Discuss the major source and fate of the following substance in ruminant digestion
I. Propionic, ethanoic and butanoic acid
ii. Methane
iii. Carbon dioxide
iv. Amonia
I. Propionic, ethanoic, and butanoic acid:
The major source of propionic, ethanoic, and butanoic acid in ruminant digestion is the fermentation of carbohydrates by the microbial population present in the rumen. Carbohydrates, such as starches and sugars, are broken down into simpler compounds like glucose and then further fermented by the rumen microbiota. This fermentation process leads to the production of volatile fatty acids (VFAs), including propionic acid, ethanoic acid (acetic acid), and butanoic acid (butyric acid). These VFAs are absorbed by the rumen wall and serve as a significant source of energy for the ruminant.
The fate of these VFAs varies. Propionic acid is primarily used as an energy source by the ruminant, as it can be transformed into glucose in the liver through gluconeogenesis. It is an essential precursor for glucose synthesis. Ethanoic acid is also used as an energy source by the ruminant, though to a lesser extent. Butanoic acid, on the other hand, is primarily utilized by the rumen epithelium itself as an energy source. The concentration of these VFAs can be influenced by the type and amount of feed provided to the ruminant.
II. Methane:
The major source of methane (CH4) in ruminant digestion is the anaerobic fermentation of feed by methanogenic archaea present in the rumen. These methanogens produce methane as a byproduct during the breakdown of complex polysaccharides like cellulose and hemicellulose. Methane production is an inevitable result of the microbial fermentation occurring in the rumen.
Methane has a relatively low solubility in rumen fluid and readily escapes into the atmosphere. The majority of the methane produced by ruminants is eructated (released through belching) and escapes through the mouth. A small fraction of methane can also be absorbed and excreted via the lungs. Once released into the atmosphere, methane is a potent greenhouse gas and contributes to global warming.
III. Carbon dioxide:
Carbon dioxide (CO2) in ruminant digestion has multiple sources. The primary source of CO2 is the fermentation of carbohydrates and fiber by rumen microbes, similar to the production of VFAs. Additionally, some CO2 is produced during the metabolism of VFAs in the rumen epithelium and in other tissues of the ruminant.
The fate of carbon dioxide varies. Some CO2 is eructated along with methane and expelled through belching. CO2 can also be absorbed across the rumen wall and enter the bloodstream. Once in the bloodstream, CO2 can be transported to the lungs and exhaled.
IV. Ammonia:
Ammonia (NH3) is mainly produced in the rumen by the deamination or breakdown of dietary protein by rumen microorganisms. This deamination process releases ammonia in the rumen fluid. Ammonia can also be formed through the hydrolysis of urea, which is a nitrogenous compound in the saliva of ruminants.
The fate of ammonia depends on various factors including its concentration, rumen pH, and diet composition. Some of the ammonia is utilized by rumen microorganisms, which convert it into microbial protein. This microbial protein is then further digested and utilized by the ruminant as a source of protein. A portion of the ammonia is absorbed across the rumen wall and enters the bloodstream. It is then transported to the liver, where it is primarily converted into urea and subsequently excreted in the urine.