L6: Feed Evaluation Flashcards Preview

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Flashcards in L6: Feed Evaluation Deck (15)
1

*Understand how feed can be tested for dry matter, organic matter, fat content, protein content, and any limitations in the approaches

Describe dry matter testing

  • Determined by drying a known amount for 16h and reweighing
  • All other feed parameters expressed on a dry matter basis
  • varies from 20% to 90%

2

*Understand how feed can be tested for dry matter, organic matter, fat content, protein content, and any limitations in the approaches

Describe organic matter testing

  • Determines ash/mineral content of feed
  • Determined by burning combustible material off
  • Difference b/w DM and IM is organic matter
  • High values indicate contaminaion
  • Destroys sample, not reusable

3

What analysis do we use to determine crude fibre? Explain.

  • Proximate (Weende) analysis
  • Attempts to partition feed into 6 categories:
    -Moisture (DM)
    -Ash (inorganic)
    -Crude protein (N)
    -Crude fibre (acid/alkaline digestion)
    -Crude lipid (ether extract)
    -N-free extract (digestible CHD)
  • Has many faults, not very accurate
     

4

*Understand how feed can be tested for dry matter, organic matter, fat content, protein content, and any limitations in the approaches

Describe crude protein testing

  • Determine nitrogen then x 6.25
  • Feed digested in conc. H2SO4. Yields N
  • NaOH added once cool
  • Mix titrated against acid to determine N in feed
  • Crude protein contains both:
    -true protein (aa)
    -non-protein nitrogen (urea etc)

5

*Understand how feed can be tested for dry matter, organic matter, fat content, protein content, and any limitations in the approaches

Describe ether extraction

  • Fat content of feed
  • Components extracted include true fats, waxes, organic acids, alcohols, pigments, fat soluble vitamins
  • estimates proportion of feed that is high e value
  • Food is continuously extracted w/ petrolium ether for a defined period, the residue after evaporating solvent is ether extract

6

Describe nitrogen-free extraction

  • Diff. b/w original sample weight and the sum of:
    -water
    -ash
    -ether extract
    -crude fibre
    -crude protein
  • Contains primarily soluble CHD such as sugars and starch
  • Useful for estimating soluble CHD  fraction of grains

7

*Describe the various approaches to measuring digestibility

Describe Neutral detergent fibre (NDF)  testing

  • Determines monogastric indigestible cell wall structure (non-ruminant crude fibre)
  • samples boiled in ND solution to remove cell wall contents
  • Residue contains structural components
    -cellulose, hemicellulose, lignin
    -non-digestible in MG
    -partially in R

8

*Describe the various approaches to measuring digestibility

Describe Acid detergent fibre (ADF) testing

  • Good indicator of digestibility
  • Sample boiled in AD solution
    -removes cell wall contents
  • Residue contains cellulose and lignin
    -Cellulose partially digestible in R
    -Lignin non-digetsible
  • NDF - ADF = hemicellulose
    -ID in M
    -PD in R

9

*Describe the various approaches to measuring digestibility

Describe digestibility

  • Proportion of foodstuffs not excreted in faeces and assumed to be used by the animal
  • Can be expressed for whole feed or individual nutrients
    - (amount in feed - amount in faeces) / amount in feed

10

*Describe the various approaches to measuring digestibility

Describe in vivo digestibility

  • difference b/w dry feed offered and faeces excreted as a % of dry feed offered
  • Animals confined or fitted with faecal collection bags
  • Feed consumed/faeces excreted recorded over several days
  • BEST FORM OF DETERMINING DIGESTIBILITY
  • But expenno

11

*Describe the various approaches to measuring digestibility

Describe in vitro digestibility testing

  • Ruminants
    -incubate sample in strained rumen fluid for 2 days, then 2 days in pepsin
    -residue left assumed ID
  • Horses
    -use strained caecal fluid, though can use strained faeces
  • Pepsin/cellulase (synthetic) technique also used (animal ethics)

12

*Describe the various approaches to measuring digestibility

Describe in sacco digestibility testing

  • Nylon bag technique
  • Sealed bags containing feed incubated in rumen of fistulaed animals
  • Useful for time studies

13

*Describe the various approaches to measuring digestibility

Describe digestibility testing using an indicator

  • Use indigestible marker
    -Cr, Yb, Si, alkane waves
  • Measure concentration of indicator in feed and faeces

14

*Describe animal and feed factors affecting digestibility

Feed factors?

  • FOOD COMPOSITION
    -amount of fibrous CHD
  • RATION COMPOSITION
    -composition of other feeds fed
  • PREPARATION
    -chaffing, grinding, crushing
    -alter SA of breaks fibrous hull
    -cooking can alter chemistry

15

*Describe animal and feed factors affecting digestibility

Animal factors?

  • ANIMALS
    -ruminant vs monogastric
    -animals w/in species
  • FEEDING LEVEL
    -more food - faster rate of passage - less digestion?
  • PREVIOUS FEEDING
    -takes time for microbial popn to adjust to new feed