Abstract
Periodic feed restriction is used in cattle production to reduce feed costs. When normal feed levels are resumed, cattle catch up to a normal weight by an acceleration of normal growth rate, known as compensatory growth, which is not yet fully understood. Illumina Miseq Phylogenetic marker amplicon sequencing of DNA extracted from rumen contents of 55 bulls showed that restriction of feed (70% concentrate, 30% grass silage) for 125 days, to levels that caused a 60% reduction of growth rate, resulted in a large increase of relative abundance of Methanobrevibacter gottschalkii clade (designated as OTU-M7), and a large reduction of an uncharacterised Succinivibrionaceae species (designated as OTU-S3004). There was a strong negative Spearman correlation (ρ = -0.72, P = <1x10-20) between relative abundances of OTU-3004 and OTU-M7 in the liquid rumen fraction. There was also a significant increase in acetate:propionate ratio (A:P) in feed restricted animals that showed a negative Spearman correlation (ρ = -0.69, P = <1x10-20) with the relative abundance of OTU-S3004 in the rumen liquid fraction but not the solid fraction, and a strong positive Spearman correlation with OTU-M7 in the rumen liquid (ρ = 0.74, P = <1x10-20) and solid (ρ = 0.69, P = <1x10-20) fractions. Reduced A:P ratios in the rumen are associated with increased feed efficiency and reduced production of methane which has a global warming potential (GWP 100 years) of 28. Succinivibrionaceae growth in the rumen was previously suggested to reduce methane emissions as some members of this family utilise hydrogen, which is also utilised by methanogens for methanogenesis, to generate succinate which is converted to propionate. Relative abundance of OTU-S3004 showed a positive Spearman correlation with propionate (ρ = 0.41, P = <0.01) but not acetate in the liquid rumen fraction.
Highlights
Cattle and other domestic ruminants, such as sheep and goats, are economically important because of their ability to convert low-quality forages into high quality, high protein products suitable for human consumption [1]
Principal components analysis (PCA) of relative abundances of operational taxonomic unit (OTU) from groups R, A, RA and AA OTUs showed that, apart from 2 animals (A2 and A17), group was subjected to a restricted diet (group R) separated from group A in the first and second principal components for both liquid and solid fractions (Fig 2)
Phylogenetic amplicon sequencing showed that (i) the rumen prokaryotic communities of compensating animals at 55 days post-restriction were not significantly different from those of non-compensating animals (ii) the largest changes in relative abundance of rumen prokaryotes in feed restricted cattle compared with ad libitum cattle were an increase in the liquid fraction of the Methanobrevibacter gottschalkii clade and a strongly correlated, corresponding decrease in the liquid fraction of an uncultured Succinivibrionaceae species (OTU-S3004)
Summary
Cattle and other domestic ruminants, such as sheep and goats, are economically important because of their ability to convert low-quality forages into high quality, high protein products (milk and meat) suitable for human consumption [1] This ability is largely due to the microbial community in the rumen which is highly adapted to the breakdown and fermentation of lignocellulose, the most abundant carbon polymer on earth [2]. While used as a growth substrate by methanogens in other environments, is not metabolised to methane to any significant extent in the rumen It has been known for many years that increasing intake of highly digestible feed leads to lower methane loss per kg of feed [6]. Many of the effects of feed type and intake on rumen VFAs and consequent methane production have been known for more than 50 years, the activities of the rumen microbiota that are associated with these changes are still not fully understood
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