The relationship between the dwarfing gene and E. coli infection in two populations of chickens

Resistance to an E. coli challenge was studied in the 6th, 7th, and 8th backcross generations after the introduction of the sex-linked recessive dwarf gene (dw) into two populations of White Plymouth Rock chickens that had undergone bidirectional selection for juvenile body weight. In the B6 and B8 generations, the dwarf genotype from the HW line had significantly higher mortality and/or heart lesions than the heterozygotes while the homozygous normal chickens were intermediate. No association between the dwarf allele and the incidence of E. coli infection was observed in the HW line in any generation, but genotypes in the LW lines were influenced by social environment in susceptibility to the E. coli challenge. Under low social strife, the dwarf and heterozygote genotypes were more susceptible than the normal genotype to the E. coli challenge, while under a high social strife there were no differences among genotypes. Since the genotypes in the LW line responded differently to the disease challenge than those in the HW line, it was concluded that a line-dwarf genotype interaction was present.