What is the difference between foregut and hindgut fermentation

The higher representation of Bacteriodetes and Spirochaetes in the foregut may be related to higher cellulolytic activity, whereas hindgut dominance by Proteobacteria and Firmicutes might be related to higher proteolytic activity Appleby, ; Mackie and Wilkins, That the cow rumen was richer than the hoatzin crop is likely linked to habitat size, in direct relation with richness Chesson, , as predicted by the theory of island biogeography MacArthur and Wilson, A higher relative abundance of Spirochaetes, Verrucomicrobia and Lentisphaerae in the cow rumen is consistent with high cellobiose degradation Zoetendal et al.

Indeed, the rumen has been shown to be more efficient in degrading cellulose than the hoatzin crop Jones et al. Diet is surely a major determinant in shaping digestive communities Tajima et al. The hoatzin is a browser, consuming green leaves, bark and green stems from young plants, low in fiber and high in nitrogenous compounds, whereas the cow is a grazer that feeds on grasses monocots.

There are major chemical differences between monocot and dicot cell walls. Legumes and most dicots contain smaller proportions of hemicellulose in their cell walls than monocots Van Soest, whereas these have extensive interconnecting networks of phenylpropanoids Iiyama et al. This comparative work shows that the similarity in the microbial composition between these evolutionarily distant hosts is a case of evolutionary convergence.

Despite the considerable phylogenetic divergence between the hosts and dietary differences there are strong similarities in the foregut and hindgut communities of hoatzins and cows. We conclude that host characteristics that is, phylogeny, diet, size and weight are less important than the functional niche of the organ for differentiating bacterial community composition.

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Raskin , L. Hindgut fermenters have a shorter passage time than ruminants, and hence are less efficient in cellulose digestion, for which they compensate with a higher intake of food Clauss et al.

Note that an additional problem for hindgut fermenters is that they must access the cell contents of the herbage prior to the fermentation of the cellulose in the hindgut. Although the products of cellulose fermentation can be absorbed in the colon, the enzyme-producing glands for the digestion of the sugars, fats and proteins of the cell contents are located in the small intestine.

Some non-ungulate hindgut fermenters, such as rabbits and certain rodents, circumvent this problem by refection eating the initially-produced faeces : however, refection is not practiced by any ungulate nor by hyraxes and elephants. Thus it must be the case, for hindgut fermenting ungulates, that the initial mastication of the food is sufficient to fracture the plant cell walls to release the cell contents prior to the site of cellulose fermentation Janis et al.

Thus, hindgut fermenters face two functional problems with food comminution in which they differ from ruminants. Not only must they consume more food per day than a ruminant of similar size and diet, but they must also ensure that the cell walls are ruptured on initial food ingestion while a ruminant can rely on fermentation to break down the cell walls. One would therefore predict that initial food mastication would be more prolonged and intensive in hindgut fermenters than in ruminants.

Even though ruminants later regurgitate their food and chew it as cud, at this point the food has been softened by fermentation processes and may present a reduced load on the masticatory system Fortelius Morphological studies do appear to show that hindgut fermenters have deeper jaws, larger areas for the insertion of masticatory muscles and greater cheek tooth occlusal area than ruminants e. However, these observations have not been subjected to rigorous biomechanical analysis.

Both animals have been the subject of many agricultural studies, and while other ruminants have also been studied in this fashion sheep, deer, llamas, etc.