC4 locus were outbred. There was no significant linkage disequilibrium observed amongst the loci analysed. The results showed that MUC4 and MUC20 were informative and the presence of the resistant alleles makes it possible to use them as markers for selection against susceptibility to F4 E. coli.
Keywords:
Pigs, polymorphisms, E. coli F4