| Improving the efficiency of dietary nitrogen conversion in dairy cows is a key issue in cu rrent dairy nutrition research.Dairy cows have higher feed conversion efficiency than other ru min ants but lower nitrogen utilization efficiency,which not only increases the feeding cost,bu t also leads to the increasing environmental problems related to nitrogen pollution.Rumen am monia nitrogen and blood urea nitrogen concentrations are both important indicators that can b e used to evaluate nitrogen balance and protein utilization efficiency of dairy cows.In this pap er,meta-analysis was used to study the main dietary nutrients that affect rumen ammonia nitro gen and blood urea nitrogen concentrations.The datum was collected from 230 English literat ure published between 2010 and 2022,involving a total of 830 trials.Single factor regression,stepwise multiple regression and local regression were used to establish the mathematical mod els of the correlation variables that could be routinely measured and had significant influence on rumen ammonia nitrogen and blood urea nitrogen,and their correlations were analyzed.In this study,the content of nutrients in different diets(percentage of dry matter)was as f ollows:Crude protein(CP),Neutral detergent fiber(NDF),Starch(Starch),Rumen degradabl e protein/Rumen non-degradable protein(RDP/RUP),metabolic protein(MP),milk productio n(MY),milk protein content(MProt%),milk protein production(MPY),milk urea nitrogen c oncentration(MUN)and dry matter intake(DMI)was correlated with rumen ammonia nitroge n concentration(RAN)and blood urea nitrogen concentration(BUN).The results of single factor regression model showed that MY(R2=0.134),CP%(R2=0.113)and MUN(R2=0.526)were the single factor that produced significant regression on rum en ammonia nitrogen concentration.According to the regression model,RAN was significantl y positively correlated with MY,MUN,CP%,NDF%and MProt%(P<0.05 or P<0.01),and negatively correlated with Starch%,DMI and MPY(P<0.01).There was no significant corre lation with MP and RDP/RUP(P>0.01).BUN had significant or extremely significant positi ve correlation with MUN,CP%,DMI,MP,MProt%and MPY(P<0.05 or P<0.01),but had no significant correlation with NDF%,Starch%,RDP/RUP and MY(P>0.01).By stepwise multiple regression principal component analysis,it was found that 4 predict ors were significant in rumen ammonia nitrogen mixed regression model,and 3 predictors wer e significant in blood urea nitrogen mixed regression model.The reliability and stability of the model were evaluated by analyzing the root mean square error(RMSE),Akaike information t heory criterion(AIC)value and consistency correlation coefficient(CCC),and the mean squar e prediction error was decomposed into mean deviation(MB)and slope deviation(SB).The d atum was divided into two groups,2/3 for model building and 1/3 for testing.The deviation be tween the predicted value of the model and the actual observed value was analyzed to test the practicability of the model.Finally,the multivariate linear model with the best fitting effect w as obtained:RAN=-10.222-0.287MY+1.136CP%+0.262NDF%+0.332MUN(R2=0.0.315,R MSE=1.35,CCC=0.89,AIC=1008);BUN=-8.633+0.781MUN+0.249DMI+2.193MProt%(R2=0.511,RMSE=1.5,CCC=0.87,AIC=261).The results of multiple regression equation showed that dietary crude protein content was closely correlated with rumen ammonia nitrogen and blood urea nitrogen concentration,and milk yield and milk protein content were significantly correlated with rumen ammonia nitroge n concentration.In order to improve the lactation performance of dairy cows during productio n,the multiple regression equation of rumen ammonia nitrogen and blood urea nitrogen can be used to adjust the protein and energy levels in the total diet according to the internal regulatio n mechanism of rumen ammonia nitrogen,so as to rationally supply nutrients,improve the eff iciency of dietary nitrogen conversion and reduce feed cost,providing theoretical reference fo r the establishment of precise nutrition model and the development of dietary formula. |
