The importance of lipolytic enzymes in milk-fed and ruminating calves

Abstract

An attempt has been made to compare the activity and specificity of pregastric esterase and pancreatic lipase from calves 1-2 weeks of age in an in vitro system using washed milk-fat globules as substrate. In addition, the changes in activity of pancreatic lipase and pancreatic phospholipase have been investigated as milk-fed calves change from a monogastric to a ruminant type of digestion. The results showed that pregastric esterase and pancreatic lipase have a similar specificity for long-chain fatty acids in milk triglyceride, and that on a unit volume basis the activity of pregastric esterase is approximately 10 times lower than that of pancreatic lipase. In the absence of pancreatic juice, pregastric esterase activity in the duodenum of milk-fed calves was negligible. The lipase activity per unit volume of pancreatic juice from 2-day-old calves was not significantly greater than that from 2- week-old calves. However, there was a substantial increase in flow in the latter calves, resulting in a threefold increase in the output of pancreatic lipase activity per kilogram body weight. In ruminant calves (6-7 months old) there was a further threefold increase in output of pancreatic lipase per kilogram body weight. The conversion oflecithin to lysolecithin occurred much more rapidly in intestinal contents of ruminating calves compared with 1-2-week-old calves, although in vitro studies revealed that there was a rapid conversion using pancreatic juice and bile from both groups of calves at pH 7'5 and 6'2, but not at pH 5.2. The addition of large quantities of milk triglyceride to incubation mixtures containing pancreatic juice and bile from calves 1-2 weeks of age substantially inhibited the conversion of lecithin to lysolecithin. Inactivation of pancreatic lipase from ruminating and young calves resulted in a large reduction in the hydrolysis of biliary lecithin in vitro. Evidence presented suggests that pancreatic lipase is the major enzyme involved in hydrolysis of lecithin and that conditions of low pH or the presence of triglyceride inhibit this reaction. © 1973 CSIRO.