Study On Efficiency Of Converting Dietary Nitrogen Into Milk Nitrogen And Its Affection Factors In Holstein Lactating Dairy Cows

This paper mainly studied on efficiency of converting dietary nitrogen into milk nitrogen and its affection factors in Holstein lactating dairy cows in Shandong provience,The aim was improving nitrogen utilization of Holstein lactating dairy cows in our provience.The study was including 3 expriences. In Exp.1, the efficiency of converting dietary nitrogen into milk nitrogen of total 18 Herds in seven farms of Shandong Province was investigated, and its affection factors was also determinated. The results showed that milk production of the 18 herds was from 6.02kg to 28.37kg; the nitrogen utilization on CP was from 12.26% to 27.99% and the nitrogen utilization on TP was from 10.77 to 30.98%. After the Primary Component Analysis and the multiple linear regression,the fellow formula was gotten : Nitrogenutilization=36.955-1.446*CP(%DM)-0.833*DMI(kg/d)+1.108*milk production(kg/d)(R2=0.87). The affection factors of efficiency of converting dietary nitrogen into milk nitrogen in Holstein lactating dairy cows in Shandong provience was CP,DMI and milk production.In 4×4 Latin square design of Exp.2, four Holstein dairy cows with the same ages, body weight , parity and lactation period were used to study on the effection of protein level in diet on efficiency of converting dietary nitrogen into milk nitrogen. The treatments were four levels of MP:91g/KgDM,99g/kgDM,106g/kgDM,113g/kgDM(groupA, groupB, groupC and groupD). The results showed that efficiency of converting dietary nitrogen into milk nitrogen in groupA, groupB, groupC and groupD were 25.28%,23.55%,21.54% and 20.01% respectively;GroupA and groupB was higher than groupD significantly(P<0.01) . When the levels of MP in diet was increased, the nitrogen utilization was decreased.Exp 3 was condueted to study the effcts of.rumen Protected Methionine and lysine on dairy cows nitrogen utilization.Six lactating 90 to 110 day Holstein dairy cows with the same ages, body weight and parity were devided into two groups with different levels of MP(81g/kgDM, 96g/kgDM),each group had 3 cows. Each group 4×4 Latin square design was used,.The treatments were adding three levels of rumen Protected Methionine and lysine in diet( 15g,32g and 0g respectively). The results showed that nitrogen utilization and economic benefits were better in treatment of adding 32g rumen Protected Methionine and lysine in diet than the other treatments.