Itallo Conrado Sousa Araujo, R. Molenaar, A. Lammers, Henry van den Brand
The effect of day-old chick quality on health, welfare, and performance remains ambiguous in the scientific literature. This chapter reviews chick quality from three complementary perspectives: physical, immunological, and microbiological. Physical quality is traditionally evaluated using quantitative measures (e.g. chick weight, length) and qualitative scoring systems (Pasgar, Tona), which mainly reflect incubation conditions but show limited predictive value for long-term performance. Immunological quality is largely determined by maternal antibody transfer, especially IgY, which provides passive protection during the critical early post-hatch period. Microbiological quality, while less studied, is increasingly recognized as a determinant of chick viability. Vertical and horizontal transmission of microorganisms, eggshell contamination, and hatchery hygiene strongly affect early colonization of the gut microbiota, with consequences for health and resilience. Together, these perspectives illustrate that chick quality is a multifactorial concept, strongly influenced by breeder, egg, and hatchery factors, and its assessment should go beyond simple physical traits.