INCLUSION OF OXIDIZED FISH-OIL IN MINK DIETS .1. THE INFLUENCE ON NUTRIENT DIGESTIBILITY AND FATTY-ACID ACCUMULATION IN TISSUES

In a feeding experiment with 18 male, adult, pastel mink over a period of 15 weeks, the influence of high amounts (55 % of metabolizable energy) of fresh and oxidized fish oil (200 and 400 meg. O-2/kg oil) on performance and fatty-acid accumulation in liver and inguinal fat was examined. The apparent digestibily of macronutrients, fatty acids and alpha-tocopherol was determined during the eighth week of the experiment. The quality of the experimental oils was followed during oxidation and storage (13 weeks, -80 degrees C exclusion of light and oxygen). During storage, the peroxide values of the respective oils were kept relatively stable but a considerable loss of n-3 fatty acids was recorded especially in the heavily oxidized oil (400 meq. O-2/kg oil). The apparent digestibility of crude fat decreased from 95 % (fresh oil) to 91 % (200 meg. O-2/kg oil) and 74 % (400 meg. O-2/kg oil). The apparent digestibility of total fatty acids decreased in parallel. The apparent digestibility of alpha-tocopherol was in the range of 60 % and was not influenced by the dietary fat quality. Feed intake, growth and performance in the mink were negatively affected, in particular by the heavily rancid fish oil. The fatty acid composition of the liver and inguinal fat clearly reflected the marine origin of the dietary fat source. The accumulation of long-chain fatty acids (C20, C22) was extremely high in both liver (28-31 % of total fatty acids) and inguinal fat (38-42 %).