L6: Feed Evaluation

Question 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

Answer 1

• 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%

Question 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

Answer 2

• 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

Question 3

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

Answer 3

• 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

Question 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

Answer 4

• 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)

Question 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

Answer 5

• 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

Question 6

Describe nitrogen-free extraction

Answer 6

• 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

Question 7

*Describe the various approaches to measuring digestibility

Describe Neutral detergent fibre (NDF) testing

Answer 7

• 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

Question 8

*Describe the various approaches to measuring digestibility

Describe Acid detergent fibre (ADF) testing

Answer 8

• 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

Question 9

*Describe the various approaches to measuring digestibility

Describe digestibility

Answer 9

• 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

Question 10

*Describe the various approaches to measuring digestibility

Describe in vivo digestibility

Answer 10

• 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

Question 11

*Describe the various approaches to measuring digestibility

Describe in vitro digestibility testing

Answer 11

• 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)

Question 12

*Describe the various approaches to measuring digestibility

Describe in sacco digestibility testing

Answer 12

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

Question 13

_*Describe the various approaches to measuring digestibility_

Describe digestibility testing using an indicator

Answer 13

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

Question 14

_*Describe animal and feed factors affecting digestibility_

Feed factors?

Answer 14

• 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

Question 15

*Describe animal and feed factors affecting digestibility

Animal factors?

Answer 15

• 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