Two forms of nonenzymatically browned sunflower seeds were evaluated in two lactating dairy cow trials to determine their effect on animal performance and ruminal fermentation. In the first experiment, eight lactating Holstein cows were used in a replicated 4 x 4 Latin square with 3-wk periods. Four treatments were used: (1) control diet with no added lipid, (2) sunflower oil (SFO), (3) untreated, ground sunflower seeds (GSF), and (4) nonenzymatically browned, ground sunflower seed (NEBS). In the second trial, thirty cows were assigned to one of three diets for a period of 6 wk. Diets were fed as total mixed rations that contained 40% of a 1:1 mixture of alfalfa and corn silage and (1) wet corn milling product (CMP) with no added lipid, (2) CMP + nonenzymatically browned sunflowers (NEBS), and (3) CMP + tallow. Our objective was to investigate the effect of supplementing a diet containing high amounts of wet corn milling product with RUP and RUL from nonenzymatically browned sunflowers on efficiency of fat-corrected milk production and composition of milk fatty acids. The results of these studies indicate that the oil in NEBS was partially protected from ruminal biohydrogenation and successfully elevated the desirable poly- and monounsaturated fatty acid content of milk fat, reduced saturated fatty acids, and increased CLA content in milk fat. The experiments also demonstrated that NEBS accomplish the positive alterations in milk fatty acid composition without reducing the output of milk fat. (Abstract shortened by UMI.