Hindgut Fermentative Digestion

Question 1

ruminants digest fiber ___ to glandular/auto-enzyme digestion (before/after)

Answer 1

prior to

Question 2

almost all vertebrates facilitate bacterial digestion ___ auto-enzyme digestion (before/after)

Answer 2

after

Question 3

describe fiber digestion PRIOR to auto-enzymatic digestion in foregut fermenters

Answer 3

allows use of bacterial biomass
detoxify bacteria
upgrade NPN
downgrade high quality protein
loss of CHO

Question 4

what’s what’s the nutritional advantage of foregut fermentation?

Answer 4

bacterial products formed before enzyme digestion, so bacterial protein and products can be used to help with detoxification
endogenous N products - urea can be recycled

Question 5

describe bacterial digestion AFTER auto-enzymatic digestion in hindgut fermenters

Answer 5

more efficient use of substrates that can be auto digested
acid Tx helps breakdown CHO
loss of microbial protein since it does not pass stomach and Si

Question 6

what’s the nutritional advantage of hindgut fermentation?

Answer 6

use of easy digestable substrates
less problems with diet shift
NO further mechanical digest
microbial protein lost

Question 7

what are the two classifications of hindgut fermenters?

Answer 7

cecal and colonic

Question 8

list cecal fermenters

Answer 8

rabbit
guinea pig
chinchilla
rat

Question 9

what type of fermenter are large nonruminant herbivores (horse, rhino, gorilla)?

Answer 9

colon

Question 10

where do omnivores have hindgut fermentation?

Answer 10

sacculated colons

Question 11

what two functions are needed for hindgut fermentation?

Answer 11

water flow
optimal microbe growth and VFA production conditions

Question 12

water in LI follows ___ absorption

Answer 12

VFA

Question 13

where is most water absorbed?

Answer 13

cecum

Question 14

describe water secretion into the LI

Answer 14

1. Na-K-Cl cotransport moves Cl into cell by basolateral membrane
2. apical Cl channel (CFTR) secretes Cl into lumen
3. Na move paracellular to lumen, water follows
4. Na-K pump maintains gradient

Question 15

what is CFTR?

Answer 15

cystic fibrosis transmembrane conductance regulator
transports Cl from inside of cell to outside, with Na following paracellularly

Question 16

describe water absorption from LI

Answer 16

1. water follows VFA
2. Na/H exchanger and parallel Cl/bicarb exchanger, water also follows the NaCl absorb
3. water absorbed paracellularly, AQP on both sides

Question 17

list the optimal conditions for microbial growth and VFA production/absorption

Answer 17

substrate
pH, osmolarity, anaerobiosis
remove waste
space and time

Question 18

list the main substrate supplies for LI fermentation

Answer 18

CHO
protein and NPN (urea)

Question 19

how is LI pH maintained?

Answer 19

secrete bicarb and phosphate in ileum and removal of waste, absorb VFA and lactate

Question 20

what’s a main waste product of fermentation?

Answer 20

VFA
energy source for host, absorbed in cecum and colon

Question 21

how is the ionized form of VFA absorbed?

Answer 21

VFA-bicarb antiporter

Question 22

how is undissociated VFA absorbed?

Answer 22

lipophilic diffusion

Question 23

VFA and Na absorption leads to ___ absorption of water

Answer 23

osmotic

Question 24

why are there two VFA absorption mechanisms (ionized vs undissociated)?

Answer 24

since pH fluctuates
pK for VFA is 4.8, but colon pH varies

Question 25

what VFA form does colon pH > pK favor?

Answer 25

ionized VFA

Question 26

what VFA form does pH = pK favor in colon?

Answer 26

protonated

Question 27

define selective retention

Answer 27

fermenting based on size and residue of particles in cecum/colon

Question 28

list the three locations of selective retention

Answer 28

Question 29

describe the cecal constriction location of selective retention

Answer 29

very small transition from cecum to R ventral colon, causing increased P so only small particles can get through

Question 30

what orifice is utilized during cecal constriction?

Answer 30

cecocolic

Question 31

describe cecal motility in horse

Answer 31

1. contraction begins in cecal body near apex
2. contractions move towards base to create P gradient and form constriction before ileocecal papilla
3. elevation of floow of cecal base and opening of cecocolic ostium
4. contract cranial compartment of cecal base so ingesta/gas moves

Question 32

describe flexure pelvina location of selective retention

Answer 32

V and D colon are distinct compartments of delaying progression of ingesta, so selectively keeps larger particles

Question 33

describe the R D colon location of selective retention

Answer 33

R D colon is large, transverse colon is small, so narrow path for only fine particles and fluid

Question 34

where does sand colic occur?

Answer 34

R D colon
lack of constriction = died dead

Question 35

how does retention of fermentating material and mixing in V colon occur?

Answer 35

peristalsis - change from wide to narrow to cause squeeze of pelvic flexure
antiperistalsis

Question 36

what does haustral segmentation do in V colon?

Answer 36

mixes ingesta and increases retention time
increase time for fermentation and VFA absorb
involves taenia and circular muscle

Question 37

food particle size determines…

Answer 37

retention time

Question 38

explain grain overfeeding in horses

Answer 38

grain is rich in fast hydrolyzable nutrients
overload causes maxing out of GI ability in SI, so undigested material goes into LI
too much gas produced, accumulates

Question 39

what is tympany in terms of grain overload?

Answer 39

distended GI tract due to gas accumulation
causes colic, GI hypoperfusion, respiratory distress