Energy utilization in newly hatched chicks.

The changes in body weight and composition were examined in broilers that either had immediate access to feed and water or had not been fed for 48 h posthatch. Chicks without access to feed decreased in BW by 7.8% in the 48 h posthatch, which was equivalent to 5.3 kcal/45 g chick/d. However, during this period the small intestines increased in weight and protein content by 80% or more. The decrease in yolk fat and protein could account for most of the changes in body composition in the feed-deprived chick. In contrast, fed chicks grew by 5 g and used 4.5 kcal/d for maintenance; during this period small intestines increased in weight by 110%. Intestinal absorption of exogenous nutrients was determined from hatch through 4 d posthatch by administration of a bolus of labeled glucose, methionine, or oleic acid, together with a nonabsorbed reference substance. Absorption of fatty acids was more than 80% at hatch and was higher than that of glucose and methionine, which was low especially when the bolus was administered as a solution. Absorption of all components tested increased with age and was more than 80% on Day 4. Duodenal in situ uptake determinations in hatching chicks indicated that uptake of oleic acid was high from yolk and saline solutions compared with glucose and methionine, which exhibited low uptake from yolk but higher uptake from saline solutions. These studies indicate that, although the small intestine has the capacity to absorb carbohydrates and amino acids at hatch, uptake may be dependant on the development of suitable conditions, including sufficient pancreatic and brush border enzymes for digestion and adequate sodium for function of the glucose-sodium cotransporters.