| Non-fiber carbohydrate(NFC)and Neutral Detergent Fiber(NDF)in diets are important components of ruminant nutrition.Although the applications of different dietary NFC/NDF ratios in dairy production have been reported,there are few in late-lactating cows.The dynamic changes and correlations of rumen fermentation parameters and bacterial microflora in vitro are rarely studied.In this experiment,the effects of different dietary NFC/NDF ratios on the performance,blood biochemical indexes and antioxidant indexes of dairy cows were tested.In addition,the dynamic changes of rumen fermentation parameters and bacterial microflora were studied with different dietary NFC/NDF ratios in vitro.This thesis includes two sections.Section one:Eighteen Chinese-Holstein cows using 3×3 Latin square design,were randomly divided into three groups(6 cows in each group)according to parities(2.00±0.22),days in milk(202.53±17.13 d),and milk production(24.47±1.27 kg/d).Cows in treatments were fed 3 types of total mixed rations with different NFC/NDF ratios(A,1.38;B,1.19;C,1.08).The experiment was conducted in 3 periods with 28 days each period.On day 14,21,and 28 of each period,feed intake and milk yield were recorded and milk samples(approximately 50 mL)were collected.On day 28 of each period,blood samples(approximately 10 mL)was collected via the tail vein.The results showed that the serum T-AOC(total antioxidant capacity)in group B was increased and MDA(malondialdehyde)was decreased compared to group A(P<0.05).For milk yield,milk composition and blood biochemical indexes,the three groups did not differ significantly(P>0.05).In summary,proper reduction of dietary NFC/NDF ratio has no significant effect on lactation performance and blood biochemical indexes in late-lactating cows.The reasonable dietary NFC/NDF ratio(1.19)can improve antioxidant capacity and maintain the health of dairy cows.Section two:Three types of total mixed rations with different NFC/NDF ratios(A,1.38;B,1.19;C,1.08)were used as substrates for fermentation in vitro.Gas production(GP)was measured at 2,4,6,12,18,24,36,and 48 h after initiation of incubation.After incubation for 6,12,24,and 48 h,samples were collected from fermenter liquids for analysis of the pH,lactate,NH3-N,MCP,VFA and bacterial 16S rRNA gene sequencing.The results showed that GP,pH,MCP,NH3-N,propionate,isovalerate and acetate/propionate were significantly affected by dietary NFC/NDF ratios,incubation time and their interaction effect(P<0.05).TVFA,acetate and valerate were significantly affected by incubation time and interaction effect of dietary NFC/NDF ratios and incubation time(P<0.01).Lactate,butyrate and isobutyrate were just significantly affected by incubation time(P<0.001).16S rRNA gene high-throughput sequencing analysis showed that bacterial community diversity was not affected by dietary NFC/NDF ratios(P>0.05),but was significantly influenced by incubation time(P<0.05).Bacterial community richness was significantly affected by incubation time(P<0.001)and interaction effect of dietary NFC/NDF ratios and incubation time(P<0.05).At the phylum level,there was no significant difference in the relative abundance of core bacteria among the three experimental groups(P>0.05).The relative abundance of dominant phyla was significantly affected by incubation time(P<0.001),but the dominant position of the core bacteria(average relative abundance more than 1%)remained unchanged.At the genus level,the relative abundance of dominant genera was not significantly affected by dietary NFC/NDF ratios(P>0.05),but was significantly influenced by incubation time(P<0.001),and the dominant position of some bacteria were changed.The relative abundance of unclassified RF16 and unclassified Christensenellaceae gradually decreased to less than 1%.However,Oribacterium and Megasphaera increased from less than 1%to more than 10%.Dialister,Butyrivibrio,Anaerovibrio and Selenomonas also increased to more than 1%with the increase of incubation time.Moreover,Prevotella and Butyrivibrio were affected by interaction effect of dietary NFC/NDF ratios and incubation time(P<0.05).Pearson correlation analysis indicated that Succiniclasticum had negative correlations with GP,TVFA,acetate,propionate,butyrate and valerate(-r>0.9,P<0.001).Oribacterium had positive correlations with GP,MCP and iso valerate(r>0.9,P<0.001).Megasphaera had positive correlations with TVFA,propionate,butyrate and valerate(r>0.9,P<0.001),but negative correlations with acetate/propionate(-r>0.9,P<0.001).In addition,a large number of unclassified bacteria were found to be closely related to rumen fermentation parameters.In conclusion,our study revealed the temporal changes and difference in the rumen fermentation parameters and bacterial microbiota,and discovered some correlations between the rumen fermentation metabolism and bacteria.However,the classification and function of some bacteria need further study.The above results showed that the proper reduction of dietary NFC/NDF ratio has no significant effect on lactation performance and blood biochemical indexes in late-lactating cows.The reasonable dietary NFC/NDF ratio(1.19)can improve antioxidant capacity and maintain the health of dairy cows.The fermentation parameters,such as GP,pH,MCP,NH3-N,propionate,iso valerate and acetate/propionate,were significantly affected by dietary NFC/NDF ratios.The bacterial community diversity and composition were not affected by dietary NFC/NDF ratios.Pearson correlation analysis showed that there were some significant correlations between rumen fermentation metabolism and some bacteria. |
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