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Flashcards in L8: Feed Evaluation 2 Deck (14)
1

*Define what is meant by the terms gross, digestible. metabolisable and net energy

What is gross energy?
How do we measure it?

  • Total amount of energy in feed (megajoules)
  • Measure heat of combustion in bomb calorimeter
  • Most feeds have  GE of about 18MJ/kg DM
  • GE digestibility =
    GE in feed (intake) - GE in faeces (output)
    /
    Ge in feed (intake)

2

*Define what is meant by the terms gross, digestible, metabolisable and net energy

What is digestible energy?

  • DE = GE of feed - GE of faeces
  • Energy absorbed by animal (has gone through digestive process)
  • Often used as a measure of energy supply for pigs and horses, but not ruminants
     

3

*Define what is meant by the terms gross, digestible, metabolisable and net energy

What is metabolisable energy?
 

  • Energy that is available for use by animal; some metabolic heat produced
  • Variable and depends on feed type and species
  • Approx. 19% of e digested in ruminants is lost in urine and faeces
  • ME =
    GE of feed - (GE faeces + GE urine + GE gas)
  • Requires respiration chambers to be measured

4

*Define what is meant by the terms gross, digestible, metabolisable and net energy

What is net energy?

  • Energy gained by the animal from the diet
    -used for maintenance, stored as live weight
  • NE =
    ME - heat energy lost (lost in faeces, urine, methane)

5

Draw flow chart showing energy systems order

6

*Define heat increment, and how heat production can be measured directly and indirectly

Define heat increment

How do we measure? (overview)

  • Energy loss as heat
  • Measure heat produced above fasting metabolism
  • Fast animal to gain basal metabolism
  • Increase is the heat increment of the feed (heat energy)
  • Calculated using an animal calorimeter or indirectly from respiratory exchange (O2, CO2, N2)

7

*Define heat increment, and how heat production can be measured directly and indirectly

How do we measure heat production using direct calormitery?

  • Animals don't store heat
    -safe assumption quantity of heat lost = quantity of heat produced
  • Airtight, insulated chamber
    -evaporative losses measured as differences in air moisture
    -sensible heat losses through chamber wall
  • Increase in heat production / increase in ME intake = heat increment

8

*Define heat increment, and how heat production can be measured directly and indirectly

How do we measure heat production using indirect calormitery?

  • Heat produced from oxidation of CHD, fats and protein
  • Need to know how much O2 used to oxidise each component
  • Respiratory Quotient (RQ)
    -ratio b/w CO2 production and O2 consumed
    -used to calculate proportions of fat and CHD oxidised
  • Protein oxidised estimated by urinary N

9

List the techniques available for mineral, vitamin, nonstructural CHD, amino acid and fatty acid analyses

Techniques for starch and sugars? (CHD)

  • Sugars colorimetrically after digestion
  • Starch after hydrolysis and polarimetric analysis

10

*List the techniques available for mineral, vitamin, nonstructural CHD, amino acid and fatty acid analyses

Techniques for minerals?

  • Ash measured by:
    -atomic absorption spectroscopy (radiation)
    -flame emission spectroscopy (burn)
    -inductively coupled plasma emission spectroscopy (ICP) -acid digest
  • Indicates quantity of mineral present not how much available

11

*List the techniques available for mineral, vitamin, nonstructural CHD, amino acid and fatty acid analyses

Techniques for amino acids, fatty acids and fat soluble vitamins?
 

  • Chromotographic separation via GLC or HPLC after proteins or fats are hydrolysed or extracted

12

What does acid-detergent insoluble (ADIN) nitrogen measure?

  • Measures unavailable N for ruminants

13

What is NIRS? 

  • Near Infrared Reflectance Spectroscopy
  • Uses infrared light rays to measue reflectance of a sample
  • Requires large calibration set for which data is known
  • Quick, non-destructuve, cheap

14

What is pXRF?

  • Portable X-ray Fluorescence Spectroscopy
  • Uses short wavelength x-rays to excite sample material
  • Generates characteristic elemental emissions proportional to the [ ] of element present in ground faecal material
  • Minimal sample prep
  • Requires moderate calibration set
  • Portable
  • Reduce costs, analysis duration and error