Effects of feeding a carboxypeptidase inhibitor from potatoes to newly hatched chicks.

For the first time, the effects on animal growth and protein digestion of a specific inhibitor of the pancreatic digestive exopeptidases carboxypeptidases A and B were studied. Carboxypeptidase inhibitor from potato tubers was fed to newly hatched chicks at a level equal to that present in a diet containing 50% raw potato solids, which was severely growth depressing. At this level the effect of the carboxypeptidase inhibitor on growth was insignificant but the following effects were noted: (1) increased fecal protein (the increase mainly consisting of low-molecular weight proteins); (b) poorer feed efficiency; and (c) a significant decrease in pancreatic digestive proenzyme levels, although no hypertrophy was noted. In addition, the inhibitor was not digested readily in the intestinal tract and increased in concentration in intestinal contents as it progressed down the tract. Potato Inhibitor II, a potent trypsin inhibitor, when fed to chicks, also at the level found in the diet containing 50% raw potato, was severely growth depressing. The inhibitor produced significantly increased fecal protein and caused pronounced pancreatic hypertrophy. Thus, the growth depressing effects of raw potato tubers is probably due in part to the trypsin inhibitor, with only a small contribution originating from the carboxypeptidase inhibitor.