Hydrolysis and absorption in the small intestines of posthatch chicks.

In the immediate posthatch period, chicks must transfer from metabolic dependence on yolk to utilization of exogenous feed. This study describes changes in intestinal luminal pancreatic enzyme activity and mucosal uptake posthatch as influenced by feed and Na intake. Chicks with access to feed increased in BW and small intestinal weight in the 48-h posthatch, whereas chicks without access to feed decreased in BW; however, small intestinal weight increased during this period. Chicks ingesting feed showed increases in total intestinal trypsin, amylase and lipase activities that were correlated with intestinal weights and BW. Chicks without access to feed showed little change in trypsin and amylase activities, and these increased only after feed consumption. Feeding a low-Na diet did not significantly change the regression coefficient between pancreatic enzyme activity and BW. Mucosal uptake was estimated by measuring Na+,K+-adenosine triphosphatase (ATPase) activity in small intestinal segments. In fed birds this activity increased in relationship to growth, whereas in nonfed birds uptake increased only after access to feed. Low-Na diets allowed only minimal mucosal uptake in all intestinal segments. This study indicates that secretion of trypsin and amylase into the intestine was triggered by feed intake. In addition, Na plays a critical role in intestinal uptake in the immediate posthatch period.