Effect of age and exogenous amylase and protease on development of the digestive tract, pancreatic enzyme activities and digestibility of nutrients in young meat-type chicks.

Day-old male meat-type chicks were fed a commercial starter diet supplemented with 2 levels of enzyme preparations containing amylase and proteases up to 14 d of age. Enzyme supplementation had no significant effect on feed intake or growth rate, and was accompanied by a significant decrease in gizzard content and small intestine weight. The intestine contents increased and this increase was accompanied by a significant decrease in its pH. Enzyme supplementation depressed the activity of chymotrypsin in the pancreas and the activity of amylase, trypsin and chymotrypsin in the intestinal contents. Some carry-over effects were observed on d 42, 4 weeks after the cessation of the enzyme supplements. These were mainly a significant depression in the activity of trypsin in the intestinal contents. In a balance study, diets supplemented with 0,250 and 1,000 micrograms/kg enzyme preparations were supplied. Exogenous enzyme supplements had no significant effect on the digestibility of all the nutrients studied except for the highest level of enzyme supplementation, which improved slightly but consistently the digestibility of amino acids. Some age effects were observed, mainly a decrease in the digestibility of fat and starch, and in the ME of the diet from weeks 1 to 2 followed by an increase during week 3. Protein digestibility and retention of nitrogen decreased with age.