Text Box: Text Box: CHEMISTRY & NUTRITION Text Box: Effects of feed diet on milk composition and cheddar cheese properties Text Box: Francisco Parada-Rabell and Dr. ALvarez Text Box: Feeding ruminants with unsaturated fat alter the fatty acid profile of milk differently. Data are limited on fatty acid composition in milk when combinations of soybean and fish oils are added to feed. Additionally, there is some evidence that increasing dietary concentration of vitamin E may affect milk fatty acid composition, especially unsaturated fat. Hence, the characteristics of manufactured cheddar cheeses might be altered. Even though sorbitol is being used in commercial feed, little data exists on its effect on milk composition. The objectives of this study were to evaluate both the effects of dietary supplementation of unsaturated oils, vitamin E, and sorbitol on fatty acid concentrations in milk and the subsequent property changes of cheddar cheese. Four lactating Holstein cows were used in a Latin square design for 3 weeks, with milk collection occurring during wk 3 for composition analyses and production of cheddar cheese. Cows were fed 4 diets: 1) control diet (CNTL; 500 IU vitamin E), 2) 2% fish oil, 0.5% soybean oil, and 500 IU of vitamin E (FSO), 3) 2% fish oil, 0.5% soybean oil, and 2000 IU of vitamin E (FSOE), and 4) 1% sorbitol (SORB, dry form; 500 IU vitamin E). Oil supplemented diets resulted in lower proportions of palmitic, stearic, linoleic, and saturated fatty acids and higher proportions of unsaturated fatty acids in milk. The FSOE diet resulted in the highest proportion of unsaturated fatty acids in milk. Cheese yield was lower for the diets containing oil (7.8% versus 9.6%). Moisture and solids concentrations were similar among the cheeses. Crude protein concentrations (40.8, 49.2, 50.2, and 43.1% dwb, respectively) were lower in cheeses from cows fed the control diet. Fat concentration was also lower in cheeses from cows fed the FSOE diet (44.1, 31.2, 29.2, and 44.0% dwb, respectively). Cheeses from cows fed the FSOE & FSO diets were harder than those from CNTL and SORB diets (13.40 and 15.72 versus 5.81 and 6.65kgf, respectively). Results suggest that milk from cows fed fish-oil diets will likely have less fat content, and thus cheese characteristics, such as yield, texture, and protein-fat ratio will be altered.