L8: Feed Evaluation 2 Flashcards
_*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)
*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
*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
*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)
Draw flow chart showing energy systems order
*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)
*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
*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
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
*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
*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
What does acid-detergent insoluble (ADIN) nitrogen measure?
- Measures unavailable N for ruminants
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
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
