Ruminal bacterial community is associated with the variations of total milk solid content in Holstein lactating cows

Total milk solid(TMS)content directly reflects the quality of milk.Rumen bacteria ferment dietary components,the process of which generates the precursors for the synthesis of milk solid,therefore,the variation in rumen bacterial community could be associated with milk solid in dairy cows.In this study,45 healthy mid-lactation Holstein dairy cows with the similar body weight,lactation stage,and milk yield were initially used for the selection of 10 cows with high TMS(HS)and 10 cows with low TMS(LS).All those animals were under the same feeding management,and the individual milk yield was recorded for 14 consecutive days before milk and rumen fluid were sampled.Rumen fluid was used to determine bacterial community by 16S rRNA gene sequencing technique.The HS cows had significantly greater feed intake and milk TMS,fat,protein content than LS cows(P<0.05).Among the volatile fatty acids(VFA),propionic acid and valeric acid concentrations were significantly greater in HS cows than those in LS cows(P<0.05).There was no significant difference in the concentrations of acetate,butyrate,isobutyrate,valerate,and the total VFA(P>0.05),nor was the acetate-to-propionate ratio,pH value,ammonia nitrogen and microbial crude protein concentrations(P>0.05).Significant differences in the relative abundances of some bacterial genera were found between HS and LS cows.Spearman’s rank correlation analysis revealed that TMS content was correlated positively with the abundances of Ruminococcaceae UCG-014,Ruminococcaceae NK4A214 group,Prevotellaceae UCG-001,Butyrivibrio 2,Prevotellaceae UCG-003,Candidatus Saccharimonas,Ruminococcus 2,Lachnospiraceae XPB1014 group,probable genus 10,Eubacterium ventriosum group,but negatively correlated with Pyramidobacte.In addition,Ruminococcaceae UCG-014,Ruminococcus 2,Ruminococcaceae UCG001,probable genus 10 and Eubacterium ventriosum group might boost the total VFA production in the rumen.In conclusion,the dry matter intake of dairy cows and some special bacteria in rumen were significantly associated with TMS content,which suggests the potential function of rumen bacteria contributing to TMS content in dairy cows.

Sewage sludge disintegration by high-pressure homogenization: A sludge disintegration model

High-pressure homogenization （HPH） technology was applied as a pretreatment to disintegrate sewage sludge. The effects of homogenization pressure, homogenization cycle number, and total solid content on sludge disintegration were investigated. The sludge disintegration degree （DDCOD）, protein concentration, and polysaccharide concentration increased with the increase of homogenization pressure and homogenization cycle number, and decreased with the increase of sludge total solid （TS） content. The maximum DDCOD of 43.94% was achieved at 80 MPa with four homogenization cycles for a 9.58 g/L TS sludge sample. A HPH sludge disintegration model of DDCOD= kNaPb was established by multivariable linear regression to quantify the effects of homogenization parameters. The homogenization cycle exponent a and homogenization pressure exponent b were 0.4763 and 0.7324 respectively, showing that the effect of homogenization pressure （P） was more significant than that of homogenization cycle number （N）. The value of the rate constant k decreased with the increase of sludge total solid content. The specific energy consumption increased with the increment of sludge disintegration efficiency. Lower specific energy consumption was required for higher total solid content sludge.