Effect Of Energy And Protein Level On Energy Metabolism And Productivity Of Dairy Cows

Three Chinese Holstein dairy cows were offered five kinds of ration consisted of high quality alfalfa hay, sheep grass hay and concentrate to study the effect of energy and protein level on energy metabolism, milk component and blood PUN, NEFA. The energy requirements of Chinese Holstein dairy cows were estimated based on the exam data. There were five kinds of concentrates: low energy and medium protein(Team C), medium energy and medium protein(Team A), high energy and medium protein(Team B), medium energy and low protein(Team E) and medium energy and high protein(Team D) .The ratios of concentrate to forage from Team A to E were 58: 42, 64: 36, 56: 44, 54: 46 and 57: 43.When the protein level was stable and the energy level improved, Team C, A, B were compared: FE had no significant differences (p>0.05), but there was a down-trend betweenTeams for 1.12MJ/day and 4.50MJ/day; UE had no significant differences (p>0.05); Methan energy loses and total HP were significant greater (p<0.05); The digestibility and metabolisbility of GE had no significant differences (p>0.05); There was a significant difference of metabolisbility of DE about Team C and A comparing with Team B (p<0.05); Milk energy was relatively stable (p>0.05); There was a significant difference of retained energy and retained energy for weight about Team C and A comparing with Team B (p<0.05); Blood PUN and NEFA had little variation (p>0.05); Milk yield and milk lactose were relatively stable (p>0.05); There was a declined trend of milk fat ratio and an up-trend of milk protein ratio, but there were no significant differences between Teams (p>0.05).When the energy level was stable ane the protein level improved, Team E, A, D were compared: FE was relatively stable (p>0.05); UE improved progressively (p<0.05); Methan energy output declined progressively (p<0.05) and total HP had an up-trend but no significant differences between Teams ((p<0.05); The digestibility of GE were relatively stable (p>0.05); There was a significant difference of metabolisbility of GE about Team E comparing with Team A and D (p<0.05); Milk net energy and retained energy changed little (p>0.05) and retained energy of weight had a significant difference between Team E, A and D (p<0.05); Blood PUN declined significantly (p<0.05) and blood NEFA changed little (p>0.05); Milk yield and milk lactose ratio were stable (p>0.05); Milk fat ratio and milk protein ratio had an up-trend (p>0.05).We could estimate milk energy requirement according to milk component and milk yield, and the result was 3.27±0.016MJ/kg. With the regression analysis, the maintaining net energy requirement was 0.078Mcal/kgBW^0.75.