| The study was conducted to investigate effects of dietary non-fiber carbohydrate to neutral detergent fiber?NFC/NDF?ratio on rumen microbes,nutrition digestibility and rumen fermentation characters to provide data support for the formulation of diets which can improve rumen environment,the utilization of nutrients,and to provide scientific guidance for the application and popularization of dietary NFC/NDF ratio on the production of ruminants.The study was designed as a feeding experiment,including 15 days of pre-feeding period and 113 days for feeding period.Sample collection in feeding period were divided into four stages,stage??117 d,age of 12 to 13 months?,stage??3349 d,age of 13 to 14 months?,stage??6581 d,age of 14 to 15 months?and stage??97113 d,age of 15 to 16 months?,and each stage included17 d.The digestion tests were conducted at day 1 to day 8 to measure the apparent digestibility of nutrients and to predict methane emissions in each stage;Rumen fluid was collected at different time points in day 9 to day 11 consecutively to analyze rumen fermentation characters in each stage;Rumen fluid was collected before morning feeding in day 15 to day 17 consecutively to determine the composition and structure of rumen bacteria and archaea by high-throughput sequencing method.Fasting weighs were conducted on test animals before pre-feeding period and after sampling in each stage to measure average daily gain?ADG?.Finally,the data of nutrient digestibility,ADG,predicted methane emissions,rumen fermentation characters and rumen microbes in four stages were classified and integrated to investigate effects of dietary NFC/NDF ratio on the digestion,rumen fermentation and rumen microbes in Karakul sheep.The whole experiment was divided into the following three parts:Part 1:Effects of dietary NFC/NDF ratio on digestion,ADG and the predicted methane emission in Karakul sheepThe experiment was conducted to investigate effects of dietary NFC/NDF ratio on digestion,ADG and methane emission?predicted?in Karakul sheep to provide data support for formulating the feed structure to improve nutrient utilization and to reduce methane emissions.Twelve Karakul wether with good health and fitted with permanent rumen fistula were divided into four groups according to the principle of similar weight?35±3.3 Kg?and age?12 month?,each group with three replicates.Four kinds of dietary NFC/NDF ratio of 0.54,0.96,1.37 and 1.90 were formulated to feed Karakul sheep?limited feeding?as group 1,group 2,group 3 and group 4.The total feces collection method was used to measure the apparent nutrition digestibility in day 1 to day 8 in each stage;Fasting weighs were conducted on test animals before pre-feeding period and after sampling in each stage to measure ADG;The methane emission,and the methane emission of unit nutrition intake and unit metabolic body weight were predicted according to the model:CH4?L/d?=-26.94×NFC/NDF+90.71?R2=0.665?.Results showed that:?1?The apparent digestibility of dry matter?DM?in four stages were that:group 3>group 4>group 2>group 1,and the difference were significant?P<0.05?.?2?The apparent digestibility of organic matter?OM?in stage?was that:group 4>group 3>group 2>group 1,and the difference was significant?P<0.05?.While it was the highest in group 3 in stage?,?and?,and the difference were not significant?P>0.05?.?3?The apparent digestibility of NDF and acid detergent fiber?ADF?were the highest in group 3,and no significant difference was found in four stages?P>0.05?.?4?The ADG were that:group 3>group 4>group 2>group 1,and it was significant in stage?and the whole stage?P<0.05?.?5?According to the model,the predicted methane emission were 76.16,64.85,53.80 and 39.52 L/d as dietary NFC/NDF ratio were 0.54,0.96,1.37 and 1.90,respectively.When Karakul sheep were feed with limitation,the predicted methane emission of unit dry matter intake?DMI?and organic matter intake?OMI?intake were that:group 1>group 2>group 3>group 4 in four stages,and the difference were significant?P<0.05?.When limited feeding,the predicted methane emission of unit non detergent fiber?NDFI?and acid detergent fiber intake?ADFI?were the lowest in group 4 in four stages,and the difference were significant?P<0.05?.When limited feeding,the predicted methane emission of unit metabolic body wight were that:group 1>group 2>group 3>group 4 in four stages,and the difference were significant?P<0.05?.Taken together,the nutrition apparent digestibility and ADG of Karakul sheep were the highest in dietary NFC/NDF ratio of 1.37.When limited feeding,the predicted methane emission decreased significantly in dietary NFC/NDF ratio of 1.37 and 1.90.Part 2:Effects of dietary NFC/NDF ratio on rumen fermentation in Karakul sheepThe study investigated effects of dietary NFC/NDF ratio on rumen fermentation characters to provide data support for formulating feed structure to improve rumen environment.Experimental animals,diets and group were divided as Part 1.The study was conducted in day 9 to day 11consecutively in each stage,and rumen fluid were collected