Broiler Breeding: Small Intestine Development and Nutrient Absorption

Broiler Breeding: Small Intestine Development and Nutrient Absorption

Further understanding of the physiological function of the small intestine in broilers is indispensable for practitioners. How does the small intestine develop at different ages? When is the growth of intestinal villi complete? Does the gut require the same amount of nutrients at different ages? Only the fittest, breeding will have a lower risk. 

Effect of age on intestinal development

Picture from https://ab-neo.com/industry/poultry/gut-health

The small intestine grows rapidly in the late hatching period, accounting for 1% of the body weight on the 17th day of hatching to 3.5% of the body weight on the 21st day of hatching. The intestinal length increases 2 to 4 times within 12 days after hatching. The length of the villi increases near hatching, and the size and number of villi increase after hatching.

The growth of duodenal villi was nearly complete on the 7th day after hatchling, but the growth of jejunum and ileum villi lasted until 14 days after hatchling. Unlike mammalian intestinal cell proliferation, which mostly occurs in crypts, avian intestinal cell proliferation can occur throughout the villi. It takes 3 days for intestinal cells to migrate to the apex of villi in 4-day-old chicks and 4 days for older chicks.

Postnatal growth rate is at least partially influenced by the allometric growth of various organs. The intestinal tract grows rapidly after hatching, with the fastest relative growth rate at 5 to 7 days of age. At 12 days of age, the length of the intestine increases 2 to 4 times, and the small intestine increases 7 to 10 times during this period.

Effect of age on nutrient absorption

As far as the activity of intestinal trypsin is concerned, the activities of trypsin, protease and amylase in the small intestine increase rapidly within 21 days after hatching. However, lipase activity began to increase after 21 days of age. Feeding high-fat feed before 21 days of age does not significantly increase lipase activity. Lipase activity appears to be the limiting factor affecting digestion, at least during the first few weeks.

During the development of broiler chickens, a series of significant changes occur in the development of the nutrient transport system. During the first week after hatching, the uptake of proline in the small intestine is higher than the uptake of glucose. Since the relative growth rate of broilers is highest in week 1, amino acid absorption matches this growth pattern.

Glucose uptake increases transiently during the 2nd week. It is hypothesized that this increase is the result of a switch from lipid to carbohydrate metabolism in broilers due to depletion of yolk reserves. Due to the allometric growth of the intestine, the weight of the intestine as a proportion of the body weight decreases during the second week after hatching, which may be a second reason for the increased glucose intake during this period. There was a transient increase in proline uptake at week 6, an increase that coincided with the first post-larval moult and an increase in absolute growth rate.

The intestinal absorptive capacity of broiler chickens is consistent with their nutritional requirements. This contrasts with results in mammals, which consume far more than their requirements. It remains to be elucidated whether nutrient uptake is a potential limitation to broiler growth or whether broilers are better able to allocate nutritional resources.

Feeding immediately after hatching stimulates intestinal development. Delayed feeding for 24 to 48h reduced villi length, intestinal cell migration rate and intestinal cell number, but increased the number of goblet cells that produced acid and neutral mucus.

At present, commercial broilers will be prepared in advance on the day of replenishment. Water and feed are provided at the same time to ensure that the chicks can drink water and eat food immediately after entering the house. The satiety rate of the chicks within 12 hours is observed. The satiety rate is a very important production indicator to judge whether the chicks are healthy and whether the chicken house environment is suitable.

 Picture from foodservicefootprint.com

Chicks have a high demand for nutrients, and if the growth of other organs is too fast, it may lead to incomplete development of the small intestine, which affects the digestion and absorption function. This phenomenon is particularly prominent in intensive farming, which is often affected by limiting factors such as space, feed quality and stress response, further inhibiting the normal growth of the small intestine. By introducing bioactive peptides as feed additives, these adverse effects can be effectively alleviated and the healthy development of small intestine and other organs can be promoted.