discuss the major sources and fate of the following substances in ruminant digestion.

Question

1 propionic, ethanoic and butanoic acid
2 methane
3 carbon dioxide
4 ammonia

Answer 1

1. Propionic, ethanoic, and butanoic acid: These substances are produced during the microbial fermentation of carbohydrates in the rumen of ruminant animals. Carbohydrates such as starch and cellulose are broken down by rumen microbes into volatile fatty acids (VFAs), with propionic, ethanoic, and butanoic acid being the major VFAs produced. These VFAs serve as an energy source for ruminants.

As for their fate, a significant portion of the VFAs, including propionic, ethanoic, and butanoic acid, are absorbed through the rumen wall and transported to the liver through the bloodstream. In the liver, these VFAs are further metabolized into glucose and other important metabolic intermediates. Glucose is then utilized by the ruminant as the main source of energy for various physiological processes.

2. Methane: Methane is a byproduct of the microbial fermentation of feed components in the rumen, primarily through the action of methanogenic archaea. It is indeed the major greenhouse gas emitted by ruminant animals. Methane production in ruminants occurs mainly during the anaerobic breakdown of fibrous carbohydrates, such as cellulose and hemicellulose.

The fate of methane is that a significant proportion is eructated or belched out by the ruminants. Once released into the atmosphere, methane contributes to global warming due to its high heat-trapping potential. It is estimated that livestock, including ruminants, contribute around 14.5% of global methane emissions.

3. Carbon dioxide: Carbon dioxide (CO2) is a byproduct of ruminal fermentation, primarily arising from microbial metabolism of feed carbohydrates. Although methane is often considered the primary gas of interest when discussing greenhouse gas emissions from ruminants, CO2 is also emitted, although in lower quantities.

The fate of carbon dioxide released during ruminant digestion is diverse. Some CO2 dissolved in the rumen fluid can be absorbed and utilized by rumen microorganisms in their metabolic processes. Furthermore, a small proportion is absorbed from the rumen and transported through the bloodstream to various tissues. Ultimately, CO2 is released from the animal's respiratory system during exhalation.

4. Ammonia: Ammonia (NH3) is formed in the rumen as a result of microbial degradation of dietary proteins and subsequent deamination of amino acids by rumen bacteria. Ammonia is primarily produced from the breakdown of urea, which is present as a waste product in the animal's urine and is reabsorbed into the rumen.

Regarding its fate, a significant proportion of ammonia in the rumen is utilized by rumen microorganisms in their own growth and synthesis of microbial protein. Some ammonia is also absorbed through the rumen wall and transported to the liver where it is converted into urea to be re-excreted through the urine. Additionally, a portion of the ammonia is used by the ruminant to meet its nutritional requirements for protein synthesis.