Ruminants - Fermentation - Carbohydrates

11 important questions on Ruminants - Fermentation - Carbohydrates

How are carbohydrates fermented in the rumen?

Cellulase enzymes on bacterial surfaces hydrolyze cellulose, hemicellulose and pectin into monosaccharides (glucose, galactose, fructose)

How are carbohydrates absorbed?

Monosaccharids are absorbed by bacteria, and the waste products of glucose fermentation become VFAs that are absorbed by ruminants and used for energy

How is each monosaccharide broken down in the rumen?

Each monosaccharide becomes two pyruvate molecules, NADH, H+, ATP, and CO2
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What are the different types of volatile fatty acids?

Methanogens (Acetate, methane), butyrate, propionate, lactate (undergoes further digestion to acetate and propionate)

How is lactate further broken down in the rumen?

3 lactate molecules lead to 2 propionates, 1 acetate and 1 methane, or ATP, CO2, H2O

What are the main VFAs absorbed by the ruminants?

Acetate, propionate, butyrate

Where are VFAs absorbed in ruminants?

Reticulum, rumen, and omasum, across stratified squamous epithelium by diffusion down concentration gradients

What is the purpose of absorbing VFAs?

Prevents rumen acidosis and supplies energy

What is the most abundant VFA in ruminant feed?

Acetate (60-70%), then propionate (20-30%), then butyrate (10%)

What is the ideal rumen pH to absorb VFAs?

At normal rumen pH (5.5–6.8), VFAs are mostly ionized (negatively charged) and therefore poorly absorbed. The apical surface has a lower pH (due to Na⁺/H⁺ exchange), which converts VFAs into their non-ionized (HVFA) form, allowing easy absorption. Lactate, with a lower pKa (~3.9), remains ionized even at this lower pH and is therefore poorly absorbed.

What are each VFA used for in the ruminant?

Acetate: Energy/lipid production by various tissues
Propionate: Gluconeogenesis by the liver
Butyrate: Metabolized into a ketone inside rumen epithelial cells

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