Physiological Basis of Early Life Nutrition in Chickens

The transitions from late embryonic development through hatching and on through the first two weeks of post-hatch growth represent a period of tremendous changes in the gastrointestinal tract and nutrient metabolism in chickens. During late embryonic development, the principle metabolic pathways in the liver center around lipolytic and gluconeogenic metabolism. Immediately after hatching, hepatic metabolism shifts to glycolytic and lipogenic metabolism. This metabolic transition is evidenced by massive changes in expression of genes related to lipolysis, lipogenesis, glycolysis, and ketogenesis. Similar changes occur in other tissues, including adipose tissue and skeletal muscle. Concurrent with these dramatic changes in nutrient metabolism, the gastrointestinal tract undergoes substantial changes, including growth and functional maturation. One such example is growth of the small intestine, which increases three-fold in length during the final days of embryonic development and another seven- to ten-fold during the first two weeks after hatch. Similarly, villus height and number increase from late embryonic development through the first one to two weeks after hatch. These changes in the anatomy, physiology, and metabolism during early life development of the chick alter nutrient absorption and utilization. Similarly, feed and its formulation alter physiological systems related to feed intake, body growth, and nutrient metabolism. The transition from lipolytic to lipogenic metabolism at hatching is delayed when initial access to feed is delayed. Similarly, ontogenic profiles of pathways in skeletal muscle related to protein accretion and fiber growth are delayed in response to delayed feeding. Within the hypothalamus of the brain, pathways regulating appetite and satiety and whole-body metabolic rate are affected by delayed feeding. Most but not all of the gene expression patterns in these pathways revert to their normal level after the birds are provided feed. In other words, access to feed induces the remarkable changes in physiology and metabolism that occur at hatching. However, despite nearly two decades of research in this area, the specific components within feed responsible for functional changes in tissues as disparate as the liver, skeletal muscle, adipose tissue, and the hypothalamus remain unknown. A collaborative effort by nutritionists and physiologists at the molecular and genomics levels is necessary to elucidate the underlying mechanisms regulating the functional changes that occur in multiple organ systems from late embryonic development through the first two weeks of post-hatch growth. These functional changes in multiple organs affect early life nutrient absorption, metabolism, and utilization.

Presented at the 34th Annual Australian Poultry Science Symposium 2023. For information on the next edition, click here.