Response of Production Performance, Nutrient Digestibility and Blood Metabolic Indices to Different ration of Palmitic to Stearic Acid in Holstein Cows' Diet

The experiment was conducted to investigate the effect of different ratio of palmitic acid to stearic acid in dairy cows diet. Total of 8 dairy cows (parity of 3.2 ± 0.6, milk yield of 40±3 kg/d and DIM of 56± 13) were randomly used in a 4×4 Latin square design over a 21-day experimental period. The experimental diets include different ratio of fat supplements were: 1-control diet 100P (100% palmitic acid), 2- 33S67P diet (33% stearic and 67% palmitic acid), 3-67S33P diet (67% stearic and 33% palmitic acid) and 4-100S diet (100% stearic acid). Individual dry matter intake and 3x milk production recorded at the last week of each period. Nutrients digestibility measured during 3 days of last week of experiment by collecting fecal from rectum before morning milking. The blood samples at d 19 taken from tail vein were used for metabolites and hormones analyze. The results showed that dry matter intake, digestibility of DM, fat, protein, NDF, milk and ECM yield, milk protein and lactose yield and percentage were not affected by different ratio of palmitic acid to stearic acid.  Replacing palmitic acid with stearic acid caused   decrease in FCM, fat percentage and fat/protein ratio (p<0.05). The concentration of plasma NEFA tended to be higher in cows fed 33S67P compared to 67S33P and 100S diets (p=0.07). In conclusion, present results showed that increasing diet stearic acid level led to decrease in milk fat and lactose percentage, without effects on milk yield efficiency.