Degradation Characteristics Of NDF From Different Pasture Sources And Its Effect On Bacterial Community Structure

Adhesion is important for forage cell walls degradation in dairy rumen, the quantitative and community structure of microbe tightly adhered in cell walls are related to the composition and structure of tissues. Cellulose, hemicellulose and pectin will be degraded by microorganism and produced lots of volatile fatty acids for dairy cows, in addition, forages are essential for rumen health and fatty acid synthesis, and also it would be decrease the opportunities of subacute ruminal acidosis. Increasing forage fiber digestibility and efficient utilization are studied as a hotspot in animal nutrition all this time. In this study, we choosed the techniques including in situ, electron microscope and high throughput sequencing and combined with animal production experiment to study the effect of forage sources on rumen fermentation, microbial protein synthesis and microorganism community in midlactation dairy cows and degradation mechanism of different forage cell walls.Exp1Effects of rumen microorganism on degradation characteristics and structure changes of different foragesThis study was conducted to investigate the degradation characteristics and structure changes of alfalfa, oat hay, leymus chinensis and rice straw stems in the rumen of dairy cows. Forage stems with similar growth and plant height were harvested and divided into two parts, one part were incubated for2h,6h,12h,24h,36h,48h and72h in the rumen, then dry matter (DM) and neutral detergent fiber (NDF) digestibilities were calculated and the other were prepared for the scanning and transmission electron microscope. The results indicated that (1) DM digestibility increased with the lapse of time, and oat hay> alfalfa> rice straw> leymus chinensis after72h degradation, the digestibility of oat hay is higher than that of alfalfa, rice straw and leymus chinensis by8.36%,20.83%and53.41%, respectively.(2) NDF digestibility increased with the lapse of time, and oat hay> rice straw> leymus chinensis> alfalfa after72h degradation, the digestibility of oat hay is higher than that of rice straw, leymus chinensis and alfalfa by5.43%,11.17%and16.17%.(3) The non-lignified tissues could be degraded quickly and completely within24h, but the lignified xylem fiber and vessels remained undegraded after72h. The mode of alfalfa degradation by rumen microorganism was dynamic bidirection, oat hay and rice straw were from the inside out, leymus chinensis was from the inside out before48h and then transfered into dynamic bidirection.(4) Cocci, bacillus and irregularly shaped bacteria were the majorities of fiber digesters, which related to the structure of tissues. The manners of adjoin, tightly adhesion and insertion were used by rumen microorganism to degrade the cell wall. The results showed that the DM and NDF digestibilities were different with each other, and cell wall composition, structure of tissue and adhesion microorganism would influence the cell wall degradation in the rumen of dairy cows.Exp2Study on the bacterial community adhered in different forage cell wallsIn this study, we used high throughput sequencing to investigate the bacterial community adhered in different forage cell walls. Alfalfa, oat hay, leymus chinensis and rice straw stems were choosed and degraded in dairy rumen for24h, then total genomic DNA were extracted for high throughput sequencing by Illumina Miseq2000. The results indicated that (1) The microbial richness indexes of the four groups were:oat hay> alfalfa> rice straw> leymus chinensis, and the microbial diversity indexes were:leymus chinensis> rice straw> oat hay>alfalfa.(2) All the sequences were assigned to16phyla,27classes,37orderes,63families and91genuses. Firmicutes, bacteroidertes, spirochaetes, fibrobacteres and proteobacteria were the highest abundance under the phyla level. The most abundant genuses were butyrivibrio, prevotella, fibrobacter and treponema in the four forages.(3) The bacterial communitis were similar within the same forages, but the different forages were various.(4) Comparison of the bacterial communities by PCoA showd that different samples would be separated effectively, PCoA with weighted UniFrac showed that PCA axis1was52.89%of the variation and PCA axis2was19.43%of the variation.(5) The group of alfalfa, oat hay, leymus chinensis and rice straw had5778,6984,5220and6018OTU respectively,2913OTU were common within groups and comprised32.38%of all the OTU. These results showed that the bacterial communities were different in the four forages.Exp3Effects of forage sources on rumen fermentation characteristics, microbial protein synthesis and bacterial community in dairy cowsEight multiparous Holstein dairy cows (632±12kg BW;135±16DIM) were used in a replicated4x4Latin square design to evaluate the effects of forage sources on rumen fermentation characteristics, microbial protein (MCP) synthesis and bacterial community. Alfalfa hay (AH), oat hay (OH), leymus chinensis (LC) and rice straw (RS) were primary sources of fiber, diets were isonitrogenous and isocaloric, and cows were fed four corn silages based total mixed rations with equivalent NDF and nonfiber carbohydrate (NFC). The results indicated that (1) Cows fed AH, OH, LC, and RS diets with equivalent NDF and NFC contents having no unfavourable effect on ruminal fermentation and MCP synthesis.(2) All the sequences were assigned to16phyla,28classes,42orderes,64families and89genuses. Bacteroidertes, firmicutes, spirochaetes and fibrobacteres were the highest abundantce under the phyla level. The most abundant genuses were prevotella, butyrivibrio, fibrobacter and treponema in the four groups.(3) Similarity of the bacterial community feeding the same diets was better under the genus level, and the genetic distance of was near in the alfalfa, oat hay and rice straw diets. The results showed that choosing different forages as fiber sources could be considered for lactation dairy cows if the NDF and NFC contents are well balanced in diets.