Concurrent studies of the flow of digesta in the duodenum and of exocrine pancreatic secretion of calves

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Abstract
1. The effect of age on the flow of duodenal digesta and of pancreatic secretion was studied in preruminant calves fitted with duodenal re-entrant and pancreatic sac cannulas. In Expt 1 a comparison was made at 7, 24 and 63 d of age of Ayrshire calves given whole milk, and in Expt 2 Friesian calves given milk-substitute diets were studied during the period 16–37 d of age.2. For the Ayrshire calves, ad lib. whole-milk intake increased with age, but whole-milk intake on a per kg metabolic body-weight (W0.75) basis did not alter. As the intake increased with age, the whey fluids were passed out of the abomasum more rapidly.3. As judged by the mean duodenal pH values and the values for ‘chloride ion minus sodium ion’ concentration in the digesta, and for apparent secretions (total quantity recovered at duodenal cannula during 12 h after feeding minus intake) the duodenal digesta became more acid as the Ayrshire calves became older. There was no change with age in the extent of degradation of the milk proteins as indicated by the protein-nitrogen: total N values for duodenal digesta.4. The volume of pancreatic fluids secreted by the Ayrshire calves increased markedly with age, but when expressed on a per kg W0.75 the volume did not increase after 24 d of age. In absolute terms and also in relation to whole-milk intake or W0.75 there was a large increase in secretion of total protease, a very large increase in α-amylase (EC 3.2.1.1) but no change in trypsin (EC 3.4.4.4) activities with age.5. In the Friesian calves secretion of pancreatic fluid and activities of α-chymotrypsin (EC 3.4.4.5), α-amylase, lipase (EC 3.1.1.3) and ribonuclease (EC 2.7.7.16, 2.7.7.17) but not trypsin or total protease increased with age.6. The extent of the increase in secretion of pancreatic enzymes during the first hour after the Friesian calves were fed milk-substitute diets differed between enzymes.7. The changes in the quantities of pancreatic enzymes secreted are discussed in relation to the changes in the digestibility of milk-substitute diets.

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