lecture quiz 8: proximal analysis Flashcards

1
Q

chemical evaluation

A

use of lab techniques to determine [specific nutrient] (& energy) in a feedstuffs/diet

  • doesn’t tell you anything about bioavailabiilty, digestibility, palatability, etc.
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2
Q

biological evaluation

A

using animals to measure utilization of nutrients from a given feedstuffs/diet

  • cannot assume effects on animals based on chemical composition alone
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3
Q

why is a biological evaluation necessary in addition to chemical evaluation?

A
  1. palatability → if animals won’t eat then nutrient composition is useless
  2. bioavailability
  3. digestion & absorption vs excretion
  4. performance
  5. effect on product quality (e.g. milk, meat color, marbeling, methane production)
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4
Q

first step of chemical evaluation

A

get a representative sample: small sample represents entire composition of feed (avg nutrients animal consumes)

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5
Q

common analytical methods used in chemical analysis of feeds/feedstuffs

A
  1. proximate analysis
  2. van soest detergent fiber analysis
  3. near-infrared spectroscopy (NIRS)
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6
Q

proximate analysis

A
  • most widely used method for chemical analysis of feeds/feedstuffs
    • aka Weende methods/procedures (developed in Weende experiment station in germany)
  • proximate principles = compounds occurring naturally in animal & veg tissues & separatable by analytical methods
  • partitions compounds w/in feed into 6 categories based on chem properties
  • sum of 6 components = 100%
  • moisture, ether extract (crude fat), crude fiber, crude protein, ash, nitrogen-free extract
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7
Q

categories of proximate analysis

A
  1. moisture (water)
  2. crude protein (CP) = true protein + NPN
  3. ether extract (EE = crude fat)
  4. crude fiber (CF) = cell wall fraction (fibrous carbs cellulose, hemicellulose, & lignin)
  5. ash = inorganic compounds/minerals (cannot burn)
  6. nitrogen-free extract (NFE) = ‘non-structural carbohydrates’ (sugars, starches) & vitamins → everything that is left over after other categories
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8
Q

DM made up of

A

organic matter + ash

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9
Q

organic matter can be partitioned into:

A
  1. crude protein
  2. crude fiber
  3. ether extract (crude fat)
  4. N-free extract
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10
Q

proximate analysis: moisture (water)

A
  • all feed has moisture + DM
  • to find water content: figure out DM & subtract from 100
  • total matter = moisture + DM
  • method:
    1. weight original sample
    2. heat sample at 105ºC for 24h to dry
    3. weigh dried sample immediately
  • calculations:
    • % moisture = (weight of water loss)/(weight of original sample) x 100
    • % DM = 100 − % moisture
    • OR % DM = (weight of heated sample)/(original weight) x 100
  • official method = forced-air oven @ 105º & weigh samples before & after
  • alternative methods: drying under vacuum or freeze-drying
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11
Q

sources of error during DM proximal analysis

A

heating can cause loss of volatile compounds that are DM during evaporation (e.g. silages or fermented products) ∴ overestimate moisture (underestimate DM)

  • any time drying & smell = loss of volatile compounds (they are pungent)
  • soln = freeze-drying → keep sensitive compounds (samples drying under vacuum & at low temps ∴ not lost in evaporation)
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12
Q

importance of knowing moisture & DM content

A
  1. proper moisture concentration for storage (too much moisture → mold)
  2. DM give basis to describe quantity of feed consumed to compare nutrients btwn feeds
  3. water is diluent of other feedstuffs → too much water in feed = less of other nutrients (“dilutes” food → e.g. equal weight of canned dog food & kibble: wet has less nutrients than kibble)
  4. moisture level affects economic value of feedstuffs (don’t want to pay for water, want to pay for DM where the nutrients/value are → e.g. don’t want to pay for bones when you’re buying meat)
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13
Q

as-fed basis

A

feed as it would be fed to the animal (including water)

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14
Q

DM basis

A
  • assumes no water is present (100% DM)
  • allows to accurately compare nutrient composition of various feedstuffs
  • formulate diet on DM basis
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15
Q

air-dry basis

A

when feeds are allowed to air dry, most absorb water from envir & eventually equilibrate to ~90% DM (~10% moisture)

  • how feed labels are priced
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16
Q

converting amount as-fed to DM

A

amount of feed (as-fed) x %DM/100

17
Q

converting % as-fed to DM

A

% nutrient (as-fed) ÷ %DM/100

18
Q

converting amount DM to as-fed

A

amount of feed (DM) ÷ %DM/100

19
Q

converting % DM to as-fed

A

% nutrient (DM) x %DM/100

20
Q

DM & as-fed conversion useful rules

A
  1. % of a nutrient on a DM basis will always be higher than it would be on an as-fed basis
  2. amount of nutrient on a DM basis will always be lower than amount of feed on an as-fed basis
21
Q

proximate principles

A

compounds occurring naturally in animal & veg tissues are separatable by analytical methods