Rumen Metabolism

Question 1

what is the major type of rumen microflora

Answer 1

bacteria

Question 2

what do microbes use as substrates

Answer 2

carbon and nitrogen

Question 3

what kind of environment do microbes need

Answer 3

acidic (pH 6.6-6.8)
anaerobic
reduced (minimal reducing agents)

Question 4

are microbes efficient at using fat

Answer 4

no - will need to hydrogenate NEFAs/unsaturated FA before incorporating into cell membranes to prevent kinks

diets should be 3-5% fat

Question 5

what do microbes produce

Answer 5

VFAs and protein

Question 6

what are the main 3 VFAs produced by microbes

Answer 6

acetate > propionate > butyrate

Question 7

how many carbons are each of the VFAs

Answer 7

acetate: 2C
propionate: 3C
butyrate: 4C

Question 8

what component of the plant cell wall is not able to be broken down by microbes

Answer 8

lignin

becomes more abundant in plants as they get older/dried

Question 9

what are the steps of carbohydrate fermentation

Answer 9

1. microbes secrete enzymes that break down polysaccharides into monosaccharides (extracellular)
2. monosaccharides enter glycolysis to form pyruvate
3. pyruvate + ATP + reducing equivalents [H] forms VFAs + ATP + methane + CO2

Question 10

what is the function of reducing equivalents

Answer 10

carry unionized hydrogens (NADH, NADPH, FADH, etc) that are required for substrate level phosphorylation

Question 11

what is substrate level phosphorylation

Answer 11

anaerobic phosphorylation in the rumen

produces 2 acetates + 2 CO2 + 8 [H] + 4 ATP

Question 12

what happens to the 8 reducing equivalents produced by substrate level phosphorylation

Answer 12

they get used by methanogens to produce methane

need to get used in order to maintain reduced environment

Question 13

how are VFAs absorbed across the rumen

Answer 13

binding free ionized H+

it does this to act as a buffer - picking up free H+ prevents rumen acidosis

Question 14

why does the rumen need to be kept in a reduced (low [H]) environment

Answer 14

reduced environment favors ATP and VFA production because ATP/VFA production also generates [H], so if the rumen was high in [H] then ATP/VFA production would slow

need methanogens to maintain the reduced environment so that VFAs can get produced

Question 15

acetate production

Answer 15

hexose + ADP –> 2 acetate + 2CO2 + 8 [H] + 4 ATP

Question 16

propionate production (from succinate)

Answer 16

most common pathway because it generates more energy

hexose + ADP + 4 [H] –> 2 propionate + 4 ATP

Question 17

propionate production (from lactate)

Answer 17

less common pathway because it generates less energy

hexose + ADP + [H] –> 2 propionate + 2 ATP

Question 18

butyrate production

Answer 18

hexose + ADP –> butyrate + 2 CO2 + 4 [H] + 3 ATP

Question 19

can there ever be more propionate in the rumen than acetate

Answer 19

NO because propionate production requires [H]

relies on acetate and butyrate production to produce [H]

Question 20

can there ever be more propionate in the rumen than butyrate

Answer 20

yes because butyrate production is used less than acetate since it yields less ATP and [H], so the [H] produced during acetate production is enough to facilitate propionate production

Question 21

what are the gases produced by the microbes

Answer 21

1. CO2 - majority
2. CH4 - produced by methanogens from [H]
3. H2 - minimal (reducing agent, gets rapidly used)
4. H+ - released from VFAs and lactic acid; will inhibit methanogens

Question 22

can methanogens work in too acidic of an environment

Answer 22

no - get inhibited by H+

Question 23

what does the rumen produce on a forage (grazing) diet

Answer 23

• significantly more acetate than propionate
• high hexose
• high methane
• 75% VFAs

Question 24

what does the rumen produce on a grain (feedlot) diet

Answer 24

• almost equal amounts of acetate and propionate
• low hexose
• low methane
• 85% VFAs

Question 25

what do ionophores do

Answer 25

stalls gram positive rumen bacteria by "poking holes" in their membranes --> requires them to devote more energy toward fixing holes than producing VFAs --> allows starch digesters (gram neg) to grow --> releases more [H] --> promotes propionate production

Question 26

how does starch affect the diet

Answer 26

starch = high grain diet promotes lactic acid production which increases free H+ ions --> inhibits methanogens

Question 27

how do unsaturated FA affect the diet

Answer 27

toxic to microbes - requires hydrogenation before it can be used --> uses up [H] --> methanogens unable to use [H] --> decreases methane production

Question 28

what are the steps of protein digestion in the rumen

Answer 28

proteins --> AAs amino acids get catabolized into ammonia and carbon skeletons components are able to get used to reform whatever amino acids the animal needs

Question 29

what is nitrogen recycling in the rumen

Answer 29

ammonia travels to the liver to get converted to urea which can get recycled during rumination (in saliva) and reused for its nitrogen

Question 30

is the rumen well adapted for high nitrogen conditions

Answer 30

yes, there are many ways the rumen can use excess N

Question 31

what hydrolyzes triglycerides in the rumen

Answer 31

microbial lipases

Question 32

are cows hyper or hypoglycemic normally

Answer 32

hypoglycemic --> requires mechanisms to converse glucose in the body

Question 33

what mechanisms are there to converse glucose

Answer 33

1. acetate is the primary energy source (not glucose) 2. propionate is used for gluconeogenesis 3. liver is dedicated primarily to gluconeogenesis (compartmentalization) 4. butyrate is oxidized by rumen wall to form ketones or used for FA synthesis

Question 34

gluconeogenesis in ruminants

Answer 34

occurs in the liver substrates: propionate and glucogenic AA

Question 35

FA synthesis in ruminants

Answer 35

occurs in adipose tissue (NOT liver) - produces lactate --> high lactate in liver - lipid transport is primarily HDL substrate: acetate

Question 36

what is compartmentalization

Answer 36

the liver does NOT have the enzymes needed for FA synthesis (citrate lyase + malic enzyme) allows liver to be dedicated to gluconeogenesis

Question 37

what does starvation in ruminants refer to

Answer 37

lack of glucose; can be caused by: 1. lack of propionate 2. lack of glucogenic AAs 3. liver dysfunction

Question 38

what is the process of developing ketosis

Answer 38

starvation --> increased FA mobilization --> partial FA metabolism (lack of glucose prevents complete metabolism) --> produces ketones instead --> ketosis

Question 39

primary vs secondary ketosis

Answer 39

primary: occurs due to lack of food (ex. did not get fed) secondary: occurs due to underlying primary disease that prevents the animal from being able to eat (ex. lameness)

Question 40

diagnosing ketosis

Answer 40

hypoglycemia + elevated ketones

Question 41

how to prevent ketosis

Answer 41

high grain/starch diet administer glucose precursors consistent feeding