Functional Development of the Small Intestine in Domestic Birds: Cellular and Molecular Aspects

The development of a functionally intact intestinal tract is essential for the successful production of poultry, particularly meat-type birds and turkeys. Yet, a paucity of information exists on the development of the small intestine, especially in newly hatched chicks and poults. Several criteria are used by our group for examining intestinal maturation and functional development of the small intestine. Among them are morphological studies, enterocyte proliferation, migration and turnover time, and the biochemical activity and RNA expression of brush-border enzymes. Our observations have documented rapid morphological development after hatching with differing rates of increase in villus volume in the duodenum, jejunum and ileum. When access to first feed is delayed, small intestinal development is slower. Proliferating cells are located in the crypt and up to the middle region of the villus, with the crypt region exhibiting a significantly higher number of proliferating cells. Different migration rates of enterocytes along the villi are observed in the three sections of the small intestine, with the highest rate in the duodenum and the lowest in the ileum. The brush-border enzyme activities differ in the three regions of the small intestine and are altered when first feeding is delayed or in vitamin A deficient diet. The use of cDNA probes detected the RNA expression of two brush-border enzymes. The understanding of molecular mechanisms regulating enterocyte proliferation and functional maturation will introduce a new dimension to poultry nutrition and will contribute to a better matching of the diet at an early age. Moreover, it will open a field of manipulations, administrated either by in-ovo treatments or in the first days after hatch, which will contribute to earlier development of the small intestine.