Enzyme activity and organ development in newly hatched chicks selected for high or low eight-week body weight

Cockerels from lines of White Plymouth Rock chickens selected for 33 generations for high (HW) or low (LW) 8-wk BW were used in this experiment. Either Diet A (a diet similar to that under which selection had been conducted) or Diet B (containing 20% more CP and 20% more ME) were consumed ad libitum for the entire experiment (hatch to 6 wk of age). Body weights, organ weights, and enzymes present in the gastrointestinal tract (GIT) contents and pancreas were measured. There were differences between lines and between diets for BW and relative breast weight. Several organs (heart, lung, liver, and pancreas) generally remained a constant proportion of BW in both lines. Relative weight of the GIT was greater in HW cockerels from hatch to 10 d of age, after which relative GIT weight was greater in LW cockerels. Relative weight of the GIT was also affected after 10 d of age by density of feed. Interactions between line and diet were present for many digestive enzyme measurements, necessitating analyses within each main effect. All pancreatic enzymes except relative trypsin were higher in HW than LW cockerels. Although small intestine enzyme activities were higher in Line HW than LW, Cockerels on a relative basis the difference was present only for trypsin activity. Cockerels fed Diet B had higher levels of pancreatic chymotrypsin activity and of total and relative lipase activities than those fed Diet A.