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Abstract
The onset of feeding broiler chicks after hatch is often delayed by 48–72 hours due to variations in hatching time and follow up hatchery practices, affecting their ultimate performance at marketable age. In the newly hatched chicks, residual yolk serves as a source of nutrients until access to exogenous sources of feed is established. However, despite the residual yolk being sufficient to maintain the chicks during the first three to four days of life, it does not provide the required level of nutrients to fully support the genetic expression of the bird's potential for growth, development of the gastro-intestinal tract or the immune system. Development of the avian immune system is triggered during embryogenesis, but is not evolved until a few weeks of age post hatch, and can be stunted due to the unavailability of nutrients if hatchlings are deprived of food immediately after hatch. Early feeding is not only associated with immune organ development, but also with the functioning of the immune system in broiler hatchlings. With the continued increase in the economic importance of broiler chickens, an understanding of the development and function of the immune system in these birds and their capacity to respond effectively to divergent antigens is necessary.
