The present invention provides a method of identifying an animal having a genotype associated with resistance to bacterial infection comprising the steps of: (a) providing a sample from said mammal (b) determining the alleles at one or more markers of the SAL1 locus to identify the genotype of the marker, wherein said SAL1 locus lies between 54.0 MB to 54.8 MB of chicken Chromosome 5 or an equivalent thereof and (c) determining whether the genotype is a genotype associated with resistance to bacterial infection.
