Module 7- Nutrient digestibility

Question 1

digestibility

Answer 1

proportion of a feed that is not excreted in feces and therefore assumed to be absorbed

Question 2

what is the major determinant of nutritional value of feeds

Answer 2

digestibility

Question 3

high digestibility = ( ) nutrient retention = ( ) performance

Answer 3

high, high

Question 4

3 ways to measure feed digestibility + example for each

Answer 4

1) in vivo
- total fecal collections
- indicator method
2) in situ
- nylon bag
3) in vitro
- tilley & terry method

Question 5

nylon bag technique

Answer 5

feed is contained in nylon bag & placed in rumen

Question 6

in situ means

Answer 6

between in vivo + in vitro

Question 7

why is an adaptation period required for in vivo digestibility measurement? (3)

Answer 7

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

Question 8

why is a balloon inflated with distilled water in bladder catheter for total urine collection?

Answer 8

so catheter stays in place

Question 9

metabolism crates only use what sex of animal? why?

Answer 9

male, urine is diverted into funnel below crate

Question 10

adaptation period for metabolism stalls vs crates

Answer 10

stalls: 4-14
crates: 2-3 days

Question 11

issues with digestibility harness

Answer 11

bags fill up fast & become heavy
- more labour to empty bags frequently

Question 12

true digestibility is always going to be ( ) than apparent digestibility. why?

Answer 12

higher, bc of sloughed off epithelial cells/enzymes
- overestimating proteins in feces

Question 13

what is the protein in feces? (2)

Answer 13

undigested protein from feed & endogenous protein

Question 14

NDF will always use ( ) digestibility bc no NDF secreted in GI tract

Answer 14

true

Question 15

indirect measurement of digestibility

Answer 15

use basal diet digestibility & compare with test ingredient digestibility

Question 16

associative effects of indirect measurement of digestibility (problem)

Answer 16

assumes digestibility of test ingredient stays at that % when mixed with other ingredients

Question 17

2 problems with total collections

Answer 17

1) accurate estimate of feed intake
2) must collect ALL fecal output

Question 18

measuring digestibility with the indicator method

Answer 18

add indicator to feed at low level & measure the concentration in the feces

Question 19

indicator is often added at (%)

Answer 19

0.5

Question 20

steady state

Answer 20

consistent feed intake & fecal output

Question 21

DM digestibility using indicator/marker =

Answer 21

100 - (% indicator in feed) x 100) / (% indicator in feces)

Question 22

specific nutrient digestibility =

Answer 22

100 - (% indicator in feed) x (% nutrient in feces ) x 100 / (% indicator in feces) x (% nutrient in feed)

Question 23

concentration of indicator in the feces is always going to be ( ) than it is in the feed. why?

Answer 23

greater, as feed gets digested = concentrates indicator

Question 24

7 properties of an ideal indicator or marker

Answer 24

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

Question 25

2 types of digestibility markers + examples

Answer 25

1) internal markers -> already contained in test feed - lignin 2) external markers -> chemical added to test feed - chromic oxide

Question 26

most common external marker used

Answer 26

chromic oxide

Question 27

what 2 methods stimulate rumen fermentation & gastric digestion under controlled environments?

Answer 27

in vitro & in situ

Question 28

tilley & terry method

Answer 28

done in test tube 1) incubation of rumen fluid 2) 2nd incubation with pepsin

Question 29

why is a buffer needed in the tilley & terry method

Answer 29

microorganims in rumen have optimal environment that they can survive in

Question 30

what environment is the tilley & terry method done in? why?

Answer 30

anaerobic bc microorganisms are anaerobic

Question 31

purpose of incubating with pepsin in the tilley & terry method

Answer 31

mimics what goes on after the rumen

Question 32

IVDMD

Answer 32

in vitro dry matter digestibility

Question 33

IVDMD =

Answer 33

100% x [(initial dry sample weight - (residue - blank))/ initial dry sample weight

Question 34

tilley & terry method uses what kind of flask

Answer 34

blank

Question 35

what does the blank flask contain in the tilley & terry method

Answer 35

rumen fluid + buffer

Question 36

why does the tilley & terry method not add test feed to the flask?

