Effects Of Dietary Nutrient Levels On The Bacterial Flora,pH And VFA Levels In Rumen Of Tan Sheep

Tan sheep in the Ningxia Hui Autonomous Region were famous for their Ermao fur and fresh meat.However,because of the deterioration of ecological environments in recent years,ruminant farming systems had become dominated by indoor systems instead of traditional grazing systems mainly.As the farming system had transformed,the feedstuff types had changed.At present,few studies were related to rumen fermentation,especially on rumen bacterial community associated with different levels(energy and protein levels)of dietary energy and protein in Tan sheep.The primary objective of this study was to compare the effects of different days of age and levels of dietary nutrient on the diversity of rumen bacteria,pH and VFA in Tan sheep.A total of 112 healthy Tan sheep(half male and half female,aged 105 days)with an average initial body weight(BW)of 36±1.35 kg were used in this study.They were randomly allotted to one of four dietary treatments(Group I,II,III and IV).Each treatment included 4 replicated pens,with 7 sheep in each(total of 28 sheep in each treatment).From Group I to IV,energy of diets were 7.08 MJ· kg-1,8.09 MJ· kg-1,9.10 MJ· kg-1 and 10.11MJ· kg-1,respectively;dietary protein levels were 8.04%,9.19%,10.34% and 11.49%,respectively.The ratio of energy to protein was kept unchanged(about 0.88).The experiment lasted for 75 days,including 15 days for adaptation.On the day of slaughter(150 and 180 days of age),one sheep was randomly selected from each replicated pen per treatment(a total of 4 sheep were selected per treatment)was slaughtered and rumen contents were collected,pH and VFA levels in the rumen were analyzed.Genomic DNA was extracted from rumen contents,a part of the DNA was used for the absolute quantification of these related microbes by qRT-PCR analysis,another part of the DNA was used for investigating the structure of rumen bacterial community and predicting the related functions by the next-generation sequencing strategy.The results of this study were showed as follow:1.On the 150 and 180 days of age,the number of S.ruminantium were significantly different(P<0.05).With the increasing levels of dietary nutrient,the number of P.ruminicola,R.flavefaciens and S.dextrinisolvens demonstrated the tendencies to increase(P<0.05).Additionally,according to the correlated analytic method,these different rumen bacteria at species level had mutual promoted effects.2.pH was no change with different days of age and levels of dietary nutrient(P>0.05).However,different dietary nutrient levels had significantly effects on the content of VFA.Among them,the content of acetate acid showed the significant tendencies to decrease with thie increasing dietary nutrient levels(P<0.05).Ratio of butyrate,isobutyric,pentanoic acid and isovaleric to total volatile fatty acid(TVFA)showed the significant tendencies to upward(P<0.05).The ratio of propionic acid was significantly and positively correlated with the number of V.parvula(r = 0.42,P<0.05),while the content of pentanoic acid was extremely significantly negatively related to the number of V.parvula(r=-0.53,P<0.01).3.The study observed 133 genera belonging to 16 phyla distributed throughout the rumen samples.With Firmicutes,Bacteroidetes and Proteobacteria predominating.Additionally,the higher nutritional dietary level linearly increased(P<0.05)the number of Bacteroidetes and Proteobacteria but linearly decreased(P<0.05)the Firmicutes richness.With the increasing of dietary nutrient levels,the ratio of Butyrivibrio,Saccharofermentans and Pseudobutyrivibrio showed significantly downward trends(P<0.05),while the ratio of Prevotella,Prevotellaceae_uncultured and Succinivibrio showed significantly upward trends(P<0.05).Furthermore,with the predicted the potential functions of rumen bacteria,we found the relative abundances of the genes related to carbohydrates were overrepresented,and the genes involved in amino acid metabolism linearly increased(P<0.05).In conclusion,compared with the effect of days of age,different nutrient levels have greater effects on rumen bacteria and VFA levels.The numbers of rumen bacteria at phylum,genus and species were significantly different with the increasing levels of dietary nutrient.Furthermore,we predicted the potential functions of gene families within rumen bacteria.These findings provide the first deep insights into the rumen bacterial composition and the targeted improvement of dietary protein and energy use efficiency in Tan sheep.