Abstract
Frothy bloat is a serious metabolic disorder that affects stocker cattle grazing hard red winter wheat forage in the Southern Great Plains causing reduced performance, morbidity, and mortality. We hypothesize that a microbial dysbiosis develops in the rumen microbiome of stocker cattle when grazing on high quality winter wheat pasture that predisposes them to frothy bloat risk. In this study, rumen contents were harvested from six cannulated steers grazing hard red winter wheat (three with bloat score “2” and three with bloat score “0”), extracted for genomic DNA and subjected to 16S rDNA and shotgun sequencing on 454/Roche platform. Approximately 1.5 million reads were sequenced, assembled and assigned for phylogenetic and functional annotations. Bacteria predominated up to 84% of the sequences while archaea contributed to nearly 5% of the sequences. The abundance of archaea was higher in bloated animals (P < 0.05) and dominated by Methanobrevibacter. Predominant bacterial phyla were Firmicutes (65%), Actinobacteria (13%), Bacteroidetes (10%), and Proteobacteria (6%) across all samples. Genera from Firmicutes such as Clostridium, Eubacterium, and Butyrivibrio increased (P < 0.05) while Prevotella from Bacteroidetes decreased in bloated samples. Co-occurrence analysis revealed syntrophic associations between bacteria and archaea in non-bloated samples, however; such interactions faded in bloated samples. Functional annotations of assembled reads to Subsystems database revealed the abundance of several metabolic pathways, with carbohydrate and protein metabolism well represented. Assignment of contigs to CaZy database revealed a greater diversity of Glycosyl Hydrolases dominated by oligosaccharide breaking enzymes (>70%) in non-bloated samples. However, the abundance and diversity of CaZymes were greatly reduced in bloated samples indicating the disruption of carbohydrate metabolism. We conclude that mild to moderate frothy bloat results from tradeoffs both within and between microbial domains due to greater competition for substrates that are of limited availability as a result of biofilm formation.
Highlights
Grazing winter wheat by beef cattle on the Southern Great Plains of the US is routinely practiced during late fall (November) through spring each year (Horn et al, 1981; Pinchak et al, 1996; Min et al, 2005, 2006; Horn, 2006; Sij et al, 2007)
We have reported that stocker cattle, when transitioned from a hay diet to a winter wheat forage diet, exhibited a significant shift in rumen microbial communities with an increase in Bacteroidetes and reduction in Firmicutes (Pitta et al, 2010)
As recent evidences indicate that the composition of rumen microbes is directly related to the health and production performance of cattle (McCann et al, 2014; Morgavi et al, 2015), we sought to investigate changes in the microbial ecology and functional potential of the rumen microbiome and fermentation pattern in the rumen of stocker cattle that succumbed to bloat
Summary
Grazing winter wheat by beef cattle on the Southern Great Plains of the US is routinely practiced during late fall (November) through spring (late March) each year (Horn et al, 1981; Pinchak et al, 1996; Min et al, 2005, 2006; Horn, 2006; Sij et al, 2007). The onset of bloat is variable between animals and depends on the rate of fermentation of wheat forage and production of ruminal gas, passage rate, and foaming properties of rumen contents (Cole and Boda, 1960; Bartley and Bassette, 1961). Frothy bloat increases the intraruminal pressure with abdominal distension, which interferes with nerve receptors at the reticulorumen juncture and as a result the eructation mechanism is impaired (Cole and Boda, 1960). These adverse effects disturb homeostasis in the rumen, reducing the production value of the animal. About 2–3% mortality is reported due to bloat, and is considered a serious threat to beef farmers (Horn, 2006)
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