Ontogenetic development of gut function, growth, and metabolism in a wild bird, the Red Jungle Fowl.

We measured the ontogeny of growth rate, food intake, metabolic rates, organ masses, and intestinal nutrient transporter and hydrolase activities in a wild bird for comparison with previous measurements of the same quantities in four domesticated or laboratory animals. Analysis of covariance with body mass as a covariate showed that body mass accounted for most of the age-related variation in all variables, but that age itself still had a significant effect on most variables. Among organs studied, the ceca exhibited the greatest mass increase with age. Energy intake and resting and basal metabolic rates increased with age, but digestive efficiency, cost of growth, and sustained metabolic scope were independent of age. Although intestinal brush-border glucose and proline uptakes and sucrase activity declined with age, the corresponding capacities increased with age because of compensating increases in intestinal mass. Intestinal passive permeability to glucose was undetectably low. Unlike the four domesticated animals studied to date, jungle fowl possess no intestinal reserve capacities (excesses of capacity over dietary nutrient intake). Cecal absorption may contribute significantly to glucose uptake capacity with increasing age.