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Pancreatic exocrine secretion in steers infused postruminally with casein and cornstarch^1,2

C. J. Richards^*,3, K. C. Swanson^*,4, S. J. Paton^*,5, D. L. Harmon^*,6 and G. B. Huntington

^* Department of Animal Sciences, University of Kentucky, Lexington 40546-0215 and and Department of Animal Sciences, North Carolina State University, Raleigh 27695-7621

⁶ Correspondence:
814 W.P. Garrigus Bldg. (phone: 859-257-7516; fax: 859-257-3412; E-mail:
dharmon{at}uky.edu).

Our objective was to evaluate the effect of postruminal protein infusion on pancreatic exocrine secretions. One Holstein, two crossbred, and five Angus steers (305 ± 5 kg) with pancreatic pouch-duodenal reentrant cannulas and abomasal infusion catheters were used in a replicated 4 x 4 Latin square. All steers were abomasally infused with 1,050 g/d of raw cornstarch with treatments of 0, 60, 120, or 180 g/d of sodium casein suspended in water to yield 6,000 g/d of infusate daily. Steers were limit-fed (1.5 x NE_m; 12 equal portions daily) a 90% corn silage, 10% supplement diet formulated to contain 12.5% CP. Periods consisted of 3 d of adaptation to infusion, 7 d of full infusion, 1 d of collection, and 7 d of rest. Pancreatic juice was collected in 30-min fractions continuously for 6 h. Total juice secreted and the pH of individual fractions were recorded, a 10% subsample was retained to form a composite sample, and remaining fluid was returned to the duodenum. Juice composite samples were stored (-30°C) until analyzed for total protein and activities of -amylase, trypsin, and chymotrypsin. Casein infusion linearly increased -amylase concentration (182 to 271 units/mL; P < 0.02; 17.5 to 24.6 units/mg of protein; P < 0.03) and secretion rate (26,847 to 41,894 units/h; P < 0.01). Total juice secretion (155 g/h), pH of pancreatic juice (8.13), secretion rate of protein (1,536 mg/h), and concentration of protein (10.2 mg/mL) in pancreatic secretions were not affected (P > 0.05) by casein infusion. Similarly, casein infusion did not change (P > 0.05) trypsin and chymotrypsin concentrations (1,379 and 349 units/L or 0.134 and 0.033 units/mg of protein, respectively) or secretion rates (206 and 52 units/h, respectively). Abomasal infusion of protein with starch stimulated a greater pancreatic secretion of -amylase activity into the intestine than infusion of starch alone.

Key Words: -Amylase • Beef Cattle • Pancreas • Protein Digestion • Ruminants • Starch Digestion

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