Answer 36

cannot get rid of residual feed from donor cow rumen fluid

Question 37

advantage & disadvantage of the tilley & terry method

Answer 37

advantage: process very large numbers quickly disadvantage: rumen fluid exposure to atmospheric air can kill microorganisms

Question 38

typical length of incubation in tilley & terry method

Answer 38

48 hours, but can be 24 for highly digestible feeds

Question 39

purpose of shaking apparatus in tilley & terry method

Answer 39

need rumen fluid & test feed to be continuously mixed

Question 40

nylon bag pore size

Answer 40

50 microns -> do not want any feed to escape that is not through digestion

Question 41

how are DM or residues determined in the nylon bag method

Answer 41

rinse bags under water & put in oven

Question 42

graph for rate of digestion of feed ingredients for nylon bag method: X vs Y axis

Answer 42

X axis: time for DM to disappear from bags Y axis: % disappeared

Question 43

mobile nylon bag technique

Answer 43

- used to determine mostly forage digestibility - mimics digestion in stomach by incubating bags with pepsin & HCI and then incubating into duodenum

Question 44

where is the mobile nylon bag placed inside pigs?

Answer 44

proximal duodenum

Question 45

what is it called when you do the nylon bag method in pigs?

Answer 45

mobile nylon bag technique

Question 46

effect of fiber on energy digestibility

Answer 46

increase in fiber content = decrease digestibility - mature plants - reduces ability for enzymes to penetrate cell wall = less digestibility

Question 47

why does lignin decrease digestibility?

Answer 47

it binds everything together

Question 48

as plants mature, fiber content will

Answer 48

increase

Question 49

effects of feed processing on digestibility

Answer 49

improves digestibility bc increases surface area for enzymes to do their work

Question 50

there is a bigger response when you grind ( ) quality feeds compared to ( ) quality feeds

Answer 50

lower, higher

Question 51

lower feed conversion =

Answer 51

better efficiency bc less feed required for animal to gain weight

Question 52

oat vs wheat : quality

Answer 52

oat is lower quality than wheat

Question 53

too small of particle size ( ) digestibility. why?

Answer 53

reduces, increased passage rate

Question 54

what feeds can contain trypsin inhibitor, tannins, and glucosinolates

Answer 54

trypsin inhibitors: raw soybeans tannins: faba beans glucosinolates: rapeseed (canola)

Question 55

phytases in monogastrics vs ruminants on feed digestibility

Answer 55

reduces feed digestibility

Question 56

why is phytase added to monogastric diets?

Answer 56

to break down phytate to release P

Question 57

phytase improves P digestibility in

Answer 57

cereal grains

Question 58

enviropig

Answer 58

could digest phytate P

Question 59

what is the major advantage ruminants have with fibre digestibility?

Answer 59

presence of microorganisms that can digest cellulose & hemicellulose

Question 60

why do pigs not get a lot out of fiber?

Answer 60

bc they do not have a large enough fermentation chamber

Question 61

as animals get older, their ability to digest feed ( ). why?

Answer 61

improves, higher expression of enzymes

Question 62

what is the exception to increasing enzyme expression with age?

Answer 62

lactase -> it diminishes as animals are weaned

Question 63

high levels of fiber intake will ( ) passage rate and ( ) digestibility

Answer 63

increase, decreases

Question 64

why does digestibility decrease in 4x maintenance?

Answer 64

bc animal is eating more feed so passage rate increases & reduces digestibility

Question 65

animals exposed to cold weather will have ( ) digestibility. why?

Answer 65

decreased, bc higher level of DMI=higher passage rate

Question 66

fiber digestibility ( ) in summer. why?

Answer 66

decreases, consuming more water = increases passage rate