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Nutrition > Feedstuff Evaluation > Flashcards

Feedstuff Evaluation Flashcards

1
Q

what 4 things do you need to know when evaluating a feedstuff?

A
  1. nutrient composition
  2. presence of toxins
  3. palatability
  4. digestibility/nutrient availability
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2
Q

values of nutrient content of a sample are of no practical use unless?

A

the sample tested is representative of the feedstuff as it is fed to animals

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3
Q

how do you sample hay?

A

with a hay probe; stick into center of bale and get 12-20 total samples

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4
Q

how do you sample grass/pastures?

A

use a 1ft by 1ft square pipe; throw it, and collect areas at grazing height where it lands; repeat 12-20 times

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5
Q

how do you sample grain?

A

use a grain probe in the center of the grain bin 12-20 times

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6
Q

what is feed microscopy used for?

A

regulatory purposes; to make sure the feedstuff is actually made of what it claims to be

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7
Q

is feed microscopy very useful as a method of evaluation?

A

no; can check for presence of toxins or molds and such but nutrients are not visible so is not very useful

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8
Q

what is the proximate analysis of feeds?

A

a standard system of chemical methods of feed analysis; old but inexpensive so is widely used

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9
Q

what are the 5 aspects of proximate feed analysis?

A
  1. dry matter
  2. crude protein
  3. ether extract/crude fat
  4. ash
  5. crude fiber
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10
Q

describe the dry matter portion of proximate feed analysis

A

drying feed sample to a constant weight to determine water content

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11
Q

what does removing the water from a feedstuff allow for?

A

comparisons of nutrient content between different feedstuffs

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12
Q

what aspect of proximate feed analysis is always performed first?

A

dry matter!! will use dried feed for all further analysis

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13
Q

describe nutrient content before and after dry matter

A

nutrient concentrations are always higher on a dry matter basis

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14
Q

how is crude protein measured in proximate analysis?

A

estimated by measuring nitrogen content of feed multiplied by a factor of 6.25

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15
Q

nitrogen makes up what percent of protein?

A

16%

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16
Q

why is crude protein measure only an estimate?

A

because you are not directly measuring protein, but measuring nitrogen instead; but other feedstuff components contain nitrogen too so not super accurate, just a cheap measure

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17
Q

how is crude fat measured in proximate analysis?

A

extracting fat from a sample with ethyl ether

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18
Q

why is measuring crude fat also only an estimate of the amount of lipid in a feedstuff?

A

because you will also extract all other fats in the sample, including waxes which are not digestible

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19
Q

what does measuring ash in proximate analysis tell you?

A

measures inorganic portion, like minerals

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20
Q

what is used to get ash from a feedstuff sample? describe the process

A

a muffle furnace; heats to 500-600 degrees celsius and burns until all that is left of the sample is that ash

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21
Q

describe the efficacy of ash measurement

A

is a quantitative measure rather than qualitative since it does not tell you which specific minerals are in the feedstuff, just what amount; would need further analysis

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22
Q

what is the most useless of the proximate analyses?

A

crude fiber; not reliable and not very accurate

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23
Q

what does crude fiber measure?

A

the indigestible portion, which is usually fiber

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24
Q

how does measuring crude fiber work?

A

BOIL sample in a weak acid to mimic stomach, then BOIL in a weak base to mimic the small intestine, then filter and see what’s left

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25
Q

what are the 3 issues with the process of measuring crude fiber?

A
  1. the body does not BOIL!!
  2. acids and bases do not DIGEST, ENZYMES do
  3. does not measure microbial digestion
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26
Q

what are 2 methods that can be used to measure fiber other than the crude fiber method?

A
  1. NDF: neutral detergent fiber

2. ADF: acid detergent fiber, performed after NDF

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27
Q

describe the NDF method (3)

A
  1. uses a neutral detergent to solubulize cell contents of feedstuff
  2. leaves hemicellulose, cellulose, and lignin (the fiber portions)
  3. much more accurate than crude fiber
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28
Q

describe the ADF method (3)

A
  1. uses an acid detergent to solubulize hemicellulose
  2. leaves cellulose and lignin
  3. more accurate than even NDF
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29
Q

describe hemicellulose digestibility

A

more digestible than cellulose and lignin

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30
Q

what does the ADF method leave for evaluation?

A

the “true fiber” that the BODY can digest

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31
Q

does measuring fiber take into account microbial digestion?

A

no; microbes can digest all

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32
Q

what is nitrogen-free extract?

A

a calculated value that estimates the available/digestible carbohydrates

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33
Q

what does nitrogen-free extract also include in its measure? why?

A

vitamins; there is no proximate analysis to measure vitamins

34
Q

why does the amount of vitamins indirectly measured in nitrogen free extract not matter?

A

it is such a small percentage, is negligible

35
Q

how is nitrogen-free extract (NFE) calculated?

A

100-(water+CP+CF+EE+ash)

36
Q

how do we estimate the energy content of feeds?

A

Total Digestible Nutrients (TDN)

37
Q

what is TDN?

A

total digestible nutrients; sums all fractions of feeds that are digestible to measure energy

38
Q

how do you calculate TDN?

A

digestible CP + digestible CF + digestible NFE + 2.25(digestible EE)

39
Q

why do you multiply ether extract by 2.25 when calculating TDN?

A

because of the 4, 9, 4 rule: for every 1 gram of caarbohydrate there are 4 kcal, for every 1 gram of fat there are 9 kcal, and for every 1 gram of protein there are 4 kcal; 9/4=2.25, so fat has 2.25 times the amount of kcal as carbs and protein

40
Q

what kind of indication of nutrient content does proximate analysis give?

A

a general indication

41
Q

do methods exist to measure specific indications of nutrient content?

