UBC Theses and Dissertations
Dietary lipid factors influencing sterol and fatty acid metabolism in laying hens Sim, Jeong Seok
Two feeding trials were conducted with 30-week-old single comb white leghorns fed two basal diets containing 8% of hydrogenated coconut oil or safflower oil. These basal diets were fed with or without supplements of \% cholesterol (ch), 2-fo soysterols (st) or in combination (ch+st). Trial 1 was designed to study the sensitivity of laying hens in response to dietary lipid factors and to compare the mode of changes in serum and egg yolk concentrations by weekly determination of their sterol levels during a feeding period with no soysterol supplementation followed by a period with soysterol supplementation. Objectives of trial 2 were to study the effects of dietary lipid factors on the serum and egg yolk levels and to delineate their roles or mechanisms. Changes in egg yolk sterol levels caused by dietary lipid factors were generally parallel to, and preceded by, those in serum sterol levels. This indicated that the egg sterols originated from the circulating labile sterol pool. Safflower oil suppressed and hydrogenated coconut oil elevated the sterol levels in both serum and egg yolk. Cholesterol feeding with dietary safflower oil increased the absorption of cholesterol, resulting in an increase of serum and egg sterol levels as compared to sterol levels of hens fed Hydrogenated coconut oil. Dietary soysterols supplementation resulted in a decrease in both serum and egg yolk sterols which was demonstrated in the presence of dietary cholesterol as well as cholesterol-free treatments. The apparent absorption of cholesterol was not retarded by the simultaneous feeding of cholesterol and soysterols. However, soysterol feeding accelerated the fecal excretion of bile acids and catabolic products of neutral sterols. The apparent absorption of plant sterols was 11%. Absorbability Of plant sterols in laying hens was further supported by detection of these sterols in tissue and egg yolk. The absorption of the plant sterols was, however,. Slightly decreased when cholesterol was fed simultaneously. Cholesterol feeding increased total lipid content in liver and serum, whereas soysterol feeding reduced or diminished lipid accumulation caused by the cholesterol treatment. Both dietary cholesterol and soysterols altered the fatty acid composition of liver, serum and egg yolk lipids by increasing oleic acid and decreasing palmitic and/or stearic acids. These changes were significantly greater upon feeding cholesterol than soysterols. However, the simultaneous feeding of cholesterol with soysterols exerted the least effect on the fatty acid composition in liver. The possibility that soysterols affected biosynthesis and/or oxidative catabolism of fatty acids in the liver of laying hens in a similar fashion as cholesterol was discussed.
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