TY  - THES
T1  - Studies on the composition of the ruminal microbial community using grass silage and corn silage
A1  - Lengowski,Melanie
Y1  - 2018/02/12
N2  - Grass silage and corn silage are the most commonly used silages for feeding dairy cows and fattening bulls. Due to their different chemical composition these silages have diverse effects on the ruminal microbial community and, therefore, on the fermentation process in the rumen. The major objective of this thesis was to evaluate the effect of grass silage and corn silage on the ruminal microbial community composition. The focus was on the incubation of silages without using concentrates. Furthermore, diurnal changes of the ruminal microbial community were investigated.
In the first study (Manuscript 1), effects of incubation of grass silage and corn silage on the ruminal microbial community were investigated using an established rumen simulation technique (Rusitec). Furthermore, diurnal changes and changes during the first 48 hours of incubation (adaption phase) were observed. A significant decrease of the complete ruminal microbial community in the fermenter liquids, on species and group level, was observed. During the adaption phase, the silage source lost relevance because in the silage-containing fermenters as well as in the blank fermenters decreasing numbers were observed with the exception of Clostridium aminophilum. For this species, after 48 hours higher numbers were found as compared to the inoculum. As has already been described in the literature, in the current thesis changes in microbial abundance were lesser in feed residues than in fermenter liquids. The abundance of protozoa in feed residues decreased during the first 48 hours while for Prevotella bryantii and C. aminophilum higher numbers were found after 24 and 48 hours as compared to the inoculum. The adaption in the Rusitec had not yet been fully completed after 48 hours, since for several species a different abundance was found on day 13 of incubation (Period 2). The provision of fresh substrate at the beginning of Period 2 led to an increase of almost all species and groups within the following two to four hours, with the exception of the protozoa and methanogens. The reduction of the protozoal population and methanogens could have been the result of migration from fermenter liquids to new feed particles and also the fact that some species of methanogens are associated to protozoa. Likewise, sampling of the feed residues after 24 and 48 hours was too late since the microorganisms could have been already detached. However, sampling of the feed residues at shorter intervals is not possible in the Rusitec. No effect of silage was observed on the abundance of total bacteria, methanogens and Selenomonas ruminantium. Methanogens and S. ruminantium do not use the substrate itself but rather fermentation end products of other ruminal microorganisms. Although no effect of silage was observed on the abundance of methanogens, more methane was produced during the incubation of grass silage than corn silage. This is in accordance with results described in literature that an abundance of methanogens is not associated with the production of methane. The corn silage promoted the abundance of protozoa and Ruminobacter aminophilus whereby the latter could only be detected during the first 48 hours of incubation. Quantification was not possible because of the generation of unspecific products during real-time qPCR. Fibrobacter succinogenes was also promoted by corn silage even though this is one of the most active cellulolytic species in the rumen. It could be possible that this species had an advantage in the degradation of the cell wall structures of C4 plants (which corn accounts to) as compared to other cellulolytic species. The grass silage promotes the abundance of the cellulolytic Ruminococcus albus as well as P. bryantii and C. aminophilum. The last two species use amino acids and proteins as energy sources thereby the latter belongs to hyper ammonia producing bacteria which could be the reason for the higher ammonia concentration in fermenter liquids during the incubation of grass silage compared to corn silage. 
In the second study (Manuscript 2), the effects of supplementing corn silage with different nitrogen sources on ruminal microbial community composition and ruminal microbial crude protein synthesis was investigated. Higher efficiency of microbial crude protein synthesis with corn silage has been reported from in vivo studies, while in vitro contradictory results were found. It was proposed that the different nitrogen content of the silages, and especially the lack of rumino-hepatic circulation in vitro, could be the reason for the lower efficiency of microbial crude protein synthesis when using corn silage. Different microbial species prefer different nitrogen sources as already observed in pure cultures and partially also in mixed cultures. Thus, in the second study, corn silage was supplemented with urea, pea protein, pea peptone or mixed free amino acids. With the supplementation of peptone and urea to corn silage, the highest efficiency of microbial crude protein synthesis was observed followed by amino acids and protein supplementation. But none of the used nitrogen sources allowed corn silage to achieve the level of microbial crude protein synthesis observed for grass silage. The protozoal population was negatively correlated with the efficiency of microbial crude protein synthesis which could have been a result of the higher energy requirement of protozoa compared to bacteria. Furthermore, protozoa engulfs and ingests bacteria and uses it as the main energy and protein source which could also have a negative effect on the efficiency of microbial crude protein synthesis. The effects of different nitrogen sources on the abundance of microbial groups and species not always were in accordance with reports in the literature. This could be attributed to the use of different substrate and pure cultures. 
In the third study (Manuscript 3), the effect of grass silage and corn silage on the ruminal microbial community composition in vivo was investigated. Three lactating Jersey cows fitted with a permanent cannula were fed with rations based on grass silage or corn silage. The rations contained the same amount of concentrate. In order to adjust the nitrogen content of the rations the corn silage based ration was supplemented with urea. The corn silage based ration promoted the abundance of total bacteria in the solid fraction obtained from the rumen, as well as the protozoal population in the solid and liquid fraction. It could be possible that the higher content of readily fermentable carbohydrates, mainly starch, of the corn silage in combination with the urea could have had a positive effect on both groups. Furthermore, a higher abundance of F. succinogenes was observed in animals fed with the corn silage-based ration. As expected, the cellulolytic bacteria R. albus and R. flavefaciens were enhanced by the grass silage-based ration as well as P. bryantii and R. amylophilus. The latter are known to use starch and maltose as energy source and to use their proteolytic activity only to achieve access to protein-coated starch. It is assumed that the combination of grass silage and concentrate could have had an influence on this species. For S. ruminantium, a feeding effect on the abundance was only observed in the liquid fraction while in the solid fraction no effect was found. There was also no observable effect of ration on the abundance of C. aminophilum, RCC and the methanogens. Changes of the ruminal microbial community over time were observed. But no consistent increase of all species and groups after the phase with the highest dry matter intake of fresh feed became obvious. 
In conclusion, the results of the current thesis showed that grass and corn silages differently affected the composition of the ruminal microbial community in the liquid and solid fractions of the rumen content. Furthermore, significant diurnal changes of the ruminal microbial community could be observed in vitro as well as in vivo. These results highlighted the need of repeated sampling during the day and suggest the consideration of both ruminal compartments, liquid and solid.

KW  - Pansen
KW  - Grassilage
KW  - Maissilage
CY  - Hohenheim
PB  - Kommunikations-, Informations- und Medienzentrum der Universität Hohenheim
AD  - Garbenstr. 15, 70593 Stuttgart
UR  - http://opus.uni-hohenheim.de/volltexte/2018/1435
ER  -