| The purpose of this study was to evaluate the effects of malic acid(MA)on the production performance,rumen fermentation and rumen microbial diversity of dairy cows.This study contained two parts:in vitro and in vivo study.Experiment 1:Batch culture technique was used to evaluate the effect of malic acid on rumen fermentation performance.In the experiment,rumen fermentation was simulated by in vitro method.Three Chinese Holstein steer with permanent rumen fistula were selected as rumen fluid donors.Four groups(group Ⅰ,group Ⅱ,group Ⅲ and group Ⅳ)were added with 0,5,10 and 15 mmol/L malic acid respectively.Group Ⅰ was considered as the control group.Each group was cultured in vitro for 8,16,24 and 48h with 3 replications.The results showed that:1)compared with the control group,the gas production of group Ⅱ,group Ⅲ and group Ⅳ increased with the increase of malic acid addition,and group Ⅳ reached the maximum value with significant difference(P<0.05);Dry matter disappearance(DMD)in group Ⅱ,group Ⅲ and group Ⅳ was significantly higher than that in the control group(P<0.05),and there was no significant difference among the three groups(P>0.05).2)With the increase of malic acid addition,the pH of the culture solution in each group showed a downward trend.The pH in groupⅣ was significantly lower than that in other groups(P<0.05),and the pH range was 6.24-6.60;After 8,16 and 48 h of fermentation,NH3-N concentration in group Ⅲ was significantly higher than that in control group and group Ⅱ(P<0.05),but there was no significant difference between group Ⅲ and group Ⅳ(P>0.05).After 16,24 and 48 h of fermentation,the concentration of microbial protein(MCP)in group Ⅲ was significantly higher than that in control group and group Ⅱ(P<0.05),but there was no significant difference between group Ⅲ and group Ⅳ(P>0.05).3)The concentrations of acetic acid,propionic acid and butyric acid in group Ⅲ were significantly higher than those in control group and group Ⅱ(P<0.05),but there was no significant difference between group Ⅲand group Ⅳ(P>0.05).The total volatile fatty acid(TVFA)concentrations in group Ⅱ,group Ⅲ and group Ⅳ were significantly higher than those in control group(P<0.05).After 8,16 and 24 h fermentation,compared with the control group,the ratio of acetate to propionate was lower in group Ⅲ and group Ⅳ(P<0.05),while no difference between the two groups(P>0.05).The results showed that adding 10 mmol/L malic acid could increase rumen gas production and dry matter disappearance rate,increase the concentration of acetic acid,propionic acid,butyric acid and TVFA in fermentation broth,reduce the ratio of ethylene to propylene,improve rumen fermentation and increase rumen microbial fermentation activity.Experiment 2:Effects of malic acid on performance,blood biochemistry,rumen fermentation parameters and microbial diversity of dairy cows in early lactation.In this experiment,60 Chinese Holstein cows with similar body condition in early lactation were selected,including lactation days(average lactation days DIM 62±10 d),parity(1-2 parity),daily average milk yield(35.5±4.6 kg/d),and early lactation(P>0.05).The experiment was designed by single factor and completely random,and was randomly divided into three groups(group C,group L and group H),with 20 replicates in each group and 1 cow in each replicate.The three 100groups added 0,50,100 g malic acid to the basal diet for 8 weeks.The results showed that:1)The total milk yield and 4%standard milk in group H were significantly higher than that in group C(P<0.05.2)compared with group C,the crude protein digestibility of group L and group H was significantly increased(P<0.05).Digestibility of neutral and acidic washing fibers in group H was significantly higher than that in groups C and L(P<0.05).The organic matter digestibility increased linearly in the three groups(P<0.05).Compared with group C,calcium digestibility in group H was significantly increased(P<0.05),while phosphorus digestibility was not significantly different among groups(P>0.05).3)compared with group C and group L,blood glucose in group H was significantly increased(P<0.05).The total protein of MA group was significantly higher than that of the control group,increased by 6.38%and 9.74%respectively(P<0.05).The albumin level of group H was significantly higher than that of control group and group L,and the albumin level increased linearly with the increase of MA addition.The level of alkaline phosphatase in group H was significantly higher than that in control group and group L(P<0.05).Compared with the control group,malondialdehyde content in group H was significantly reduced by 21.83%(P<0.05).4)the pH of rumen fluid in group H was significantly higher than that in control group and group L(P<0.05).The NH3-N level in group H was significantly lower than that in control group and L group(P<0.05).Compared with the control group,the acetic acid content in group L and group H was significantly increased(P<0.05).Propionic acid content in group H was significantly higher than that in control group and group L(P<0.05).The total volatile fatty acid content in group L and group H was significantly higher than that in the control group,increasing by 14.62%and 23.55%respectively(P<0.05).The ratio of ethylene to propylene in the three experimental groups decreased significantly with the increase of MA addition(P<0.05).5)high-throughput sequencing results showed that there was no significant change in chaol index and shannon index among the three treatment groups(P>0.05).Through multiple analysis and comparison of rumen microflora and microflora abundance,it can be concluded that the effect of malic acid on rumen microflora level in diets shows that the dominant microflora in the three groups are chlamydomonas,bacteroides and Proteobacteria.Compared with the control group,the abundance of chlamydomonas in group L and group H is significantly increased(P<0.05),From the subordinate level,there is no significant difference among the three treatment groups of Prevost’s genus,which is the main dominant genus(P>0.05),but the relative abundance of Vibrio butyricum in group H is significantly higher than that in groups C and L(P<0.05).According to the thermogram analysis of the relationship between species and phenotypes of microorganisms at the genus level,it can be seen that the genera Microbacter,Amino Acid Coccus,Sharptomyces and Bulleidia play a vital role in rumen volatile fatty acid synthesis,ammonia nitrogen utilization and maintenance of rumen acid-base balance.In conclusion,under the existing experimental conditions,the addition of 100 g/d malic acid to the diet of dairy cows in early lactation can improve the production performance of dairy cows,improve rumen fermentation types,promote the utilization of energy and nitrogen,and maintain rumen microecological stability. |