at 0,1,3,6 and 9 h after feeding for50 mL,respectively,to measure ruminal pH,NH3-N and sodium cellulolytic enzyme activity,and the final results of each indicator were based on the average of time points.The results showed that:?1?The average pH in four stages were that:group 1>group 2>group 3>group 4,and the difference were significant?P<0.05?.?2?The average concentration of NH3-N in four stages were the highest in group 3,and the difference weren't significant?P>0.05?.?3?The average enzyme activity of sodium carboxymethylcellulose?CMC?was not significant in stage??P>0.05?,while it were that:group 1>group 2>group 3>group 4 in other stages,and the difference were significant?P<0.05?.The average enzyme activities of glucoside and xylan in stage?,?and?were that:group 2>group 1>group 3>group 4,and the difference were significant?P<0.05?.In conclusion,the ruminal pH decreased with the increase of dietary NFC/NDF ratio,and the concentration of NH3-N was higher in dietary NFC/NDF ratio of 1.37,and the average enzyme activities of CMC,glucoside and xylan were higher in dietary NFC/NDF ratio of 0.54 and 0.96.Part 3:Effects of dietary NFC/NDF ratio on rumen bacteria and methanogens in Karakul sheepBy studying the effects of dietary NFC/NDF ratio on rumen bacteria and archaea,the experiment was aimed to provide reference for improving rumen fermentation,nutrient digestibility,and excavating rumen microbial resources in Karakul sheep.The experiment animals,diets and experimental groups were the same as Part 1.Rumen fluid was collected before morning feeding in day 15 to day 17 in each stage for 50 mL,respectively.The three generations of full-length amplifiers sequencing and 16S rDNA sequencing method were used to investigate rumen bacteria and archaea,respectively.Results were as following,bacteria:?1?The bacteria diversity in dietary NFC/NDF ratio of 1.90 was decreased in stage?and?.?2?At phylum level,Bacteroidetes and Firmicutes were the most dominant bacteria,and their relative abundance was37%60%and 26%51%,respectively.Dietary NFC/NDF ratio had no significant difference in the relative abundance of Bacteroidetes,Firmicutes,Tenericutes and Spirochaete?P>0.05?.?3?At genus level,the relative abundance of unidentifiedLachnospiraceae was that:group 3>group4>group 1>group 2 in stage?,while it was:group 3>group 1>group 4>group 2 in stage?,and the difference were significant?P<0.05?.The relative abundance of Mycoplasma was higher in group 4 and lower in group 2 in stage?,and the difference was significant?P<0.05?.The relative abundance of Succiniclasticum was found higher in group 2 in stage??P<0.05?.Lactobacillus was low in abundance,and difference was not significant?P>0.05?.?4?At species level,the main semi-cellulose degrading and starch-degrading were low in abundance,and there was no difference in four stages?P>0.05?.?5?The rumen bacteria structure changed largely in dietary NFC/NDF ratio of 0.96 with the prolongation of feeding time.Archaea:?1?The diversity of rumen archaea decreased in dietary NFC/NDF ratio of 1.90 in four stages.?2?At genus level,Methanobrevibacter was the most dominant genus,and its relative abundance were the highest in group 4 in stage?,?and?,and the differences were not significant?P>0.05?.?3?According to Beta diversity index,the archaea structure changed larger between group 2 and group 4 with the prolongation of feeding time.?4?At species level,the relative abundance of Methanobrevibactermillerae,Methanobrevibacterwolinii and MethanosphaeraspISO3F5 in four stages were that:group 4>group 3>group 1>group 2,while the relative abundance of Methanobrevibacterruminantium was that:group 2>group 3>group 4>group 1,and the differences were significant?P<0.05?.The relative abundance of Butyrivibriofibrisolvens was ranked as:group 1>group 3>group 4>group 2 in stage?,while it was ranked as:group 3>group1>group 4>group 2 in stage?,and the difference were significant?P<0.05?.The relative abundance of Ruminococcusflavefaciens,RuminococcusspFC2018 and Ruminococcusalbus were low in abundance,and the difference were not significant?P>0.05?.Taken together,the effects of dietary NFC/NDF ratio on rumen bacteria and archaea in Karakul sheep was regular with the prolongation of feeding time.The relative abundance of semi-cellulose degrading genus and cellulose degrading were higher in dietary NFC/NDF ratio of 1.37 with the prolongation of feeding time.The relative abundance of methanogens were higher in dietary NFC/NDF ratio of1.90 in the whole feeding time.ConclusionRumen microbe has a certain adaptability to the feeding structure with the prolongation of feeding time.The relative abundance of semi-cellulose degrading genus and cellulose-degrading species,ADG,and the apparent digestibility of cellulose were the highest in dietary NFC/NDF ratio of 1.37,and the predicted methane emission was lower in dietary NFC/NDF ratio of 1.37.Thus,dietary NFC/NDF ratio of 1.37 can improve nutrition digestibility,rumen fermentation,and decrease the methane emission. |
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