Abstract
This study presents the application of metabolomics to evaluate changes in the rumen metabolites of beef cattle fed with three different diet types: forage-rich, mixed and concentrate-rich. Rumen fluid samples were analysed by 1H-NMR spectroscopy and the resulting spectra were used to characterise and compare metabolomic profiles between diet types and assess the potential for NMR metabolite signals to be used as proxies of methane emissions (CH4 in g/kg DMI). The dataset available consisted of 128 measurements taken from 4 experiments with CH4 measurements taken in respiration chambers. Predictive modelling of CH4 was conducted by partial least squares (PLS) regression, fitting calibration models either using metabolite signals only as predictors or using metabolite signals as well as other diet and animal covariates (DMI, ME, weight, BW0.75, DMI/BW0.75). Cross-validated R2 were 0.57 and 0.70 for the two models respectively. The cattle offered the concentrate-rich diet showed increases in alanine, valerate, propionate, glucose, tyrosine, proline and isoleucine. Lower methane yield was associated with the concentrate-rich diet (p < 0.001). The results provided new insight into the relationship between rumen metabolites, CH4 production and diets, as well as showing that metabolites alone have an acceptable association with the variation in CH4 production from beef cattle.
Highlights
Livestock production is the largest anthropogenic contributor to the global CH4 budget (103 [95–109] Tg CH4 yr−1 during 2000–2009)[1], with enteric CH4 emissions being the largest contributors to this (87–97 Tg CH4 yr−1 during 2000–2009)[1,2,3]
In the field of metabolomics there are 3 main analytical techniques used: nuclear magnetic resonance (NMR), gas chromatography coupled with mass spectrometry (GC-MS), and liquid chromatography coupled with mass spectrometry (LC-MS)[15]
The use of 1H-13C correlated experiments in this analysis was necessary as many 1H resonances overlap at 600 MHz and their identity in 1D 1H NMR spectra is obscured
Summary
Livestock production is the largest anthropogenic contributor to the global CH4 budget (103 [95–109] Tg CH4 yr−1 during 2000–2009)[1], with enteric CH4 emissions being the largest contributors to this (87–97 Tg CH4 yr−1 during 2000–2009)[1,2,3]. This was thought to be the sole pathway for CH4 production Another group of methanogens uses methyl-containing metabolites such as methanol and methylamine to produce CH4, utilising the methylotrophic methanogenic pathway[10]. This pathway is found in the Thermoplasmata genus of archaea showing enhanced growth when given methylamine supplements. The objectives of this work were to identify NMR signals and related metabolites associated with the different diets, with particular interest in metabolites belonging to the methylotrophic pathway, methanol and methylamine, and assess the possibility of using these signals as a proxy for ruminant CH4 emissions
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