The present tudy was conducted to determine the effects of different fat supplement on performance, milk composition and blood metabolites of Holstein dairy cows. To meet this objective, 112 Holstein dairy cows (88.2 ± 36.5 days in milk and producing 45.8 ± 6.9 kg of milk/d) were used in a change-over design with 21-d periods. Cows were grouped based on milk yield and days in milk (DIM). Each experimental period consisted of a 18-d diet adaptation period and a 3-d collection period. At the end of the first period, the diet of each group switched to another diet. Therefore, cows received 1 of the 2 following experimental diets in each period: (1) saturated free fatty acids (SFFAs), (2) n-capsulated fat (Table 1). All cows were fed twice daily (08:00 and 16:00 h). The TMR amounts offered and refused were measured daily for each group and the average of dry matter intake (DMI) determined daily for each group. Cows were milked 4 times daily at 0600, 1200, 1800 and 2400 h in a herringbone milking parlor. Milk yield for all cows was recorded and sampled at 0600 milking during the 3-d collection period for milk composition analysis. Milk fat, lactose and protein yield (kg/d) were calculated for the 3-d collection period, based on the product of the milk production yield and milk composition at 0600 milking on those days. Results indicate that DMI and milk yield were similar between treatments. Cows received n-capsulated fat supplement had lower 4 % FCM (28.1 vs. 31.2 kg DM/d), ECM (32.2 vs. 34.6 kg/d), fat yield (0.75 vs. 0.96 kg/d), fat percentage (1.75 vs. 2.29 %), FCM/DMI (1.22 vs. 1.32), and ECM/DMI (1.38 vs. 1.46) than cows fed with SFFAs. However, n-capsulated fat supplementation increased milk yield/DMI in comparison with SFFAs. The serum concentration of glucose, BHBA, NEFA, cholesterol, HDL, tri-glyceride, albumin, globulin, and total protein, BUN, AST and ALT were not affected by fat supplement source. The findings from this study suggest that feeding n-capsulate
