| The present study consists three experiments in vivo and vitro to study the approprioate supplementary level of nicotinamide (NAM) in the diet of lactating dairy cows. The first experiment was conducted to study the effect of different NAM supplement levels on fermentation in vitro of lactating dairy cows; The second and the third experiments were conducted to study the effect of different NAM supplementary levels in vivo of early and middle lactating dairy cows through the biochemical parameters of blood, milk yield, milk composition and the concentration of NAD and NADP to definite the approprioate supplementary level of NAM.Experiment One: Effect of different nicotinamide supplementary levels on fermentation in vitro of rumen microorganism.Three lactating Holstein cows fitted with permanent rumen cannula were used to provide rumen fluid in vitro. Basal diet was used as fermentation substrate. The trial was designed of five treatments with three replicates. Treatments were control which was the basal diet as fermentation substrate and other treatments were basal diet supplemented with 0.3, 0.6, 0.9 and 1.2 mg NAM /g DM, respectively. The result of the experiment showed: pH was not changed significantly at 4 h (P>0.05), control pH at 8 and 12 h was lower than 0.6 mg NAM /g DM, and 1.2 mg NAM /g DM was lower than all other NAM treatments (P<0.05); Concentration of VFA and the degradability of DM, CP and NDF were not significantly different (P>0.05) among all treatments. Protozoan Crude Protein (PCP) concentration was greater (P<0.05) for 0.3 vs 0.9 and 1.2 mg NAM /g DM, and 1.2 was lower than 0.3 and 0.6 mg NAM /g DM, and the concentrations of Bacterium Crude Protein (BCP) among treatments were in no differences (P>0.05). It was concluded that adding nicotinamide was no effect on the degradability of substrate, and adding approprioate supplementary level of nicotinamide can help for the growth of rumen protozoa, but higher additions possibly had no effect. Experiment Two: The study on approprioate supplementary level of nicotinamide in the diet of early lactating cowsForty Holstein cows in early lactating dairy cows were selected into four treatments with ten replicates randomly. Treatments were control which was fed the basal diet and other treatments were basal diet supplemented with 6, 12 and 18 g/d NAM, respectively. The result of the experiment showed: As the supplementary of NAM added, the concentration of NAM was linealy and significantly increased both in plasma and milk (P<0.05); Milk yield, milk fat content, lactose content, total solid content and milk protein yield was not change significantly (P>0.05), but in 60 d, the milk protein content of the group of adding 18g/d NAM was significantly increased than that of control and adding 12 g/d NAM (P<0.05), and the fat yield of the group of adding 6 and 12 g/d NAM was significantly increased than that of control and adding 18 g/d NAM (P<0.05); The concentration of NEFA, TC, HDL, LDL, VLDL, Glu of plasma was not significantly changed (P>0.05), but in 60 d, the concentration of BHBA of the group of adding 6g/d NAM was significantly decreased than that of control (P<0.05), and the concentration of TAA was significantly increased than that of control (P<0.05); In 60 d, as the supplementary of NAM added, the concentration of NAD of the whole blood was increased, and the group of control of the rate of NAD:NADP<1, and the supplementary groups of the rate of NAD:NADP>1; The group of adding 12 and 18 g/d NAM of the value of the rate of NAD:NADP was significantly increased than that of control(P<0.05). It was concluded that: in this feeding condition (the niacin equivalence was 72.09mg/kg), as the supplementary of NAM added, the concentration of NAM was linealy and significantly increased both in plasma and milk; the concentration of NAD in the whole biood was conducetd to evaluate the effectiveness of dietary nicotinamide; fat yield was increased, concentration of BHBA was decreased and the concentration of TAA was increased in approprioate supplementary level of nicotinamide in the diet. The approprioate supplementary level of nicotinamide in the diet of early lactating cows was 6g/d.Experiment Three: The study on approprioate supplementary level of nicotinamide in the diet of middle lactating cowsForty Holstein cows in middle lactating dairy cows were selected into four treatments with ten replicates randomly. Treatments were control which was fed the basal diet and other treatments were basal diet supplementaryed with 6, 12 and 18 g/d NAM, respectively. The result of the experiment showed: As the supplementary of NAM added, the concentration of NAM was linealy and significantly increased both in plasma and milk (P<0.05); Milk yield, milk protein content, lactose content, milk protein yield was not change significantly (P>0.05), but in 30 d,. fat content of supplementary groups were increased than that of control, the milk fat yield of the group of the group of adding 12 and 18 were increased than control, and in 60 d, the fat production of the group of adding 6 and 12 g/d NAM was significantly increased than that of control (P<0.05); The concentration of NEFA, TC, HDL, LDL, Glu, Urea of plasma was not significantly changed (P>0.05), but in 60 d, the concentration of TAA was significantly increased than that of control (P<0.05); In 60 d, as the supplementary of NAM added, the concentration of NAD of the whole blood was increased, and the group of control and the supplementary group of the rate of NAD:NADP>1; The group of adding 12 and 18 g/d NAM of the value of the rate of NAD:NADP was significantly increased than that of control(P<0.05). It was concluded that: in this feeding condition (the niacin equivalence was 72.09 mg/kg), as the supplementary of NAM added, the concentration of NAM was linealy and significantly increased both in plasma and milk; the concentration of NAD in the whole biood was conducetd to evaluate the effectiveness of dietary nicotinamide; fat yield was increased, concentration of BHBA was decreased and the concentration of TAA was increased in approprioate supplementary level of nicotinamide in the diet. The approprioate supplementary level of nicotinamide in the diet of middle lactating cows was 6g/d.. |
