| Organic milk production follows the concept of health and quality,and protein is the key foundation to ensure that cows provide high-quality milk.The utilization and conversion efficiency of protein in dairy cows is limited.Excessive use of protein levels will not only cause waste but also produce negative effects on the liver.Therefore,providing the appropriate dietary protein level can not only improve efficiency and save costs,avoid environmental pollution,but also more in line with the concept of organic farming.In this study,the value of organic feed and rumen degradation rats were firstly evaluated,and then the effects of decreasing dietary crude protein(CP)level in organic production on nitrogen utilization,production performance,serum indexes,rumen fermentation,microflora and metabolism of dairy cows were investigated.The mechanism of adjust provides a basis for reducing ration cost of production in organic production.During the experiment,a group of conventional diet was added as a reference to study the effects of conventional diets and organic diets on dairy cows under the same CP level.Experiment Ⅰ: Determination of Nutritional Value and Rumen Degradation of Organic Feed.Fourteen organic feeds(Including two types of silage,four types of roughage,eight types of concentrate)were tested for the content of nutrient and amino acid,which were used in organic farming.Our results revealed that: three roughages(alfalfa hay(AF),oat hay(OH)and whole corn silage(CS))and three concentrates(soybean cake(SC)、 wheat bran(WB)and corn grain(CG))was selected to investigate rumen degradation characteristics(nylon bag method)of organic feeds’ dry matter and crude protein content.Our analysis revealed that: among SC、WB and CG,the effective degradation rate(ED)of dry matter(DM)is SC(87.89%)> WB(73.32%)> CG(64.25%);the ED value of CP is CG(82.37%)>WB(82.40%)> SC(60.47%).Among CS,OT,and AF,the effective degradation rate(ED)of DM is CS(72.68%)> OT(59.97%)> AF(58.89%);the ED value of CP is AF(76.46%)>CS(72.03%)>OT(71.99%).The determination of conventional nutrients and degradation rats of organic feed provides data support and basis for the later experiments.Experiment Ⅱ: Effects of different dietary protein levels on nitrogen utilization,production performance and blood indexes of dairy cows.In this experiment,forty Holstein dairy cows were divided into four groups.Cow were fed with four diets with different CP levels(17%(normal);17%(organic);16%(organic);15%(organic)on DM basis;groups were named by CP17 N,CP17,CP16,CP15).The experiment was carried out for 75 days,the first 15 days were the pre-feeding period.Our results revealed that: reducing the dietary CP level to 16% can improve the apparent digestibility and feeding efficiency of dairy cows,the apparent digestibility of DM,CP,neutral detergent fiber(NDF)in CP16 group were higher(P < 0.05)than other three groups,and the feed efficiency of CP17 group was lower(P < 0.05)than other three groups.Both nitrogen utilization and production performance were affected by reducing dietary CP levels,the content of milk urea nitrogen and blood urea nitrogen in CP17 N group and CP17 group were higher than other two groups.There was no significant(P > 0.05)difference in milk yield among the four groups.But the yield of 4%FCM in CP17 group were highest,the milk content of total amino acid in CP17 group were significantly higher(P < 0.05)than CP16 group and CP15 group.There was a large difference in milk fatty acid content between the organic groups and the normal group,the content of MUFA in CP17 N group was lower than three organic groups,especially CP17 group.The above data suggest that reducing dietary protein levels to 16% will improve the feeding efficiency and nutrient digestibility of dairy cows,but will have an impact on nitrogen utilization and production performance.Experiment Ⅲ: Effects of different dietary protein levels on rumen fermentation,microflora and metabolome of dairy cowsThe experimental design was the same as that of Experiment 2.The results show that:the rumen content of ammonia nitrogen,microprotein,acetate,propionate and total volatile acids in CP17 group was no significant(P > 0.05)difference with CP16 group.The content of total volatile acids in CP15 group was lower(P < 0.05)than three organic groups.The abundance of Prevotella in CP17 N group was higher(P < 0.05)than CP17 group.Akkermansia,Dunaliella,Helicobacter and Alternaria were not detected in the CP17 N group.The results of rumen metabolomics analysis showed that 1031 metabolites were identified in the four groups in positive ion mode,among which the metabolites between the CP17 N group and the CP15 group had the largest difference,with 231 species,of which 143 were upregulated and 88 were down-regulated.There were 92 metabolites with the smallest difference between the CP17 group and the CP16 group,of which 61 were up-regulated and31 were down-regulated.After enriching the KEGG function of the microbial flora,it was found that with the decrease of the dietary CP level,the functions of amino acid metabolism,energy metabolism,enzymes and coenzyme factors were gradually strengthened.Pairwise comparison of KEGG pathway enrichment in metabolome was not significant(P > 0.05).The above data show that reducing dietary protein levels to 16% will not have a significant impact on the rumen fermentation of dairy cows,which may be due to the change in the proportion of some bacteria genera to change the microbial metabolism.In conclusion,firstly this study clarified the nutritional value and degradation of organic feed,and secondly,this study found that reducing the dietary CP level to 16% will improve the feeding efficiency and nutrient digestibility of dairy cows,but it will still affect the nitrogen utilization and production performance.Finally,this study found that reducing the dietary CP level to 16% would not affect the rumen TVFA content,rumen fermentation pattern and rumen-dominant phyla.At the same time,this study found that the unsaturated fatty acid content of milk was significantly different between the organic group and the conventional group,and some species of bacteria(Akkermansia)unique to the organic dairy cows. |
