Chickens at the time of hatching, all systems are complete from the anatomical point of view, but from the standpoint of histological and functional, many of these systems are immature and should finish ripening at different life stages. These stages are determined in nature by climatic cycles and food availability, but factory farming is necessary to ripen them quickly to achieve maximum expression of genetic potential for growth.

Among the most critical systems are: digestive system (intestinal villi to shorten the small intestine and pancreas presented an allometric growth of 400% compared to the poultry carcass in the first 23 days of life, while the liver increased by 200%), and the immune system (stimulation of the immune response, increasing the number of intraepithelial lymphocytes, plasma cells and Peyer's patches).

The proper maturation of these systems must in the first 10 days of life of the chickens the following objectives:

– sixfold initial body weight may be influenced by the initial weight of the chicken and which in turn affects the final weight of the bird.

– Achieve and maintain a good uniformity (minimum 80%).

– Keep mortality below 1%.

– Yolk sac completely absorbed completely by the end of the first week of age.

The gastrointestinal tract is a tubular structure lined on the inside of epithelial cells constitute a selective barrier between the lumen and the so-called bird's body and perform various functions on its own and in collaboration with other digestive organs such as pancreas and liver, such as:

1. Convert complex molecules contained in food into simple molecules by hydrochloric acid secretion and intestinal enzymes, pancreatic and liver

2. Allows the passage of simple molecules (nutrients) by enterocytes

3. Prevent the passage of infectious agents from the yolk and food means immune elimination mechanisms (neutrophils, macrophages, mast cells)

4. Prevent the passage of infectious agents by specific immune mechanisms of exclusion (IgA and IgM)

Enterocytes are the basic cells of the epithelium and villi are grouped forming and in turn each has folds called microvilli. The aim of these villi and microvilli is to increase the surface contact with the food and lack of development (maturity) or shortening (pathology) causes severe losses in growth and food utilization.

For the birds express their genetic potential is necessary to accelerate the maturation of the intestinal mucosa and prevent attacks that may damage it.

Recent research on pronutrients permitted to use substances contained in plant extracts (malvidin, ellagic acid, jam, Connesina, embelica acid, alpha sulfurallin) to improve maturation of enterocytes, lymphocytes, stimulating the secretion of immunoglobulins and maintain regeneration cycles every 4 days of the gastrointestinal mucosa.

On the other hand the use of antioxidants, enzymes, mycotoxin binders, natural phenolic bactericide and fungicide and probiotics will avoid the damage on the gastrointestinal mucosa, by peroxidized fats, phytates, other than the starch polysaccharides, mycotoxins and biogenic amines, bacteria , protozoa, fungi, high viscosity diets.

The use of multifunctional additives can stimulate maturation and regeneration of the gastrointestinal mucosa, hepatocytes and immune cells of the intestine play a major role in growth and prevent chemical and biological agents that affect the status of the gastrointestinal mucosa.