Discuss the major source and fate of the following substances in ruminant digestion.
i. Propionic, ethanoic and butanoic acid
ii. Methane
iii. Carbon dioxide
iv. Ammonia
i. Propionic, ethanoic, and butanoic acid: These short-chain fatty acids are produced in the rumen during the fermentation of carbohydrates by rumen microorganisms. Carbohydrates are broken down into simpler compounds like glucose, which is then metabolized by bacteria to produce these fatty acids. These fatty acids are important energy sources for ruminants as they are absorbed through the rumen wall into the bloodstream.
ii. Methane: Methane gas is primarily produced in the rumen by methanogenic archaea. These microorganisms use hydrogen gas (H2) produced during carbohydrate fermentation and carbon dioxide (CO2) as substrates to produce methane (CH4). Methane is released by burping or eructation and contributes to the greenhouse gas emissions from ruminant agriculture.
iii. Carbon dioxide: Carbon dioxide is produced in the rumen through various processes. It is a byproduct of rumen fermentation, where carbohydrates are broken down into volatile fatty acids. It is also generated during the metabolism of various substrates by rumen microorganisms. Carbon dioxide is released to the atmosphere by eructation or dissolved in the rumen fluid and absorbed through the rumen wall.
iv. Ammonia: Ammonia is formed in the rumen through the breakdown of dietary proteins by rumen microorganisms. Proteins are broken down into amino acids, and these amino acids are further degraded to produce ammonia. The ammonia is then used by rumen microorganisms to synthesize microbial protein, which is a crucial nutrient for ruminants. Some ammonia is also absorbed through the rumen wall and enters the bloodstream for utilization by the animal or processed by the liver into urea for nitrogen recycling.