Early development of small intestinal function

To accommodate the rapid transition to external nutrient sources, the chicken small intestine goes through morphological, cellular and molecular changes towards the end of incubation. The weight of the intestine, as a proportion of embryonic weight, increases from approximately 1% at 17 days of incubation (17E) to 3.5% at hatch. At this time, the embryonic small intestinal villi are divided into two main developmental stages, which differ in both length and shape. Mucin-producing cells can be observed from 17E and at that time contain only acidic mucin. The activity and RNA expression of brush-border enzymes, which digest disaccharides and small peptides, and of major transporters (sodium-glucose transporter and ATPase) which are found at 15E, begin to increase at 19E (2 days prior to hatch), and increase further on the day of hatch. Although the digestive capacity begins to develop a few days before hatch, most of the development occurs post-hatch when the neonatal chick begins consuming feed. During the post-hatch period, the weight of the small intestine increases at a faster rate than body mass. Rapid enterocyte proliferation and differentiation occur. In addition the intestinal crypts, which begin to form at hatch, are clearly defined several days post-hatch, increasing in both cell number and size. Goblet cells produce acidic and neutral mucins in similar proportions. Studies have shown that feeding immediately post-hatch or even pre-hatch accelerates the functional development of the small intestine, while delayed access to external feed arrests the development of the small intestine's mucosal layer and changes mucin dynamics.