Energy systems for growing animals

Question 1

Energy sytems

• what they are
• what they are used for

Answer 1

• Energy = Most important nutrient
• Ration formulated to meet energy requirements
  = Sets of rules relating energy supply to energy requirements.
• Energy systems used to:
  ~ Predict performance for given energy supply.
  ~ Calculate energy supply required for given level of performance

Question 2

simplest energy system 2 components

Answer 2

• Energy requirement
• Energy supply
  Example: An animal growing at 1.0 kg requires 15.0 MJ/day
  NE requirement = 15 MJ/kg NE content of feed = 5.0 MJ/kg
  Quantity required = 15/5 = 3.0 kg/day

Question 3

How does the NE value vary

Answer 3

• Productive process (maintenance vs production + type)
• Diet quality (energy substate supply)
• Level of feeding

Question 4

What are energy systems based on

Answer 4

~ most systems energy supply based on ME
- Energy requirements (NE)
- Energy supply (ME)
- Efficiency of ME utilisation (k)
Example: Feed with ME value of 10.0 MJ/kg, k = 0.5
NE value = 10.0 x 0.5 = 5.0 MJ/kg

Question 5

What is energy required for

Answer 5

Maintenance (ME m)
Growth (ME g)
- Total requirement calculated using a factorial approach:
ME t = ME m + ME g

Question 6

Maintenance

- what vital body processes is energy required for

Answer 6

• Essential muscular activity
• Active transport = end products of digestion absorbed into small intestine and blood, no excretion waste products/nutrient spread round body w/o active transport)
• Protein turnover = protein constantly broken down and resynthesised (40% mointence requirment) heifers fatten before steers = lower protein mass
• Enzyme & hormone synthesis

If animal deprived of food, catabolises body tissue for energy (glycogen, fat, protein). Energy evolved as heat

Question 7

How to measure maintenabce energy requirment

Answer 7

• starve animal for 4 days
• no energy from diet
• require energy for vital processess
• use own body tisse to provide energy
• estimate net energy

Question 8

Growth

• what does ME for growth depend on
• what net energy gain depend on

Answer 8

• Total energy gained (NE g)
• Efficiency of ME utilisation for gain (kg)
• Energy value of the gain (EV g)
• Daily gain (LWG)

Question 9

what does energy value of gain depend on

Answer 9

• Liveweight
• Breed type (mature weight)
• Sex
• Rate of gain

Question 10

what does efficiency of metabolisable energy utilisation

Answer 10

• Diet quality (q)
• Level of feeding
• Productive process (fat vs protein)