Postruminal administration of partially hydrolyzed starch and casein influences pancreatic alpha-amylase expression in calves.

The objective was to examine the effects of postruminal partially hydrolyzed starch (SH) and/or casein on the expression of pancreatic alpha-amylase mRNA, protein and activity in calves. Holstein calves [(n = 24) 88 plus minus 3 kg body weight (BW)], fitted with abomasal infusion cannulas, were randomly assigned within block (week of infusion) to one of four abomasal infusion treatments. Calves were fed an alfalfa-based diet, and SH [4 g/(kg BW.d)] and/or casein [0.6 g/(kg BW.d)] was infused abomasally for 10 d before tissue collection. There was a SH x casein interaction (P < 0.10) for pancreatic weight (g and g/kg BW) because casein increased pancreatic weight in the absence of SH but did not influence pancreatic weight in the presence of SH. Pancreatic alpha-amylase mRNA tended to be lower (P = 0.06) and protein and activity (U/g pancreas and U/g protein) were lower (P = 0.02) in calves receiving abomasal SH. The concentration of pancreatic trypsin activity (U/g pancreas and U/g protein) was lower (P < 0.03) in calves receiving abomasal SH. There was a SH x casein interaction for total alpha-amylase and trypsin activity [U/pancreas and U/(pancreas.kg BW)] because casein increased total activity in the absence of SH but not in the presence of SH. These data suggest that increases in small intestinal protein flow enhance pancreatic weight and thus total pancreatic alpha-amylase and trypsin activity, yet small intestinal SH inhibits the increase in pancreatic weight resulting from increased small intestinal protein flow. Additionally, postruminal SH decreases alpha-amylase expression largely by translational events.