Definition

Microbial protein is formed in the rumen when microbes utilise fermentable organic matter from the ration. This protein typically represents the largest share of intestinal digestible protein and provides an amino acid profile that closely matches the requirements for milk protein synthesis. 

Importance

Microbial protein is a key component of the Intestinal digestible protein system because:

• It supports milk production through a balanced amino acid pattern.
• It is largely dependent on rumen fermentation processes and energy availability.

Evolution of the Intestinal digestible protein system

Old system (1991):

Microbial protein production was assumed constant at 150 g per kg of fermentable organic matter.

Current system (2007):

• Considers the actual amount of Rumen Fermentable Organic Matter (RFOM).
• Accounts for energy released during rumen breakdown, which varies by carbohydrate fraction.
• Includes efficiency factors for how microbes use available energy and protein, influenced by whether nutrients are dissolved in rumen fluid or present as coarse particles.

Key factors affecting microbial protein production

• Balance of fermentable carbohydrates
• Energy availability during rumen fermentation
• Physical form of feed particles
• Microbial efficiency in converting energy and protein

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