Although much of the QTL-based mapping of the SAL1 locus in inbred lines used intravenous infection of day old chicks with S. Typhimurium, the phenotype of resistance to experimental fowl typhoid is strongly expressed in older birds (Bumstead and Barrow, 1993) with quantitative differences of 3–4 Log10 CFU per gram of liver tissue between resistant and susceptible lines found 8 days after oral challenge with S. Gallinarum in 3-week-old birds (Wigley et al., 2002). This evidence concerns the gene SALL1 and infection.