lecture 9 - starch fermentation and VFA production

How is starch broken down by rumen microbes?

Extracellular enzymes break it into smaller sugars

Name three major starch-fermenting bacteria.

Prevotella ruminicola, Ruminobacter amylophilus, and Streptococcus bovis

Can starch-fermenting bacteria use ammonia?

Yes, but they may prefer amino acids and peptides

What is proteolysis?

Protein breakdown into smaller peptides and amino acids

What do peptides and amino acids provide to microbes?

Nitrogen and building blocks for growth

What are the three major rumen VFAs?

Acetate, propionate, and butyrate

What is the typical acetate molar proportion?

About 55–75%

What is the typical propionate molar proportion?

About 15–30%

What is the typical butyrate molar proportion?

About 5–15%

How do you calculate VFA molar proportion?

Individual VFA moles ÷ total VFA moles × 100%

What is VFA concentration?

The amount of VFA per volume, commonly measured in mM

How does concentration differ from molar proportion?

Concentration is amount per volume; molar proportion is the percentage of total VFAs

What do all VFA molar proportions add up to?

100%

Which VFA proportion generally increases on high-fiber diets?

Acetate

Which VFA proportion generally increases on high-starch diets?

Propionate

Which carbohydrate has the highest VFA production rate in the lecture comparison?

Starch

Which feeds are generally high in structural fiber?

Forages

Which feeds are generally high in starch and sugars?

Concentrates

What can succinate and lactate be converted into?

Both can be converted to propionate

What happens to VFA production when rapidly fermentable starch is abundant?

VFA production can increase quickly

Why can diets high in rapidly fermentable carbohydrates lower rumen pH?

They can produce VFAs faster than they are absorbed

What is the difference between acetate and propionate in hydrogen balance?

Acetate production generates hydrogen; propionate production uses hydrogen