EFFECT OF DIFFERENT FAT SOURCES ON CHOLESTEROL LEVELS OF YOLK AND BLOOD IN LAYERS

The cholesterol content of eggs is still part of the public discussion also it has been proved, meanwhile, that the cholesterol level in blood does not depend on the cholesterol intake with the food. Accordingly, now it is believed in human nutrition that the content of unsaturated fatty acids in the food is more important. High levels of polyunsaturated fatty acids, especially of the type omega-3, as well as wide ratios of polyunsaturated fatty acids (PUFA) to saturated acids are assessed positively concerning the prevention of atherosclerosis. In the present experiment it was intended to test to what extent the performance, the cholesterol levels in blood and in yolks of layers may be influenced by the use of fat sources in the diets differing in the composition of fatty acids. As fat sources coconut fat, tallow, standardised soyabean fat and see animal fat besides a positive control of soyabean oil were added to the diets. The diets were fed to 12 LSL layers each kept in single cages. The performance of the birds was recorded over one year and in the 2nd, 5th, 8th and 11th month of lay the cholesterol contents of the yolks were determined. In the 3rd and 9th month of lay blood was taken to determine the cholesterol level of the blood. Besides this, the fatty acid compositions of the diets and in the yolks were analysed. The fat sources in the diets did not effect the performance of the layers (laying performance, egg weights, feed consumption). The fatty acid compositions in the yolks agreed with the compositions in diets, but the differences in the yolks were not as distinct. The lowest cholesterol levels in yolks and blood were recorded for the diets with soyabean oil which showed the widest ratios of PUFAs to saturated fatty acids whereas the diet with coconut oil was most unfavourable. Further, it was registrated that the cholesterol levels of yolk and blood were decreasing with the age of the hens. The same was due to the HDL cholesterol fraction in the blood. Nevertheless, hens from the groups fed with soyabean oil showed the highest HDL values. Altogether, the achieved reduction in the cholesterol content of the eggs by using different fat sources were only low.