A

yes; they just go beyond proximate analysis and take extra time, work, and resources

42
Q

define a kcal

A

the amount of energy needed to increase 1 gram of water by 1 degree celsius

43
Q

what is gross energy?

A

the amount of heat produced when a feedstuff is completely oxidized

44
Q

is gross energy useful to know about a feedstuff?

A

not really

45
Q

how do you determine the gross energy content of feed?

A

by using a bomb calorimeter

46
Q

what does measuring energy via use of a bomb calorimeter NOT tell us? give an example

A

tells us nothing about how the energy can be used by the animal
ex) if feedstuff is very fibrous, usable energy will be drastically different from gross energy

47
Q

in what nutrient way will animals always try to eat?

A

animals will always try to eat to meet their energy requirements

48
Q

describe the 4 levels of energy partitioning, including what energy is lost to at each level

A
  1. begin with gross energy, but energy is lost to fecal material
  2. what’s left is digestible energy, and some is lost to urine and gases
  3. after that is metabolizable energy, and some of that is lost to heat increment
  4. finally left with net energy, which goes to maintenance first, then production
49
Q

what is digestible energy?

A

the amount of energy digested and absorbed by the animal

50
Q

how do you calculate digestible energy?

A

DE = GE - fecal energy

51
Q

describe the accuracy of digestible energy

A

much more accurate than gross energy, but doesn’t tell if or how the cells are using energy

52
Q

what is metabolizable energy?

A

the amount of energy available for cells of the body to use

53
Q

how do you calculate metabolizable energy?

A

ME = DE - urine energy - gas energy

54
Q

how do you measure metabolizable energy? downside?

A

need specialized rooms with sensors that are very expensive, so we use general values instead

55
Q

what is net energy?

A

the most accurate measure; tells what energy is used by the body for maintenance and production

56
Q

how do you calculate net energy?

A

NE = ME - heat increment

57
Q

what is heat increment?

A

the heat released during metabolism

58
Q

how do you measure heat increment?

A

need another expensive ass room

59
Q

what is net energgy SUPER important for?

A

determining energy requirements in dairy animals

60
Q

what is digestibility?

A

the amount of feed that is ingested and absorbed by the animal

61
Q

what does apparent digestibility NOT take into account?

A
  1. heat/gas losses

2. endogenous products which contain nutrients themselves (enzymes, wastes, old cells)

62
Q

what are the 5 methods of determination of apparent digestibility?

A
  1. total collection in metabolism crate
  2. using collection bags
  3. nylon bags for ruminants
  4. using fecal marker
  5. ileal digestibility
63
Q

what does true digestibility account for?

A

endogenous losses

64
Q

what is used to calculate true digestibility?

A

standard values of endogenous losses for each species

65
Q

describe total collections in metabolism crates (3)

A
  1. animal housed in a crate and fed a known amount of food
  2. ALL feces are collected
  3. nutrient content of both feed and feces is measured;
66
Q

what is the formula to calculate digestible nutrients from total collection in a metabolism crate?

A

(feed nutrient - feces nutrient)/feed nutrient; multiply by 100 to get % digestible nutrient, measure one nutrient at a time

67
Q

describe the total collection method in terms of ease and how long can keep animal in the crate

A

relatively easy method, but can only keep animal in crate for up to 2 days

68
Q

what must you do to the animal before performing total collection in a metabolism crate?

A

have to fast animal beforehand to start fresh

69
Q

describe using collection bags to measure digestibility (3)

A
  1. attach bag to hind end of animal to catch feces
  2. feed animal a known amount of feed
  3. measure nutrient content of feed and feces
    use same calculation as total collection in metabolism crate
70
Q

what is the downside to using a collection bag to measure digestibility?

A

bags aren’t comfortable for any animal; animal may try to remove bag

71
Q

what are the nylon bags used to measure digestibility in ruminants?

A

mesh-like bags to allow microbe access

72
Q

describe the use of nylon bags to measure digestibility in ruminants (3)

A
  1. place a known amount of feed in a nylon bag
  2. place bag in the rumen of animals
  3. remove bag after set amount of time and measure nutrient content of starting and end bag contents; the difference in the two tells digestibility in RUMEN
73
Q

what are the downsides of using nylon bags to measure digestibility in ruminants?

A
  1. requires canulated animals, which are very expensive

2. only measures microbial digestibility, not any digestibility in any other part of the tract

74
Q

what is the super cool advantage of using fecal markers to measure digestibility?

A

don’t have to do total feces collection! only need one sample!

75
Q

describe the process of using a fecal marker to measure digestibility (4)

A
  1. adding an indigestible marker to the feedstuff at a known concentration (ex. stainless steel grit)
  2. collect feces when marker appears and measure marker concentration in feces
  3. measure nutrient concentration in feed and feces
  4. compare marker and nutrient concentration to measure digestibility
76
Q

describe the expected concentration of a fecal marker in the feed versus in the feces

A

concentration of the marker should be higher in the feces, as everything else should have been digested

77
Q

describe ileal digestibility as a way to measure digestibility (3)

A
  1. feed an animal a known amount of feed
  2. collect contents of ileum of small intestine
  3. measure nutrient concentration of feed and ileal content; the difference between the 2 tells what was digested
78
Q

why is ileal digestion a good measure of digestibility?

A

ileum is the end of the site of nutrient absorption (small intestine) so gives a good idea of what all was digested and absorbed without fecal collection

79
Q

what is the downside to measuring ileal digestibility?

A

also requires canulated animals

80
Q

when canulating an animal, what must be done to the organ of interest and why?

A

attach organ of interest to abdominal wall to avoid spillage

Nutrition (19 decks)

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