The research on factors influencing on cholesterol synthesis in chickens and egg cholesterol contents

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Egg contains a relatively high cholesterol content. It would be economically advantageous for egg producer to be able to provide a low cholesterol egg and many research efforts have been directed toward this goal. The liver is the primary sites of cholesterol biosynthesis in laying hens. However, intestinal mucosa has been demonstrated to be second only to liver as a source of endogenously synthesized cholesterol. The present investigation was designed to study the effect of different type of dietary fats on cholesterol biosynthesis through HMG-CoA reductase activity in the intestinal mucosa, as well as the liver of growing chicks (Experiment 1 and 2). Furthermore, this enzyme activity was compared laying with non-laying hens (Experiment 3). In experment 1, the hepatic HMG-CoA reductase activity showed the highest value in chicks fed the tallow-containing diet. Chicks fed diets containing safflower or coconut oil resulted in a significantly lower intestinal HMG-CoA reductase activity in comparison with those fed the olive oil-containing diet. In experiment 2, the hepatic HMG-CoA reductase activity was significantly higher when fat-free and trilaurin were fed than when any other triglycerides were fed. This activity showed the lowest value in the chicks fed the diet containing tristearin. The HMG-CoA reductase activities in the jejunum and ileum were significantly or tended to be higher when trilaurin was fed than when any other triglycerides were fed. Except when trilaurin was fed, the presence of saturated fat in the diet did not have a significant effect on the intestinal HMG-CoA reductase activity, unlike the effect shown when a highly unsaturated fat was added to the diet. There was no significant correlation between the HMG-CoA reductase activities of the liver and intestine, and this enzyme activity and cholesterol content of intestinal epithelial cells. In Experiment 3, the hepatic HMG-CoA reductase activity in laying hens was significantly higher than those