Poultry production is an important agricultural sector for human food worldwide. Chicks after hatch often face health problems leading to economical losses that are deleterious for breeders. Avian β-defensin 2 (AvBD2) is a prominent host defense peptide of the intestinal mucosa of caecum and is involved in the resistance of poultry to bacterial pathogens. This peptide could thus represent an innate immunity marker of robustness of birds. To test this hypothesis by comparing fast-growing and slow-growing lines in different conditions of breeding, the chick’s caecal AvBD2 content was analysed according to robustness indicators. Chick’s caecal tissue sections labelled by immuno-histo-chemistry with specific antibodies revealed the unexpected localization of AvBD2 in the mucosa with high individual variability, without showing differences attributable to quality indicators, but interestingly showing inverse correlation with plasma IgM levels in the fast-growing line. The availability of our anti-AvBD2 antibodies to the scientific community opens perspectives to identify the cellular sources of this defensin in the caecal mucosa and to investigate the organisation and function of innate immune arsenal of birds.