A Metagenomics Approach to Evaluate the Impact of Dietary Supplementation with Ascophyllum nodosum or Laminaria digitata on Rumen Function in Rusitec Fermenters

Abstract

There is an increasing need to identify alternative feeds for livestock that do not compete with foods for humans. Seaweed might provide such a resource, but there is limited information available on its value as an animal feed. Here we use a multi-omics approach to investigate the value of two brown seaweeds, Ascophyllum nodosum (ASC) and Laminaria digitata (LAM), as alternative feeds for ruminants. These seaweeds were supplemented at 5% inclusion rate into a control diet (CON) in a rumen simulation fermenter. The seaweeds had no substantial effect on rumen fermentation, feed degradability or methane emissions. Concentrations of total bacteria, anaerobic fungi, biodiversity indices and abundances of the main bacterial and methanogen genera were also unaffected. However, species-specific effects of brown seaweed on the rumen function were noted: ASC promoted a substantial decrease in N degradability (-24%) due to its high phlorotannins content. Canonical correspondence analysis of the bacterial community revealed that low N availability led to a change in the structure of the bacterial community. ASC also decreased the concentration of Escherichia coli O157:H7 post-inoculation. In contrast, LAM which has a much lower phlorotannin content did not cause detrimental effects on N degradability nor modified the structure of the bacterial community in comparison to CON. This adaptation of the microbial community to LAM diets led to a greater microbial ability to digest xylan (+70%) and carboxy-methyl-cellulose (+41%). These differences among brown seaweeds resulted in greater microbial protein synthesis (+15%) and non-ammonia N flow (+11%) in LAM than in ASC diets and thus should led to a greater amino acid supply to the intestine of the animal. In conclusion, it was demonstrated that incorporation of brown seaweed into the diet can be considered as a suitable nutritional strategy for ruminants; however, special care must be taken with those seaweeds with high phlorotannin concentrations to prevent detrimental effects on N metabolism. This study highlights the value of combining fermentation and enzyme activity data with molecular characterization of the rumen microbiome in evaluating novel feeds for ruminants. Further experiments are required to determine the maximum seaweed inclusion rate tolerated by rumen microbes.

Keywords: Ascophyllum nodosum; Laminaria digitata; Rusitec; brown seaweed; phlorotannins; rumen microbiome.

Figure 1

Effect of 5% supplementation of a Control diet (CON) with Ascophyllum nodosum (ASC) or Laminaria digitata (LAM) on pH (A), lactate concentration (B), amylase activity (C), xylanase activity (D), carboxymethyl-cellulase activity (E), and Escherichia coli concentrations (F) post-inoculation in the rumen simulating fermenter Rusitec. Error bars indicate the standard error of the difference for each time point (n = 4). ^**P < 0.01, ^*P < 0.05, ^†P < 0.1.

Figure 2

(A) Canonical correspondence analysis illustrating the relationship between the structure of the bacterial community and the rumen fermentation pattern in the rumen simulating fermenter Rusitec. Arrows show the direction of the gradient and those longer that the dotted circle are significant (P < 0.05). Centroid is indicated for each treatment: Control (CON), Ascophyllum nodosum (ASC) and Laminaria digitata (LAM). Animals used as donors are indicated in numbers. (B) Heat map describing the effect of the diet on the structure of the bacterial comunity and on the abundance of the main genera. Dendrogram is based on the UPGMA clustering of the Bray-Curtis distances. The total number of reads per sample was log transformed and minor genera discarded (<0.1%).

Figure 3

(A) Canonical correspondence analysis illustrating the relationship between the structure of the methanogen community and the rumen fermentation pattern in the rumen simulating fermenter Rusitec. Arrows show the direction of the gradient and those longer that the dotted circle are significant (P < 0.05). Centroid is indicated for each treatment: Control (CON), Ascophyllum nodosum (ASC), and Laminaria digitata (LAM). Animals used as donors are indicated in numbers. (B) Heat map describing the effect of the diet on the structure of the methanogen community and on the abundance of the main methanogen species. Dendrogram is based on the UPGMA clustering of the Bray-Curtis distances. The total number of reads per sample was log transformed and minor genera were discarded (<0.1%).

Figure 4

Effect of 5% supplementation of a Control diet (CON) with Ascophyllum nodosum (ASC) or Laminaria digitata (LAM) on abundance of the main bacteria (A–C) and methanogen (D) phyla and families in the rumen simulating fermenter Rusitec.