Bacterial Community Diversity Associated With Different True Digestibility Of Dietary Phosphorus In The Gastrointestinal Tract Of Goat

Phosphorus not only plays an important biological role in the formation and growth of animal skeleton,but also was an expensive feed material.However,the utilization rate of phosphorus was low in plant feed.It will eventually cause serious soil and water pollution because of the undigested phosphorus was discharged into the environment through feces.Therefore,raising the animal's digestibility of feed phosphorus was not only beneficial to animal production,but also can save the cost of feeding.It was well known that ruminants digest nutrients differently from monogastric animals because of their special physiological structure.Their digestion of nutrients depends on microbial digestion.Therefore,microorganisms may be one of the factors affecting the digestibility and utilization of phosphorus in ruminant feed.So far,there were no reports on the relationship between gastrointestinal microorganisms and phosphorus digestion and utilization in ruminants.In view of this,the relationship between gastrointestinal microbial diversity and goat feed phosphorus digestibility was explored for the first time in this experiment.Twenty-eight Nubian black goats with the same breed,age,sex and feeding management were used as experimental animals.The whole experiment period totaling 40 days,of which consisted of two stages?stage I and II?,each experiment lasted for 20 days,which consisted of 14 days pre-feeding period and 6 days digestion test period.In addition to the addition of CaCO₃ and CaHPO₄ in the first trial diet to meet the requirements of the differential method?the total phosphorus content were0.33 and 0.22 in the first and second trial?,the ratio of calcium and phosphorus?the ratio of calcium and phosphorus were 1.58 and 1.59 in the first as well as second trial diet?,and the composition of the diet were basically the same.The goats fed the same total mixed diet during the digestion test period?the ratio of concentrate and roughness=45:55?,fed in a single cage,and collected all the feces and urine excreted by all goats every day.In addition,the daily feeding amount and surplus of each goat were recorded.After digestion test,slaughter test was carried out.The contents of rumen,true stomach,jejunum,cecum and colon were taken and stored in sterile EP tube at-80?.The mean and standard deviation of true phosphorus digestibility were calculated according to data of the digestion test.Then the goats with true phosphorus digestibility>mean+0.5*standard deviation were selected as the high phosphorus digestibility group?HP?and the goats with true phosphorus digestibility<mean-0.5*standard deviation were selected as the low phosphorus digestibility group?LP?.The gastrointestinal contents of 16 experimental animals in HP?n=8?and LP group?n=8?were selected to extract total microbial DNA.High variable region of bacterial16S rRNA genes was amplified as well as analyzing amplicon sequence data on the Illumina MiSeq sequencing platform and biological information analysis using QIIME software were done.The data of HP group and LP group were tested for significance.The results show that:1).The true phosphorus digestibility of feed of the 28 goats was highly variation across the individual goats?from 68.38%to 92.82%with a coefficient of variation?CV?of 8.17%;mean:83.28%±6.81%?.The average true digestibility of phosphorus of HP and LP groups were 89.45%±2.86%and 78.42%±1.21%?mean±SD?,respectively,with significant difference between groups?P<0.01?.In addition,the blood phosphorus content of goats in HP group was significantly higher than that of LP group?P<0.05?.2).At the phylum level,the dominant phylum of rumen and abomasum were similar,among which Bacteroidetes was the most abundant?rumen:HP 62.84%,LP58.43%;abomasum:HP 45.10%,LP 44.28%?,followed by Firmicutes?rumen:HP29.44%,LP 33.20%;abomasum:HP 29.44%,LP 33.20%?.The dominant phylum of colon,cecum and jejunum were similar.The dominant phylum of jejunum?HP66.69%,LP 62.22%?,colon?HP 66.22%,LP 59.35%?and cecum?HP 64.92%,LP54.05%?were Firmicutes,followed by Bacteroides.3).The relative abundance of Firmicutes in LP group?30.70%?was significantly higher than that in HP group?22.55%?at the phylum level?P<0.05?,and the relative abundance of Verrucomicrobia,Lentisphaerae and Firmicutes in colon LP group was significantly higher than that in HP group?P<0.05?.At the genus level,there were 11bacterial genera had significant differences of rumen HP and LP groups,and the relative abundance of 8 bacterial genera in LP group?Ruminococcaceae_UCG-010;Ruminococcus₂;Ruminococcaceae_NK4A214_group;Ruminococcaceae_UCG-014;Prevotella₁;Saccharofermentans;Mogibacterium;Eubacterium and Fanody?was significantly higher than that in HP group?P<0.05?,and The relative abundance of three bacterial genera?slenomonas₁,Treponema₂ and Prevotella?was significantly lower than that of HP?P<0.05?.There were 12 genera had significant differences of abomasum in HP group and LP group,among which 12 genera in LP group?Rikenellaceae_gut_group,Lachnospiraceae_ND3007_group,Saccharofermentans,Ruminococcus₁,Eubacterium_coprostanoligenes_group,Ruminococceae_UCG-014,Lachnospiraceae_XPB1014_group,Desulfocloso,Lachnotrium₁0,Anchoragax,Pavoracter,Ruminococca The relative abundance of ceae_UCG-004 and Oscillospira was significantly higher than that of HP?P<0.05?.The relative abundance of five bacterial genera of jejunum?Prevotella,Rikenellaceae_RC9_gut_group,Fibrobacter,Desulfovibrio and Lostridium_sensu_stricto₁?in LP group was significantly lower than that in HP group?P<0.05?,and the relative abundance of two genera?Victivallis and Ruminococcus₂?was significantly higher than that in HP group?P<0.05?.In colon,the relative abundance of Victivallis and Ruminococcaceae_UCG-014 in LP group was significantly higher than that in HP group.The relative abundance of Desulfovibrio of cecum in LP group was significantly lower than that in HP group?P<0.05?.4?.The correlation analysis between the true digestibility of feed phosphorus and the relative abundance of microorganisms showed that the true digestibility of phosphorus was negatively correlated with the relative abundance of Ruminococcaceae_UCG-010,Ruminococcus₂ and Ruminococcaceae_UCG-014 in the rumen,and positively correlated with Selenomonas₁ and Prevotella.The true digestibility of phosphorus was positively correlated with 10 bacteria in the true stomach?Lachnospiraceae,Saccharofermentans,Ruminococcus₁,Eubacterium,Ruminococcaceae,Lachnospiraceae_XPB1014,Desulfovibrio,Anaerovorax and Papillibacter?.The true digestibility of phosphorus was negatively correlated with the relative abundances of Prevotella and Lostridium_sensu_stricto₁ of jejunum,and was positively correlated with Fibrobacter,Desulfovibrio,Victivallis and Ruminococcus₂.There was a significant positive correlation with the relative abundance of Victivallis and Ruminococcaceae_UCG-014 of colon,and a significant positive correlation with the relative abundance of Desulfovibrio in the cecum.In summary,this study found that there were significant individual differences in the true digestibility of phosphorus in goats feed.There were significant differences in the structure of microorganisms in rumen,abomasum,jejunum,cecum and colon of goats with high and low true digestibility of phosphorus.The relative abundance of microorganisms in the abomasum was the most significant difference among the groups,followed by the rumen,jejunum,colon and cecum.There were microorganisms in different gastrointestinal segments which were significantly correlated with the true phosphorus digestibility of feedstuffs.The number of microorganisms which were significantly positively correlated with the true phosphorus digestibility of feedstuffs was the largest in the abomasum,followed by the rumen.Gastrointestinal microorganisms may be one of the factors affecting the phosphorus digestibility of goat diets.