VFA and Protein Metabolism

Question 1

VFA metabolism

Answer 1

-blood from the rumen enters the portal vein and takes VFAs to the liver
>metabolism of VFAs (acetate, propionate, butyrate) occurs

Question 2

Acetate metabolism in liver

Answer 2

-acetate to acetyl-CoA occurs
>acetate enters the TCA cycle producing ATP
>Fatty acid synthesis occurs

Question 3

Propionate metabolism in liver

Answer 3

-used in gluconeogenesis
>propionate to oxaloacetate to 4C glucose
ONLY VFA THAT CAN FORM GLUCOSE

Question 4

Butyrate metabolism in liver

Answer 4

-butyrate forms beta-hydroxybutyrate (ketone body)
-energy source for most tissues
-FA synthesis for milk fat

Question 5

VFA distribution to liver vs. rumen

Answer 5

-Acetate: 70% in rumen and only 50% of that to liver
-Propionate: 20% in rumen, only 10% of that to liver
-Butyrate: 10% in rumen, only 1% of that to liver

Question 6

What form do VFAs enter the peripheral body?

Answer 6

-Acetate enters as acetate
-Propionate enters as glucose
-Butyrate enters as beta-hydroxybutyrate

Question 7

Gluconeogenesis

Answer 7

-Oxaloacetate is required for gluconeogenesis and is made by the TCA cycle
>propionate is needed to form the oxaloacetate (therefore gluconeogenic precursors cannot become glucose)

Question 8

Insufficient feed intake (starch) impact

Answer 8

-low blood glucose
-not enough propionate for gluconeogenesis
-hypoglycemia
-ketosis

Question 9

Where does ruminant energy come from?

Answer 9

-produced mainly by VFAs (20-80%)
>glucose production from propionate
>TCA cycle from acetate and butyrate

Question 10

Hindgut fermenters (eg. Horses and neonate ruminants) and VFA metabolism

Answer 10

-any digestible carbohydrates already absorbed by animal in small intestines
>glucose absorbed from diet so less reliant on gluconeogenesis
-less substrate available for fermentation therefore VFAs less important as energy source

Question 11

Non-structural carbohydrates (sugars, starch, pectin) energy for animal

Answer 11

-little direct absorption by animal. These products are instead fermented by microbes to VFAs.
>Less VFAs reach the small intestine therefore VFAs yield less energy than if animal is able to directly absorb so less efficient than monogastrics.

Question 12

Structural carbohydrates (cellulose and hemicellulose)

Answer 12

-microbial digestion to monosaccharides, and these monosaccharides can be fermented to VFAs
-energy is not available to animal without microbial breakdown

Question 13

Protein and nitrogen metabolism

Answer 13

-Rumen degradable protein (RDP)- can be degraded in rumen by microbes
>becomes ammonia, peptides, and amino acids. All become microbial protein and then go to abomasum and small intestines
-Rumen undegradable protein (RUP)-cannot be fermented by microbes in rumen
>will pass directly to abomasum and small intestines
-bacterial N metabolism
-ammonia and N recycling
-balancing carbohydrates and nitrogen

Question 14

Common nitrogen sources

Answer 14

-True proteins (60-80%)- from diet/plants
-Nuclear proteins (10%)- proteins within nucleus of cells or bacteria
-non-protein nitrogen (5-30%)- anything nitrogenous entering the mouth or through metabolism which can be used by microbes
>ammonia and ammonium salts
>urea
>amides
>amines
>uric acid

Question 15

Rumen degradable protein (RDP)

Answer 15

-portion of protein degraded by rumen microbes
>only half of total crude protein, the other half is undegradable so known as bypass protein

Question 16

Bacterias role in rumen degradable protein

Answer 16

-only 10-40% of species will degrade protein
-extracellular proteases (protein to small peptides)
-small peptide absorbed (degraded to AA within the bacterial cell)

Question 17

Protozoas roles use of rumen degradable protein

Answer 17

-can utilize dietary protein
-generally consume bacteria for protein instead

Question 18

Rumen undegradable protein (RUP)

Answer 18

-dietary protein not digested by microbes=bypass protein
-digested by animal in small intestines

Question 19

Sources of rumen undegradable protein

Answer 19

-natural proteins (dehydrated alfalfa, feather meal, blood meal)
-Processed proteins (treated to protect from microbes)
>heat treatment (soybean meal), fat encapsulation (rumen protected methionine), formaldehyde denaturation, mineral chelation

Question 20

Bacterial nitrogen metabolism

Answer 20

1. bacteria deaminate amino acids into ammonia and carbon skeleton. This carbon skeleton can then be used for their own energy.
2. amino acids made into microbial protein
3. synthesize amino acids from ammonia and carbon skeleton

Question 21

Bacterial AA synthesis

Answer 21

-from ammonia and carbon skeleton=AA
-requires energy (important to balance carbohydrates and nitrogen supply during fermentation)

Question 22

Transamination by bacteria

Answer 22

-transfer amino group from one carbon skeleton to another
-can convert non-essential AA to essential AA = high quality microbial protein

Question 23

Ammonia sources

Answer 23

1.non-protein N from feed
2.Urea recycling

Question 24

Non-protein Nitrogen from feed

Answer 24

-nitrates/nitrites
-urea
-ammoniated straw

Question 25

Urea recycling from animal

Answer 25

-diffuses from blood into rumen
>urease enzyme in rumen epithelium converts urea to ammonia (results in concentration gradient that always promotes diffusion of urea into rumen)
-secreted in saliva which is then swallowed and re-enters rumen

Question 26

Ammonia absorption

Answer 26

1.excess ammonia in rumen is absorbed (NH3 absorbed rapidly, NH4 is not)
2.converted to urea by the liver
>energy cost
>blood urea nitrogen (BUN)
3.excreted by kidneys
4.diffuses from blood into the milk
>milk urea nitrogen (MUN); can be tested by test strip

Question 27

Non-protein Nitrogen max in feed

Answer 27

-can feed up to 30% of total diet nitrogen as non-protein nitrogen

Question 28

Issues with feeding too high non-protein nitrogen

Answer 28

-palatability
-reduces microbial growth= protein synthesis
-energy cost to convert absorbed NH3 to urea

Question 29

Ammonia toxicity

Answer 29

-when high levels of non-protein nitrogen occurs
-called bovine bonkers; incoordination, salivation , tremors

Question 30

Treatment of high levels of non-protein nitrogen

Answer 30

-NH3 is rapidly absorbed from rumen but NH4 is not
-acidic pH=more NH4 than NH3
-stomach tube with vinegar

Question 31

Carbohydrate and nitrogen balance =microbial protein synthesis

Answer 31

-need 3 inputs
1.energy
2.carbon skeleton
3.ammonia (nitrogen)
-if you have rapidly fermented carbohydrates (starch and sugars) diet then requires rapidly available N (urea)
-if you have slowly fermented carbohydrates (cellulose and hemicellulose)
>then require N that is more slowly digested (eg.soybean meal or canola meal)