Intestinal digestive enzyme modulation in house sparrow nestlings occurs within 24 h of a change in diet composition.

Nestling house sparrows near fledging age (12 days) were previously found to reversibly modulate the activity of their intestinal digestive enzymes in response to changes in diet composition. However, it is not known how quickly nestlings can adjust to new diets with different substrate compositions, nor is it known how early in life nestlings can modulate their enzyme activity in response to changes in diet. In the present study, 3-day-old nestlings were captured from the wild and fed and switched among contrasting diets - one high in protein and low in carbohydrate and another higher in carbohydrate and with lower, but adequate, protein - in order to determine (1) how quickly house sparrow nestlings could adjust to changes in diet composition, (2) how early in life nestlings could modulate their digestive enzyme activity in response to these changes and (3) which digestive enzymes could be modulated in house sparrow nestlings earlier in life. We found that house sparrow nestlings as young as 3 days post-hatch were capable of modulating their intestinal disaccharidase activity within 24 h of a change in diet composition, and nestlings gained the ability to modulate aminopeptidase-N by 6 or 7 days of age. To our knowledge, this is the first evidence of digestive enzyme modulation completed within 24 h of a change in diet in an avian species and the first study to show intestinal digestive enzyme modulation in response to changes in diet composition in any animal this early in development.