Module 7- Nutrient digestibility Flashcards
digestibility
proportion of a feed that is not excreted in feces and therefore assumed to be absorbed
what is the major determinant of nutritional value of feeds
digestibility
high digestibility = ( ) nutrient retention = ( ) performance
high, high
3 ways to measure feed digestibility + example for each
1) in vivo
- total fecal collections
- indicator method
2) in situ
- nylon bag
3) in vitro
- tilley & terry method
nylon bag technique
feed is contained in nylon bag & placed in rumen
in situ means
between in vivo + in vitro
why is an adaptation period required for in vivo digestibility measurement? (3)
1) need time for residual feed from previous diet to be totally excreted
- takes several days for ruminants
2) GI tract needs to adapt
3) adapt to new environment
why is a balloon inflated with distilled water in bladder catheter for total urine collection?
so catheter stays in place
metabolism crates only use what sex of animal? why?
male, urine is diverted into funnel below crate
adaptation period for metabolism stalls vs crates
stalls: 4-14
crates: 2-3 days
issues with digestibility harness
bags fill up fast & become heavy
- more labour to empty bags frequently
true digestibility is always going to be ( ) than apparent digestibility. why?
higher, bc of sloughed off epithelial cells/enzymes
- overestimating proteins in feces
what is the protein in feces? (2)
undigested protein from feed & endogenous protein
NDF will always use ( ) digestibility bc no NDF secreted in GI tract
true
indirect measurement of digestibility
use basal diet digestibility & compare with test ingredient digestibility
associative effects of indirect measurement of digestibility (problem)
assumes digestibility of test ingredient stays at that % when mixed with other ingredients
2 problems with total collections
1) accurate estimate of feed intake
2) must collect ALL fecal output
measuring digestibility with the indicator method
add indicator to feed at low level & measure the concentration in the feces
indicator is often added at (%)
0.5
steady state
consistent feed intake & fecal output
DM digestibility using indicator/marker =
100 - (% indicator in feed) x 100) / (% indicator in feces)
specific nutrient digestibility =
100 - (% indicator in feed) x (% nutrient in feces ) x 100 / (% indicator in feces) x (% nutrient in feed)
concentration of indicator in the feces is always going to be ( ) than it is in the feed. why?
greater, as feed gets digested = concentrates indicator
7 properties of an ideal indicator or marker
1) cannot be digested/absorbed
2) no negative impacts
3) associated with material that it is to mark
4) uniformly excreted in feces each time
5) inexpensive
6) readily available
7) easily detected / easy to measure
2 types of digestibility markers + examples
1) internal markers -> already contained in test feed
- lignin
2) external markers -> chemical added to test feed
- chromic oxide
most common external marker used
chromic oxide
what 2 methods stimulate rumen fermentation & gastric digestion under controlled environments?
in vitro & in situ
tilley & terry method
done in test tube
1) incubation of rumen fluid
2) 2nd incubation with pepsin
why is a buffer needed in the tilley & terry method
microorganims in rumen have optimal environment that they can survive in
what environment is the tilley & terry method done in? why?
anaerobic bc microorganisms are anaerobic
purpose of incubating with pepsin in the tilley & terry method
mimics what goes on after the rumen
IVDMD
in vitro dry matter digestibility
IVDMD =
100% x [(initial dry sample weight - (residue - blank))/ initial dry sample weight
tilley & terry method uses what kind of flask
blank
what does the blank flask contain in the tilley & terry method
rumen fluid + buffer
why does the tilley & terry method not add test feed to the flask?
cannot get rid of residual feed from donor cow rumen fluid
advantage & disadvantage of the tilley & terry method
advantage: process very large numbers quickly
disadvantage: rumen fluid exposure to atmospheric air can kill microorganisms
typical length of incubation in tilley & terry method
48 hours, but can be 24 for highly digestible feeds
purpose of shaking apparatus in tilley & terry method
need rumen fluid & test feed to be continuously mixed
nylon bag pore size
50 microns -> do not want any feed to escape that is not through digestion
how are DM or residues determined in the nylon bag method
rinse bags under water & put in oven
graph for rate of digestion of feed ingredients for nylon bag method: X vs Y axis
X axis: time for DM to disappear from bags
Y axis: % disappeared
mobile nylon bag technique
- used to determine mostly forage digestibility
- mimics digestion in stomach by incubating bags with pepsin & HCI and then incubating into duodenum
where is the mobile nylon bag placed inside pigs?
proximal duodenum
what is it called when you do the nylon bag method in pigs?
mobile nylon bag technique
effect of fiber on energy digestibility
increase in fiber content = decrease digestibility
- mature plants
- reduces ability for enzymes to penetrate cell wall = less digestibility
why does lignin decrease digestibility?
it binds everything together
as plants mature, fiber content will
increase
effects of feed processing on digestibility
improves digestibility bc increases surface area for enzymes to do their work
there is a bigger response when you grind ( ) quality feeds compared to ( ) quality feeds
lower, higher
lower feed conversion =
better efficiency bc less feed required for animal to gain weight
oat vs wheat : quality
oat is lower quality than wheat
too small of particle size ( ) digestibility. why?
reduces, increased passage rate
what feeds can contain trypsin inhibitor, tannins, and glucosinolates
trypsin inhibitors: raw soybeans
tannins: faba beans
glucosinolates: rapeseed (canola)
phytases in monogastrics vs ruminants on feed digestibility
reduces feed digestibility
why is phytase added to monogastric diets?
to break down phytate to release P
phytase improves P digestibility in
cereal grains
enviropig
could digest phytate P
what is the major advantage ruminants have with fibre digestibility?
presence of microorganisms that can digest cellulose & hemicellulose
why do pigs not get a lot out of fiber?
bc they do not have a large enough fermentation chamber
as animals get older, their ability to digest feed ( ). why?
improves, higher expression of enzymes
what is the exception to increasing enzyme expression with age?
lactase -> it diminishes as animals are weaned
high levels of fiber intake will ( ) passage rate and ( ) digestibility
increase, decreases
why does digestibility decrease in 4x maintenance?
bc animal is eating more feed so passage rate increases & reduces digestibility
animals exposed to cold weather will have ( ) digestibility. why?
decreased, bc higher level of DMI=higher passage rate
fiber digestibility ( ) in summer. why?
decreases, consuming more water = increases passage rate
