Abstract
The success of nutritional strategies for the prevention of subacute ruminal acidosis (SARA) and the related microbial dysbiosis still remains unpredictable due to the complexity of the rumen ecosystem. The rumen epimural community, due to proximity, has the greatest opportunity to influence host gene expression. The aim of this study was to determine the effect of two separate feed additives on the rumen epimural community and host epithelial gene expression. Eight rumen cannulated Holstein cows were randomly assigned to one of three feeding groups: autolyzed yeast (AY), phytogenics (PHY) and control (CON) using a 3 × 3 Latin square design. Cows were fed an intermittent SARA model that started with 100% forage diet (Baseline) followed by two 65% concentrate-diet induced SARA challenges (SARAI, SARAII), separated by 1 week of forage only feeding. Rumen papillae samples were collected via the cannula during the Baseline, SARAI and SARAII periods. Microbial DNA was extracted and sequenced targeting the 16S rRNA gene and host RNA was analyzed using RT-qPCR. Analysis of the taxonomic composition at the genera level showed a tendency to increase in the relative abundances of Pseudobutyrivibrio (P = 0.06), Selenomonas (P = 0.07) and significantly increase in SHD-231 (P = 0.01) in PHY treated animals, whereas Succiniclasticum tended to decrease in both PHY and AY treated animals compared to the control. Linear discriminant analysis effect size testing was performed and based on treatment × feeding phase interaction, a number of biomarker genera were identified including the previously identified Succiniclasticum. Supplementation with AY correlated positively with CD14 and DRA expression and negatively to CLDN1, MyD88, and MCT4 expression. Supplementation with PHY showed a negative correlation to CLDN4 gene expression. Anaerovibrio showed the highest positive Pearson correlations to biogenic amines tested in the rumen fluid including putrescine (r = 0.67), cadaverine (r = 0.84), and tyramine (r = 0.83). These results show that supplementing feed additives to high grain diets can have a positive influence on the stability of the epimural populations, and that changes in the epimural community are correlated with changes in host epithelial gene expression.
Highlights
The rumen is a complex microbial ecosystem in the foregut of ruminants, which is evolutionarily adapted to a fiber-rich diet, allowing them to utilize complex carbohydrate sources not suitable for human-nutrition
The aim of this study was to determine the effect of supplementation of PHY or AY feed additives under repeated bouts of diet induced subacute ruminal acidosis (SARA) on rumen epithelial microbial populations, and host papillae gene expression, as well as their interaction with regards to barrier function, and proinflammatory signaling
Gramnegative bacteria are the source of the rumen endotoxin, a pro-inflammatory molecule that has been attributed to several symptoms of SARA, and is known to increase in luminal concentration under high-grain feeding (Plaizier et al, 2012)
Summary
The rumen is a complex microbial ecosystem in the foregut of ruminants, which is evolutionarily adapted to a fiber-rich diet, allowing them to utilize complex carbohydrate sources not suitable for human-nutrition. The modern production practice of feeding large amounts of concentrate for increased physiological energy requirements can disrupt this ecosystem resulting in microbial dysbiosis This dysbiosis is commonly described as subacute ruminal acidosis (SARA), defined as extended periods of time (>5 h/day) where ruminal pH is below physiological range (5.8; Zebeli et al, 2008). The use of bioactive phytochemicals as natural feed additives has recently gained interest as an antibiotic alternative for modifying rumen fermentation favorably, such as by minimizing rumen methanogenesis and improving rumen fermentation (Flachowsky and Lebzien, 2012) Prebiotics such as autolyzed yeast have been used to increase fiber and starch digestion (Harrison et al, 1988; Mao et al, 2013), to prevent rumen acidosis (Nocek et al, 2011; Ganner and Schatzmayr, 2012), and to accelerate rumen microbial biofilm development (Chaucheyras-Durand and Fonty, 2002). The effectiveness of these nutritional interventions is highly variable depending upon the interactions among the chemical structure of the supplement, the diet, and the adaptability of the rumen microbiota
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