Nitrogen Utilization Efficiency Of Dairy Farms And Effect Of Crude Protein Level On Nitrogen Emission Of Dairy Cows

In order to reduce nitrogen emissions and increase the nitrogen utilization of dairyfarms, this paper studied two experiments.Exp.1Nitrogen utilization efficiency of dairy farms. Feed samples (including avariety of feed ingredients and total mixed ration)、milk samples and faces samples ofhigh-yielding dairy cows were collected from25representative dairy farms fromHenan province (Numbered1to25). All the intake and milk production wererecorded to study the nutritional status of various dairy diet, feed efficiency andnitrogen utilization, and analysis the correlations among indicators. The resultsshowed that:（1）Crude protein level of25dairy farms are between11%and18%, the range ofdry matter intake is16~27kg/d, the minimum average milk yield is25kg/d, and feedefficiency (milk feed ratio) in between0.80and1.59. Milk fat changed greatly in25dairy farms from2.07%to4.30%, milk protein, lactose, and total solids did notchanged dramatically, and normal range of milk urea nitrogen was10~16mg/dL.（2）The average of intake nitrogen reached556.96g/d; and the average milk N was131.29g/d in25dairy farms. The nitrogen utilization of over90%dairy farmsreached20%or more.（3）The result showed that between crude protein content and feed efficiency has nocorrelation, but and nitrogen utilization has negative correlation, while crude proteinand milk urea nitrogen content showed a positive correlation. Lys, Met and feedefficiency and nitrogen utilization is almost no correlation.Exp.2Effect of crude protein level on nitrogen emission of dairy cows. According toprinciple of the same parity, and similar calving time and milk yield,48high-yield and lean body condition of the Holstein cows were selected as test cows.12cowswere randomly divided into four groups (A, B, C, D), and fed with four different diets.Group A,control group,was fed with basal diet with the crude protein content17.07%,B, C, D groups were supplemented with4%,8%and12%protein, and crudeprotein contents were17.92%,18.55%,19.17%respectively. Trial period lasted60days, and the metabolic tests have been set at the last three days. In the trial period,milk yield, feed intake, the amount of left feeding of each dairy cows have beenrecorded. The results showed that:（1）Diets supplemented with different levels of crude protein has influential on drymatter intake of dairy cows. Group B and C DMI have been declined and group DDMI increased comparing with group A, but there were no significant difference (P>0.05). Different amounts of crude protein had no significant effect on milk productionand feed efficiency.（2）Different dietary crude protein content has no effect on milk composition andmilk urea nitrogen levels(P>0.05), and nitrogen content of each diet increased withthe increasing crude protein content, but it was within the normal range of10~16mg/dL. Lipoprotein ratio was within the range of1.12to1.36. However milkprotein content of D group was significantly higher than A group.（3）The effects of different dietary crude protein content on body condition score,body height, body length and daily gain of dairy cows were not remarkably (P>0.05).（4）Different dietary crude protein content had no effect on milk N, fecal N, Nretention, nitrogen utilization (milk N/feed nitrogen), milk N accounted for theproportion of N intake, urinary N accounted for the proportion of N intake, fecal Nrepresenting the proportion of N intake and milk N, urea N, fecal N accounted for theproportion of N digestion and N digestibility, but there was still a little fluctuation onthe nitrogen utilization. Compared with the Group A, the N intake, urea N, Ndigestion and excretion of nitrogen of Group B and C cows had no significantdifference (P>0.05), while N intake, urinary N and excretion of nitrogen of group Dshown significant difference (P <0.01).（5）Different dietary crude protein content had no effect on GPT, GOT, ALP, TP,ALB, GLU, TG, CH,BUN HDL, LDL and blood Ca and P (P>0.05), which meansdifferent dietary crude protein content had no significant effect on blood biochemicalindicators. However, TP and GLU levels increased with the increasing of proteincontent, while the content of BUN presented fluctuation, but there were no significant difference (P>0.05).