Section 5: Ruminal Fermentation Products: VFA and Methane

What are the 3 major VFAs?

Acetate

Butyrate

Propionate

How many carbons are in acetate?

2

How many carbons are in butyrate?

4

How many carbons are in propionate?

3

How many carbons are in valeric acid?

5

What is the pKa of VFAs?

<4.8

As digestibility of diet increases what happens to concentration of VFAs?

It goes up

What is the acetate : propionate in a forage diet?

3-5:1

What is the acetate : propionate in a grain diet?

1.5-2:1

Formic, acetic, propionic, butyric, and valeric are all products of what fermentation?

Products of carbohydrate, protein, and lipid fermentation

Isobutyric, isovaleric, and 2-methylbutyric are all products of what fermentation?

Amino acid fermentation because they are branched chain

What has to happen in order for proteins to become VFAs?

They need to be deaminated

What VFA does proline become?

Valerate

What VFA do carbohydrates become?

Valerate

What VFA does valine become?

Isobutyric

What VFA does leucine become?

Isovaleric

What VFA does isoleucine become?

2-methylbutyric acid

What two types of reactions occur to create branched VFAs from amino aicds?

Deamination

Decarboxylation

What 5 VFAs are mostly metabolized by microbes in the rumen?

Formic

Valeric

Isobutyric

Isovaleric

2-methybutyric

What % of produced VFAs are absorbed in the rumen?

80%

What % of produced VFAs are absorbed in the omasum?

15%

What % of produced VFAs are absorbed in the abomasum?

5%

What are the 2 locations for metabolism of VFAs?

Gut epithelium and liver

Rank butyrate, acetate, and propionate on how fast they will be absorbed via passive diffusion?

Butyrate

Propionate

Acetate

What kind of relationship does pH and absorption of VFAs have?

Inverse (pH decreases absorption increases)

What is SARA?

Subacute ruminal acidosis

• high VFA concentration but not high enough to cause major clinical signs. Economic problem, does get diagnosed often

What are the clinical signs of SARA?

Decreased fat content in milk

Reduction of eating

Decreased ruminal contractions

Pasty or soupy feces

Decreased milk productions

laminitis

How can you prevent SARA?

increase forage content and buffers

What is the metabolism of VFAs in the epithelium by %?

Butyric: 80%

Propionic: 20-50%

Acetic: <5%

T/F lactic acid is gluconeogenic?

True

What is formic acid converted into?

Methane

What VFAs are minimally absorbed and mostly metabolized by the microbes?

Formic, isobutyric, isovaleric, 2-methybutyic, and valeric acid

What are important growth factors for fiber-digesting bacteria?

Br-Chain VFAs

What is the application of using Br-Chain VFAs as growth factors of fiber-digesting bacteria?

You can supplement the feed with proteins like soybean meal or alfalfa to offset the lower fiber quality grass in the winter

What are the 5 ways VFAs can be used by ruminants?

1. Krebs cycle (ATP production)

2. Ketone body production

3. Create long chain fatty acids

4. Glucose production

5. Amino acid synthesis

What is the only VFA that is gluconeogenic?

Propionate

How much ATP can be made from acetate?

10

How much ATP can be made form propionate?

18

How much ATP can be made from butyrate?

26

What are the 2 ketogenic VFAs and which one is used more?

Acetate and butyrate

Butyrate is used more

What are the two lipogenic VFAs and what is the main one?

Acetate and butyrate

Acetate is main lipogenic

What is the only amino genic VFA?

Propionate

How is acetate used to make ATP?

It is turned into acetyl-CoA then citrate and enters the citric acid cycle

How does propionate enter the citric acid cycle?

Propionate TO Propionyl CoA TO Succinyl CoA

T/F acetate can become pyruvate?

False

T/F propionate can become pyruvate?

True

What are the 3 main ketone bodies?

Acetone

Acetoacetate

Beta-hydroxybutyrate

How are ketone bodies produced in monogastrics?

Via oxidation of LCFAs in the liver

How are ketone bodies produced in ruminants?

From butyrate in ruminal epithelial cells

What is ketosis?

Accumulation of ketone bodies in the blood

What animal group is most susceptible to ketosis?

High-producing dairy cows in early lactation

What is the cause of ketosis?

There is a negative energy balance and the cow needs to meet glucose demands for milk production so fatty acids are oxidized creating ketone bodies

What VFA is not present enough when ketosis happens?

Propionic acid

How can you treat ketosis?

Oral dosing of propionic acid or propylene glycol, IV glucose

Rank acetic, propionic, and butyric based on how efficient their energy production is

Propionic (109%)

Butyric (77.9)

Acetic (62)

What are the 3 main reasons why propionic acid is so important?

Reduce methane production

More energy than acetate

Only gluconeogenic fatty acid

What type of diet will lead to an increase in propionic acid?

High grain

• Lower ruminal pH promotes propionic acid

• Starch-fermenters produce propionic acid

What type of antibiotic can be added to feed to increase propionic acid production?

Ionophore antibiotics like monensin

T/F methane is a waster product?

True

How much energy is lost with methane production?

5% on grain based

15% on forage feed

What is the reason why so much methane is produced?

It allows the rumen to dispose of excess hydrogen

What are the 2 major ways to produce methane?

H2 and CO2

Formate acid

What are the 2 minor ways to produce methane?

Methanol

AMines

What are the 2 justifications for the inhibition of methane production?

Increase feed efficiency

Reduce global warming

How does methane affect global warming directly?

By producing CO2 during atmospheric oxidation

How can we inhibit methane production?

1. Reduce H2 production

2. Diversion of H2 to different electron sinks

3. Inhibition of reduction of methanogens

Can can fats be used to reduce methane production?

It you take the excess hydrogen in the rumen and create fats with it then there will be less emissions

What is the role of 3-nitrooxypropanol (NOP) in methane reduction?

It can block the reaction of CO2 and H2 that forms methane. Not approved in the USA

T/F NOP alters milk production?

False