Influence of dietary fat, L-carnitine and niacin on milk yield and milk composition of dairy cows in midlactation

Two studies were conducted to evaluate the effect of dietary fat, L-carnitine, and niacin on milk production and milk composition in midlactation dairy cows. Eight multiparous lactating dairy cows were used. The studies were carried out with 2x2 factorial arrangements in a 4x4 Latin square design. The treatments in the fat and L-carnitine study (FLC) were: 1) no fat (NF) and no L-carnitine, 2) no fat and 0.045 % L-carnitine, 3) 3.6 % fat (as fed) and no L-carnitine, and 4) 3.6 % fat and 0.045 % carnipass. In the L-carnitine and niacin study (LCN), rations containing dietary fat (3.6 %) were used for all treatments and treatments were: 1) no L-carnitine and no niacin, 2) no Lcarnitine and 0.045 % niacin, 3) 0.045 % carnipass and no niacin, and 4) 0.045% carnipass and 0.045% niacin. In the FLC study, dietary fat increased milk yield (P <0.05) and tended to increase milk NPN content (P =0.10) and improved milk production efficiency (milk yield/dry matter intake, P < 0.01). In contrast, milk fat, milk protein, true protein and casein nitrogen (P < 0.05) were reduced by dietary fat. L-carnitine resulted in decrease in milk yield and casein yield (P < 0.05) in the FLC. In connection with milk yield; protein yield had a tendency to decrease (P =0.08) by L-carnitine. Only non-fat solids are affected (P < 0.01) by the interaction between the dietary fat and L-carnitine. Milk yield and milk production efficiency also tended to be lower (P = 0.12 and P = 0.07) with L-carnitine in the LCN study. Niacin had no effect on milk yield and composition, except for the proportion of casein N to total N. The proportion of casein N to total N had a tendency to be higher (P =12) with L-carnitine and niacin separately. It could be concluded that dietary fat may increase milk yield and decrease milk fat, milk protein and L-carnitine supplementation may decrease milk yield, niacin supplementation did not affect with yield, composition and other parameters of diary cows in mid lactation fed a diet containing 60 % concentrate and 40% of alfalfa ha