Effect of dietary conjugated linoleic acid on the fatty acid composi- tion of egg yolk, liver and adipose tissue in laying hens Einfluss von konjugierter Linolsäure auf das Fettsäuremuster des Dotters, der Leber und des Fettgewebes von Legehennen

The human health aspects of dietary fatty acids have been in the focus of nutritional studies. Several experiments have revealed that dietary conjugated linoleic acid (CLA) has anticancer activity, antiartherogenic effects, reduces body fat gain and enhances immune responses (PARIZA et al., 2000). The term CLA refers to a group of positional and geometric isomers of linoleic acid. The cis-9, trans-11 (c9,t11) and trans-10, cis-12 (t10,c12) isomers have been implicated as biologically active forms, showing the highest absorption and deposition rates (CHIN et al., 1992). Products of ruminants, like milk and meat are the main food sources of these isomers of CLA (CHIN et al., 1992; ). They can be produced in the forestomach of ruminants during microbial biohydrogenation of linoleic and α-linolenic acid (KEPLER and TOVE, 1967) or through the conversion of vaccenic acid (trans-11-C18:1) by δ-9 desaturase reaction in the mammary gland (GRIINARI et al., 2000). The synthesis of CLA may take place in the gastrointestinal tract and in other tissues of monogastric animals as well. It is the reason that CLA was measured in the adipose tissue of turkey (CHIN et al., 1992), liver of rats (POLLARD et al., 1980) and horse serum (PARK and PARIZA, 2000). However, the extent of synthesis and level of CLA is lower than in the ruminants. According to animal data, an intake of 3.0 g/d of CLA would be required for beneficial effects in humans (IP et al., 1994). The daily estimated consumption of CLA is under 1 g/d in the United States and in Germany (IP et al., 1991; ). Therefore, CLA enrichment of human diet could contribute to diet-based health prevention. In order to increase the content of CLA in ruminant products, nutritional modification of hydrogenation process in the rumen may be used (SCHMIDT et al., 1995; DHIMAN et al., 2000). The enrichment of products from monogastric animals with CLA, however, can be achieved by the addition of synthetic CLA sources to the diet. Several authors indicated that feeding diets containing CLA to laying hens resulted in effective deposition of CLA in egg yolk lipids (JONES et al., 2000; RAES et al., 2002; ). In many experiments dietary CLA induced significant alterations in lipid content and fatty acid composition of egg yolk and other tissues of laying hens and broilers (RAES et al., 2002; BADINGA et al., 2003). How-