2. GI Part 10 Flashcards
why are proteins vulnerable to fermentation
they are made of carbon compounds that cna be further reduced to provide energy for anaerobic microbes
what do microbes produce and what do they form as end products
where are these end products absorbed
microbes produce endopeptidases that form short chain peptides as end products
these peptides are absorbed into microbial cell bodies
what are peptides used for in the microbial cell
used to form microbial protein or can be further digested for energy production via VFA pathway
describe protein metabolism by rumen microbes
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
what must happen for an amino acid to enter VFA pathway
the amino acid must deaminate
what happens to amino acid when it is deaminated
amino acid –> NH3 + carbon skeleton
can carbon structures of all amino acids be directly used for VFA synthesis
most can
exception – BCAA
valine + 2 H2O –>
isobutyrate + NH3 + CO2
leucine + 2 H2O –>
isovalerate + NH3 + CO2
isoleucine + 2 H2O –>
2-methylbutyrate + NH3 + CO2
what does the ruminant depend on to meet its needs
microbial protein – because almost all dietary protein is fermented in the rumen
what are the 2 options for ruminants to meet their protein needs
- microbes washed out of the rumen –> microbial protein reaching the abomasum and the small intestine
- protein can be produced in the rumen from protein and non protein sources like ammonia, nitrates, urea
what is urea
the nitrogen waste product of protein catabolism
what are the 2 sources that urea is synthesized from in the liver
- urea coming from deamination of endogenous amino acids
2. nitrogen absorbed as ammonia from the rumen by rumen epithelium
where is urea excreted in monogastric animals
where in ruminants
monogastric – kidney
ruminants – kidney, rumen
what happens to some of the urea that reaches the rumen
what conditions does this happen under
it can be resynthesized into protein that will contribute to amino acid needs of host animal
under conditions of low dietary protein – conserve nitrogen
are fats and lipids common in cow diets
no
are fats common plants
what is excerption
no <5% dry matter
exception is oilseeds
what enzymes do microbes produces for lipid digestion
lipases
phospholipases
what kind of fat is in cattle diets
PUFA
where are triglycerides found
cereal grains oilseeds animal fats byproduct feeds milk (milk fat)
where are glycolipids found
forages
where are phospholipids found
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
where are FFA found
minor component in dairy feeds
major component of certain fat supplements
what results from fat being hydrolyzed by microbial lipases
what do they go on to make
glycerol, sugars –> VFA
FFA –> hydrogenation (biohydrogenation)
where do FA synthesized in rumen go
pass to abomasum and small intestine for absorption
what is the ruminant acetic/propionic/butyric acid concentration ratio for
high forage diets
high grain diets
high forage diets – 70:20:10
high grain diets – 60:30:10
is total acetate higher in high grain or high forage diets
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
what vitamins do microbes synthesize
C
K
B – B1 (thiamin), B12 (cobalamin)
when do you see a thiamin deficiency
after a sudden change of feed form roughage to concentrate
when do you see a cobalamin deficiency
cobalt poor soils
using diets with too much grain
young ruminants and microbial vitamin synthesis
relatively small fermentative activity in young ruminants – cannot synthesize vitamins and need them in diet
what are the 2 main mechanisms of VFA absorption in the rumen epithelium
- ionized VFA (Ac-) –> cannot diffuse, need a carrier (HCO3-/Ac- antiport)
- non ionized (HAc) –> lipophilic and can diffuse through apical membrane
how does rumen acidosis occur
fast fermentable carbs (starch rich diet) leads to increase in VFA production –> pH in rumen gets more acidic (lower)
what does the pKa indicate
what is pKa of VFA
the pH at which a substance is 50% ionized and 50% non ionized
pKa of VFA – 4.8
what does the acidic pH of the rumen stimulate
proliferation of lactate producing bacteria –> exacerbation of the acidosis
describe absorption of chloride in the rumen
- Cl-/HCO3- exchanger
2. basolateral channel (not fully identified)
describe potassium absorption in the rumen
- apical and basolateral channels
2. high luminal K+ concentration (transepithelial potential difference)
describe absorption of magnesium in the rumen
- electrogenic transport – Mg2+ channel (dependent on potential difference between apical/basolateral side)
what is magnesium absorption in the rumen affected by
affected in the presence of high K+ concentrations (young pastures or potassium fertilized pastures) – leads to pasture grass tetany
clinical signs of pasture grass tetany
irritability msucle twitching staring incoordination staggering collapse thrashing head thrown back coma death
describe the absorption of calcium in the rumen
reabsorption not fully understood
- probably electroneutral (Ca/H exchanger, not fully understood)
- basolateral Na/Ca exchanger and Ca ATPase
describe the omasum
comprised of muscular folds (leaves) that project form the greater curvature into the lumen
canal connects the reticulum with the abomasum
functions of the omasum (4)
- concentration of ingesta (absorption of water)
- SCFA (VFA) absorption (diffusion more relevant here)
- Na+ and Cl- absorption
- HCO3- reabsorption
