2. GI Part 10

Question 1

why are proteins vulnerable to fermentation

Answer 1

they are made of carbon compounds that cna be further reduced to provide energy for anaerobic microbes

Question 2

what do microbes produce and what do they form as end products
where are these end products absorbed

Answer 2

microbes produce endopeptidases that form short chain peptides as end products

these peptides are absorbed into microbial cell bodies

Question 3

what are peptides used for in the microbial cell

Answer 3

used to form microbial protein or can be further digested for energy production via VFA pathway

Question 4

describe protein metabolism by rumen microbes

Answer 4

proteases on microbe surface generate peptides from proteins

intracellularly, peptides are hydrolyzed to amino acids

amino acids contributes to synthesis of microbial protein and synthesis of VFA and ammonia

amino acids are also synthesized intracellularly from NH3 and VFA

Question 5

what must happen for an amino acid to enter VFA pathway

Answer 5

the amino acid must deaminate

Question 6

what happens to amino acid when it is deaminated

Answer 6

amino acid –> NH3 + carbon skeleton

Question 7

can carbon structures of all amino acids be directly used for VFA synthesis

Answer 7

most can

exception – BCAA

Question 8

valine + 2 H2O –>

Answer 8

isobutyrate + NH3 + CO2

Question 9

leucine + 2 H2O –>

Answer 9

isovalerate + NH3 + CO2

Question 10

isoleucine + 2 H2O –>

Answer 10

2-methylbutyrate + NH3 + CO2

Question 11

what does the ruminant depend on to meet its needs

Answer 11

microbial protein – because almost all dietary protein is fermented in the rumen

Question 12

what are the 2 options for ruminants to meet their protein needs

Answer 12

1. microbes washed out of the rumen –> microbial protein reaching the abomasum and the small intestine
2. protein can be produced in the rumen from protein and non protein sources like ammonia, nitrates, urea

Question 13

what is urea

Answer 13

the nitrogen waste product of protein catabolism

Question 14

what are the 2 sources that urea is synthesized from in the liver

Answer 14

1. urea coming from deamination of endogenous amino acids

2. nitrogen absorbed as ammonia from the rumen by rumen epithelium

Question 15

where is urea excreted in monogastric animals

where in ruminants

Answer 15

monogastric – kidney

ruminants – kidney, rumen

Question 16

what happens to some of the urea that reaches the rumen

what conditions does this happen under

Answer 16

it can be resynthesized into protein that will contribute to amino acid needs of host animal

under conditions of low dietary protein – conserve nitrogen

Question 17

are fats and lipids common in cow diets

Answer 17

no

Question 18

are fats common plants

what is excerption

Answer 18

no <5% dry matter

exception is oilseeds

Question 19

what enzymes do microbes produces for lipid digestion

Answer 19

lipases

phospholipases

Question 20

what kind of fat is in cattle diets

Answer 20

PUFA

Question 21

where are triglycerides found

Answer 21

cereal grains
oilseeds
animal fats
byproduct feeds
milk (milk fat)

Question 22

where are glycolipids found

Answer 22

forages

Question 23

where are phospholipids found

Answer 23

minor component of most feeds

form cell membrane of all animal cells and surface of milk fat globules

important in fat digestion in small intestine of cows

Question 24

where are FFA found

Answer 24

minor component in dairy feeds

major component of certain fat supplements

Question 25

what results from fat being hydrolyzed by microbial lipases what do they go on to make

Answer 25

glycerol, sugars --> VFA FFA --> hydrogenation (biohydrogenation)

Question 26

where do FA synthesized in rumen go

Answer 26

pass to abomasum and small intestine for absorption

Question 27

what is the ruminant acetic/propionic/butyric acid concentration ratio for high forage diets high grain diets

Answer 27

high forage diets -- 70:20:10 | high grain diets -- 60:30:10

Question 28

is total acetate higher in high grain or high forage diets

Answer 28

percentage of acetate is lower in high starch diet (high grain), the total amount is considerably greater than the high fiber diet -- more total VFA produced

Question 29

what vitamins do microbes synthesize

Answer 29

C K B -- B1 (thiamin), B12 (cobalamin)

Question 30

when do you see a thiamin deficiency

Answer 30

after a sudden change of feed form roughage to concentrate

Question 31

when do you see a cobalamin deficiency

Answer 31

cobalt poor soils using diets with too much grain

Question 32

young ruminants and microbial vitamin synthesis

Answer 32

relatively small fermentative activity in young ruminants -- cannot synthesize vitamins and need them in diet

Question 33

what are the 2 main mechanisms of VFA absorption in the rumen epithelium

Answer 33

1. ionized VFA (Ac-) --> cannot diffuse, need a carrier (HCO3-/Ac- antiport) 2. non ionized (HAc) --> lipophilic and can diffuse through apical membrane

Question 34

how does rumen acidosis occur

Answer 34

fast fermentable carbs (starch rich diet) leads to increase in VFA production --> pH in rumen gets more acidic (lower)

Question 35

what does the pKa indicate what is pKa of VFA

Answer 35

the pH at which a substance is 50% ionized and 50% non ionized pKa of VFA -- 4.8

Question 36

what does the acidic pH of the rumen stimulate

Answer 36

proliferation of lactate producing bacteria --> exacerbation of the acidosis

Question 37

describe absorption of chloride in the rumen

Answer 37

1. Cl-/HCO3- exchanger | 2. basolateral channel (not fully identified)

Question 38

describe potassium absorption in the rumen

Answer 38

1. apical and basolateral channels | 2. high luminal K+ concentration (transepithelial potential difference)

Question 39

describe absorption of magnesium in the rumen

Answer 39

1. electrogenic transport -- Mg2+ channel (dependent on potential difference between apical/basolateral side)

Question 40

what is magnesium absorption in the rumen affected by

Answer 40

affected in the presence of high K+ concentrations (young pastures or potassium fertilized pastures) -- leads to pasture grass tetany

Question 41

clinical signs of pasture grass tetany

Answer 41

``` irritability msucle twitching staring incoordination staggering collapse thrashing head thrown back coma death ```

Question 42

describe the absorption of calcium in the rumen

Answer 42

reabsorption not fully understood 1. probably electroneutral (Ca/H exchanger, not fully understood) 2. basolateral Na/Ca exchanger and Ca ATPase

Question 43

describe the omasum

Answer 43

comprised of muscular folds (leaves) that project form the greater curvature into the lumen canal connects the reticulum with the abomasum

Question 44

functions of the omasum (4)

Answer 44

1. concentration of ingesta (absorption of water) 2. SCFA (VFA) absorption (diffusion more relevant here) 3. Na+ and Cl- absorption 4. HCO3- reabsorption