L6: Feed Evaluation Flashcards
_*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%
*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
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
*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)
_*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
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
*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
*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
*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
*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
*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)
*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
_*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
_*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
*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
