Question

Describe, compare and contrast hindgut and foregut fermentation. Include a description of the digestive tract morphology, representative taxa, and advantages and disadvantages for each type of digestion. include significant discussion on the symbiotic relationship between herbivores and microbes (e.g., bacteria) and should contain a minimum of 400 words.

Answer 1

​​​​ANSWER :-

Point 1 :- Basically, the gastrointestinal system is composed of the forget, midgut and the hindgut. In case of ruminant animals like the cattles, there are three additional chambers that are not specific for absorption of any nourishment but are specific for having a symbiotic association with certain microbial colonies that aid in fermentation. Basically, these ruminants feed on plants which have a high cellulose content in their cell wall which cannot be directly broken down in the presence of their own digestive enzymes which do not include cellulase. Certain microbes are able to produce cellulase which resides in the ruminant foregut region prior to the stomach. These facilitate digestion of the plant cell wall content and makes available volatile fatty acids after the fermentation is carried out. These adds up to the fuel producing substrate of the animal. In case of non-ruminant animals like the rabbits, there is chamber specific to aid in microbial digestion present post stomach.

Point 2 :- The foregut in case of the ruminants is provided with three chambers namely the rumen, reticulum, omasum and the abomasum out of which maximum fermentation rate can be seen in case of the rumen which is the largest compartment. The cells of the three chambers are provided with squamous epithelia cells which supports the microbial colonies. There are tiny projections arising from every compartment which enhances the surface area for encompassment of the bacterial colonies. In case of the non-ruminants, the fermentation is carried out mainly in the caecum and the colon which is a part of the hindgut. At the same time, it should be specified that the absorption of the nutrients along with fermentation can happen in the colon part of the large intestine.

Point 3 :- Advantage to the ruminants is that due to enhanced microbial digestion, there is relatively less mastication needed in order to metabolize the components. Much of the volatile fatty acids gets easily absorbed as they reach the intestine. Advantage to the non-ruminant is that there is better digestion of Carbohydrates as compared to the ruminants as they depend mainly upon mastication in order to breakdown the components. Although, there is no other advantage in terms of cellulose digestion and absorption as seen in the ruminants.

Point 4 :- Disadvantage of having a foregut fermentation process is that once there is intake of food there is a limit to which the food is being fermented. It means that it takes longer durations to completely ferment the substrates and thus they can consume only a limited amount of food. In case of hindgut fermentation, as the microbial fermentations occurs in the hindgut region, absorption of the cellulose derived components is very less as it is lost through the body in the form of fecal matter.

The ruminants include the even-toed ungulates (Artiodactyl) such as cows and the non-ruminants include the odd-toed ungulates such as zebras (Perissodactyl)

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