Pancreatic Exocrine Secretion And Blood Parameters In Response To Graded Levels Of Duodenal Leucine Infusions In Cows

Starch is the main energy resource for ruminant. High-concentrate diets containing massive starch are used to meet the energy need of high-producing ruminant. There appears to be a considerable capacity for starch digestion in the small intestine of dairy cow, however, energy efficiency of starch digested in the intestine is42%higher than rumen. It is concluded that with increasing starch flow to the small intestine, the starch digestibility decreased. Greater starch flow from rumen, when the digestion of starch reaching the small intestine is limited, may lead to excessive carbohydrate fermentation in hindgut, resulting in energy waste, even damage to the animals. Thus, starch utilization in small intestine of ruminants must be optimized. Many factors limit starch digestion and lack of pancreatic α-amylase may be the main reason. It is known that leucine is the substrate for protein synthesis, as well as an efficient nutrient signal regulating protein synthesis. It is reported that leucine can down-regulated a-amylase activity and it mRNA expression in rats, but promotes secretion of α-amylase in goat. Thus indicating the possible differences between nonruminant and ruminant on leucine-induced effect on pancreatic secretion. Compared to goats, cows have even lower intestinal starch digestibility, which could only digest55%starch entered into the intestine. Therefore, the experiment was conducted to evaluate the effects of duodenal leucine infusion on pancreatic enzyme secretion, and plasma concentrations of some gastrointestinal hormones may be involved.Experiment1A method of real-time monitoring pancreatic exocrine secretion of dairy cowsSeveral Chinese Holstein cows (215±7kg) which were surgically prepared with a pancreatic pouch into which the main pancreatic duct drains, and two duodenal cannulas were used to establish method of real-time monitoring pancreatic exocrine secretion of dairy cows.The results showed that the method had high success rate, and was labour-saving, as well as work-efficient. It could be a way real-monitoring pancreatic exocrine secretion of dairy cow without damaging digestive system function of dairy cows.Experiment2Daily secretion patterns of pancreatic juice in dairy cowsFour Chinese Holstein cows (prepared procedures as exp.1) were used to record daily secretion patterns of pancreatic juice in cows. It was shown that the secretion rate of pancreatic juice was111.95±8.96mL/h (0.52mL·kg-1·h-1) under the current condition. According to the correlation analysis between feeding and secretion of pancreatic juice, feeding could increase pancreatic juice secretion significantly (P<0.05).Experiment3Pancreatic exocrine secretion and plasma parameters in response to graded levels of duodenal leucine infusions in cowsFour Chinese Holstein cows (prepared procedures as exp.1) were used in a4x4Latin square experiment to measure the effects of duodenal leucine infusions (0,10,20and30g) on pancreatic exocrine secretion and plasma parameters. Each period includes12-h infusion and36-h collection.The results showed that protein concentration (5.46±0.41mg/mL) was not altered among different groups. And no significant differences were found in the rate of protein secretion (673.92±53.84mg/h) and pH (7.24±0.04). Leucine infusion cubicly increased specific activity (U/mg; P<0.001) and the secretion rate of a-amylase activity (U/h; P<0.001) with the greatest value observed both at10g leucine. These changes corresponded to a cubic increase in the a-amylase concentration activity (U/mL; P<0.001) specific activity (U/mg; P<0.001), but reached its peak in30g leucine. Concentration (U/L; P<0.01) and the secretion rate (U/h; P<0.01) of chymotrypsin activity was regulated by leucine, which achieved the maximum value at30g and10g, respectively. In addition, specific activity (U/mg; P<0.001) of lipase had a peak value at lOg leucine.There were no significant effects on the pancreatic secretion of trypsin, as well as specific activity of chymotrypsin (U/mg), concentration activity (U/mL) and the secretion rate of lipase activity (U/h) by leucine infusions. Plasma glucose concentrations were also not significantly affected. However, infusions of leucine were reflected in the different plasma level of insulin (P<0.01). It is also indicated that infusion of leucine for12h stimulated the rate of a-amylase activity secretion linearly. However, there were no significant differences among treatments over the second12-h period. Both groups with0and10leucine infused previously had a dramatic increase in the rate, while other groups, especially the level of20g leucine, were nearly unchanged over25-36h.These data indicated that feeding could stimulate pancreatic exocrine secretion. Moreover, leucine could regulate pancreatic exocrine secretion, and there appeared to be the dose-effect relationship between them. Changes in hormones, such as insulin and cholecystokinin, may be involved in the changes in enzyme secretion.