Effects Of Different Doses Of Rumen-protected Glucose On Gastrointestinal Function And Body Metabolism Of Early Lactation Dairy Cows

Negative energy balance(NEB)is the common pathological basis of postpartum energy metabolic disorders including ketosis and fatty liver in dairy cows,which are mainly found in high-yield cows with day in milk more than 30 kg.Dairy cows in early lactation are prone to NEB,and the resulting body fat mobilization leads to the increase of plasma non-esterified fatty acid(NEFA)concentration,which affects milk fat,and thus restricts the development of dairy industry.Rumen-protected glucose(RPG)is a good glucose supplement,however,the application of RPG in early lactation of dairy cows has not been reported.Therefore,the purpose of this study was to explore the effects of RPG on the performance,gastrointestinal microbial composition and metabolism of early lactation cows,and to provide reference for effectively improving the energy balance and metabolic status of perinatal cows.Experiment 1: The purpose of this study was to evaluate the rumen stability of RPG and the effects of different doses on the rumen degradation characteristics of oat hay by using the nylon-bag technique.Chinese Holstein cows with permanent ruminal cannulas were selected to evaluate the stability of RPG in the rumen and the effects of different doses of RPG on the degradation characteristics of oat hay retained in the rume.The experiment was prefed for 7 d and tested for 3 d.The results showed that the rumen passage rate of RPG was 54.03 %,and the addition of 200 g/d RPG to the diet can alleviate NEB and regulated rumen fermentation while ensuring that the rumen degradation characteristics of oat hay are not significantly affected.Experiment 2: This study mainly revealed the mechanism of different doses of RPG to alleviate NEB of the early lactating dairy cows through serum untargeted metabolomics.Thirty-two multiparous Holstein cows in early lactation,blocked by parity,liveweight,and milk yield,were allocated to one of four treatments in a randomized block design.Treatments were: control(CON),low RPG(LRPG),medium RPG(MRPG)and high RPG(HRPG)with 0,200,350 and 500 g RPG per cow per day,respectively.The results showed that compared with other groups,the MRPG group changed the rumen environment,decreased serum concentrations of related indexes of NEB,and could increase glucose(GLU)concentration in serum.Dietary RPG supplementation affected ruminal p H and some volatile fatty acid(VFA)concentrations.The results of serum metabolomics showed that the metabolites with the largest contribution after RPG supplementation were mainly involved in lipid metabolism.The results of this study indicated that adding 350 g RPG to a cow’s diet in early lactation could improve energy balance by reducing fat mobilization.Experiment 3: This study used a combination of rumen microbes 16 S and metabolomics to elucidate the changes of rumen microbial composition and rumen metabolites of different doses of RPG’s rumen degradation part in early lactation dairy cows.Twenty-four multiparous Holstein cows in early lactation were randomly allocated to the same four groups and fed.MRPG supplementation increased bacterial richness and diversity and significantly increased the concentrations of short chain fatty acids in the rumen.RPG supplementation of different doses can change the diversity of microorganisms in the rumen and affect the rumen fermentation pattern and microbial metabolism,and a daily supplement of350 g RPG might be the ideal dose.Experiment 4: The objectives of the current study were to evaluate the impact of different doses of RPG supply on fecal microbiota and metabolome in early lactation dairy cows,and their correlation with each other.After the same treatment as above Experiment 3,the sample analysis found that MRPG increased the relative abundance of cellulolytic bacteria.Faeces metabolomics analysis showed that RPG supplementation could significantly regulate the carbohydrate metabolism and amino acid metabolism pathway,relieve lipolysis in dairy cows.Correlation analysis showed that some major differential bacteria were the crucial contributors to differential metabolites.Our analysis found that RPG supplementation can affect the fecal microbial components and metabolism,and 350 g RPG daily supplement might be the ideal dose.In conclusion,supplementation of 350 g RPG can effectively alleviate NEB,improve performance and rumen fermentation in early lactation,and is beneficial to the development of gastrointestinal microflora of dairy cows.