Abstract
The chemical composition of barley grain can vary among barley varieties (Fibar, Xena, McGwire, and Hilose) and result in different digestion efficiencies in the rumen. It is not known if compositional differences in barley can affect the microbiota involved in the ruminal digestion of barley. The objective of this study was to characterize the in situ rumen degradability and microbiota of four barley grain varieties and to compare these to corn. Three ruminally cannulated heifers were fed a low (60% barley silage, 37% barley grain, and 3% supplement) or high grain (37% barley silage, 60% barley grain, and 3% supplement) diet. One set of bags was used to estimate dry matter (DM), starch and crude protein (CP) degradability. A second set was used to extract DNA from the adherent microbiota and visualize grain after incubation using scanning electron microscopy (SEM). DNA was subjected to amplicon 16S rRNA gene sequencing followed by analysis using QIIME. In the low grain diet, McGwire had the highest effective degradability (ED) of DM (P < 0.01). The ED of starch was highest (P < 0.01) for Fibar, McGwire, and Xena, but the ED of CP was not affected by variety. For the high grain diet, Xena and McGwire had the highest ED of DM (P < 0.01). The ED of starch was highest (P < 0.01) for Xena and Fibar. The ED of protein was highest (P < 0.01) for Xena and McGwire. Although the microbiota did not differ among barley varieties, they did differ from corn and with incubation time. Lactobacilli were dominant members of the mature biofilms associated with corn and barley and were accompanied by a notable increase in the lactic acid utilizing genera, Megasphaera. As none of the cattle exhibited subclinical or clinical acidosis during the study, our results suggest that lactobacilli play a more prominent role in routine starch digestion than presently surmised.
Highlights
Barley is ranked as the fourth major cereal crop in the world consumed by humans and livestock (Nikkhah, 2012) and is the primary grain fed to ruminants in Western Canada (Nikkhah, 2012)
Previous studies of the microbiota involved in the ruminal digestion of barley grain have primarily relied on culture-based methods and were limited to only those bacteria that could be grown in the laboratory
Corn was included in the study as a positive control as it is well known that the chemical composition of corn differs dramatically from barley (Peter and Herbert, 2013) and grain colonization was investigated using heifers fed both low and high grain diets
Summary
Barley is ranked as the fourth major cereal crop in the world consumed by humans and livestock (Nikkhah, 2012) and is the primary grain fed to ruminants in Western Canada (Nikkhah, 2012). Little is known about how differences in barley grain composition affect the types of rumen bacteria that form biofilms on the surface of barley grain. NGS is a culture-free method that enables analysis of the entire bacterial population based on sequencing of the16S rRNA gene It enables the characterization of the phylogeny and taxonomy of bacteria including those that are associated with complex biofilms. We hypothesized that the population structure of rumen microbial biofilms would differ among barley varieties as a result of differences in their chemical composition. Corn was included in the study as a positive control as it is well known that the chemical composition of corn differs dramatically from barley (Peter and Herbert, 2013) and grain colonization was investigated using heifers fed both low and high grain diets
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