Discuss the major sources and fate of the following substances in ruminant digestion.
_propionic, ethanoic and butanoic acid
_Methane
_Carbon dioxide
_Ammonia
Propionic, ethanoic, and butanoic acid are volatile fatty acids (VFAs) that are produced during ruminant digestion through the fermentation of carbohydrates by rumen microorganisms.
The major source of propionic, ethanoic, and butanoic acid is the breakdown of plant fibers, such as cellulose and hemicellulose, by cellulolytic bacteria in the rumen. These bacteria ferment the fibers into simpler compounds, including VFAs. The VFAs, particularly propionic acid, play a crucial role in providing energy to the ruminant as they are absorbed through the rumen wall and utilized by the animal.
Methane is another byproduct of rumen fermentation and is primarily produced by methanogenic archaea. These archaea break down the VFAs produced by cellulolytic bacteria, particularly acetate, to produce methane. Methane production occurs via a process called enteric fermentation, which takes place in the rumen of ruminant animals such as cattle, sheep, and goats. It is estimated that approximately 2-12% of the energy intake of ruminants is lost as methane gas. Methane is then released into the rumen and ultimately expelled by the animal through belching.
Carbon dioxide (CO2) is produced during ruminant digestion through various processes. Firstly, CO2 is a byproduct of the fermentation process carried out by rumen microorganisms to produce VFAs. Secondly, CO2 is also produced during the breakdown of carbohydrates that contain carbon, such as sugars and starches. Finally, ruminant animals also produce CO2 as a result of their own cellular respiration.
Ammonia (NH3) is produced as a byproduct of protein degradation in the rumen. When rumen microorganisms break down dietary proteins using proteolytic enzymes, ammonia is formed. This ammonia can be utilized by rumen microorganisms as a source of nitrogen for the synthesis of microbial protein. Some of the microbial protein is then digested by the host ruminant, providing essential amino acids for its growth and metabolism.
The fate of these substances in ruminant digestion varies. Propionic, ethanoic, and butanoic acids are absorbed across the rumen wall and are utilized as a source of energy by the ruminant. Methane, on the other hand, is primarily expelled through belching by the animal but can also be partially absorbed in the rumen and transported through the bloodstream to other tissues. Carbon dioxide is also expelled through belching, but it can also be absorbed across the rumen wall and utilized by the animal's metabolism.
Ammonia is partially used by rumen microorganisms for protein synthesis or can be absorbed across the rumen wall and utilized by the ruminant as a source of nitrogen for its own protein synthesis. However, excess ammonia can be toxic to the animal, and therefore, ruminants have efficient mechanisms to convert and excrete excess ammonia as urea in the urine. Urea can then be recycled in the rumen by rumen microorganisms to be converted into microbial protein.