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Pasture Feeding Changes the Bovine Rumen and Milk Metabolome
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2018-04-06
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O’Callaghan, T.F.; Vázquez-Fresno, R.; Serra-Cayuela, A.; Dong, E.; Mandal, R.; Hennessy, D.; McAuliffe, S.; Dillon, P.; Wishart, D.S.; Stanton, C.; Ross, R.P. Pasture Feeding Changes the Bovine Rumen and Milk Metabolome. Metabolites 2018, 8, 27. https://doi.org/10.3390/metabo8020027
Abstract
The purpose of this study was to examine the effects of two pasture feeding
systems—perennial ryegrass (GRS) and perennial ryegrass and white clover (CLV)—and an indoor
total mixed ration (TMR) system on the (a) rumen microbiome; (b) rumen fluid and milk metabolome;
and (c) to assess the potential to distinguish milk from different feeding systems by their respective
metabolomes. Rumen fluid was collected from nine rumen cannulated cows under the different
feeding systems in early, mid and late lactation, and raw milk samples were collected from ten
non-cannulated cows in mid-lactation from each of the feeding systems. The microbiota present in
rumen liquid and solid portions were analysed using 16S rRNA gene sequencing, while 1H-NMR
untargeted metabolomic analysis was performed on rumen fluid and raw milk samples. The rumen
microbiota composition was not found to be significantly altered by any feeding system in this study,
likely as a result of a shortened adaptation period (two weeks’ exposure time). In contrast, feeding
system had a significant effect on both the rumen and milk metabolome. Increased concentrations of
volatile fatty acids including acetic acid, an important source of energy for the cow, were detected in
the rumen of TMR and CLV-fed cows. Pasture feeding resulted in significantly higher concentrations
of isoacids in the rumen. The ruminal fluids of both CLV and GRS-fed cows were found to have
increased concentrations of p-cresol, a product of microbiome metabolism. CLV feeding resulted in
increased rumen concentrations of formate, a substrate compound for methanogenesis. The TMR
feeding resulted in significantly higher rumen choline content, which contributes to animal health
and milk production, and succinate, a product of carbohydrate metabolism. Milk and rumen-fluids
were shown to have varying levels of dimethyl sulfone in each feeding system, which was found to
be an important compound for distinguishing between the diets. CLV feeding resulted in increased
concentrations of milk urea. Milk from pasture-based feeding systems was shown to have significantly
higher concentrations of hippuric acid, a potential biomarker of pasture-derived milk. This study
has demonstrated that 1H-NMR metabolomics coupled with multivariate analysis is capable of
distinguishing both rumen-fluid and milk derived from cows on different feeding systems, specifically
between indoor TMR and pasture-based diets used in this study.