The effect of different types of fat supplementation on the flow of fatty acids to the duodenum was estimated on three milking sheep fitted with duodenal re-entrant cannula in a 3 x 3 Latin square design consisting of three experimental diets differing in the percentage of supplemental fat. The basic ration for the control group consisted of meadow hay and concentrate (60:40) and was supplemented for experimental groups with soyabean oil, linseed oil, tallow, Bergafat^® preparation or fish oil at a level of 0 (control), 4 and 6% in dry matter. Duodenal digesta was analyzed for fatty acids content. All of fats used, of both vegetable and animal origin, caused statistically significant changes in the passage of fatty acids to the duodenum. Soyabean oil added to sheep rations significantly decreased levels of particular saturated fatty acids and also the sum of saturated fatty acids. In response to supplementation with linseed oil, a source of polyunsaturated fatty acids, the level of MUFA and PUFA in the duodenum increased (P<0.05). Under the fish oil treatment we observed a decrease (P<0.01) in the levels of two saturated fatty acids, lauric and palmitic. Also most of the detected unsaturated fatty acids were affected by fat treatment. Under Bergafat^® conditions, the passage of fatty acids to the duodenum did not point to any modifications in the fatty acids profile, except the concentration of oleic acid, which tended to increase (P<0.05). With the addition of tallow to sheep rations, the concentration of some fatty acids in duodenal digesta decreased significantly.