L21: Energy Systems Flashcards Preview

ASC273 > L21: Energy Systems > Flashcards

Flashcards in L21: Energy Systems Deck (27)

How do we calculate the energy of a feed?

  • in vitro method
  • formulas (Oddy et al)
  • feeding table


What is the basis for forming a feed ration?

  • knowing energy content of feed
  • knowing the energy requirement of the animal


Animals tend to show a ...... response to increasing energy


-not always for other nutrients


What are energy systems?

  • Relates energy intake of animal to its peformance to predict:
    - peformance of animal on energy intake
    - energy req. for performance
  • Feeds work on ME
  • Reqs work on NR
  • Why?
    -different efficiencies w/ each process Lm, Kg, Kl etc
    How do we convert b/w ME and NE?
    - K values (efficiencies)


*List and describe common ruminant energy systems


  • OLD:
    -Armsby's NE sys
    -Kellner's starch equivalents
    both have problems; NE valoues of same food differed depending on function
    -TDN (total digestible nutrients)
    -ARC system


*List and describe common ruminant energy systems

Describe ARC ME system

  • Current british system
  • Provides estimates of energy reqs of growing, lactating and pregnant sheep/cattle
  • Food energy expressed as ME
  • Animal energy reqs expressed as NE
  • Uses series of equations to predict efficiency
    -based on ME/GE ratio (metabolisibility or qm)
    -assumes constant GE of ruminant feeds


What do we use to predicr animal peformance?

  • Calculate metabolisability (qm of feed)
    - ME of feed / GE of feed (as a proportion)
    - eg. 11 MJME/kgDM (GE = 18.4 MJ/kg DM) = 0.6
  • Calculate k values


What is the calculation for Km (maintenance)?

Km = 0.35qm + 0.503


What is the calculation for Kg (growth)?

Kg = 0.78qm + 0.006


What is the calculation for Kl (lactation)?

Kl = 0.35qm + 0.420


Please look in lecture at calculation diagram



What is the issue with calculating metabolisability for a ration formulation?

Method difficult for ration formulation as we often don’t know the total diet ME

• May know part of it (e.g. roughage) but not the rest (grain content) • Often trial and error qm values until we get a match
• Works on the assumption GE = 18.4 MJ/kg DM

Also may not know how much each feed will contribute to maintenance and production

Energy partitioning

Use kmp (average efficiency with which ME used for maintenance and


Kmp = (NEm+NEp)/(NEm/km+ NEp/kp)


What is the current Australian energy system? (ruminant)

  • SCA system (Australian Standing Committee on Agriculture)
  • Includes modications for grazing animals
  • Different Kg for forage diets (incl. tropical forages)
  • Includes Kwool
  • 10% ME for production is added to maintenance when feeding above maintenance level
    -feeding for production


Describe the NRC system (ruminants)

  • National Research Council USA
  • NE sys for beef/dairy
  • Foods given in NE values for both maintenance and gain
  • ***Under predicts NE compared to ARC system


Why do energy systems tend to be more accurate for dairy cows?

  • less variability in diet
  • milk fairly consistent
  • Aus sys appears most accurate
  • don't need to put on weight


Why do monogastric energy systems tend to be simpler?

  • Less variability in food energy
  • Efficiency of ME use (Km, Kg etc) less variable


What are the two monogastric energy systems? (horse)

  • NRC (USA) DE system
    -little diff in equine DE & ME due to digestive sys
    -DE is what seperates feed e values most
    -maintenance is calculated (Km)
    -preg, growth, lact, work are multiples of maintenance
  • INRA (France) system
    -Based on NE
    -relationships b/w NE and DE much morr variable, so not as accurate


Equations were developed to predict ME of feeds for different animals based on:

  • fibre content
  • digestibility
  • protein content
  • fat content
  • starch


Energy requirements are maintenance plus:

  • growth
  • lactation
  • pregnancy
  • work
  • pelage growth


What is meant by maintenance?

  • body compositition does not chnage
  • produces no product
  • not in work


What is meant  by maintenance requirement?

  • quantity req. for no net gain or loss of nutrients
  • steady state


What is basal metabolism?

  • Energy expended (heat) for a fasting animal w/ no activity
  • influenced by age/sex
  • no energy input (feed)
  • animals offered feed will produce extra heat


Briefly describe factors to be considered when estimating energy requirements

describe maintenance energy

• Amount required for zero energy equilibrium (balance)

• Calculate from fasting metabolism allowing for:
- exercise
- Environment

• level of feeding will affect it
- Increase feeding increases efficiency for maintenance

• Age affects energy requirement for maintenance - Development
- Young = more
- Old = less


Briefly describe factors to be considered when estimating energy requirements

describe energy for growth

• Requirements vary with age
- Young = rapid growth
- Old = Storage as fat

• NE in fat higher than in muscle

• Younger animals lay down more muscle than fat
- less energy/kg liveweight gain
- Older animal have greater energy storage / kg BW (FAT!!!)

• Depends on physiological state
• In horses also depends on whether in training


Briefly describe factors to be considered when estimating energy requirements

 describe energy for lactation

• Greatest energy requirement
• May not be able to eat enough to meet energy demands:

- fat reserves
- Concentrates

• After parturition
- milk yield increases
- protein and minerals decrease

• Energy requirement calculated days post-partum or based on yield

- E.g. mare. First 3 months vs later
- (first 3 months highest production)


Briefly describe factors to be considered when estimating energy requirements

 describe energy for work (horses)

• Difficult to quantify requirement as may be influenced by:
- horse condition
- climate
- rider characteristics
- ration composition

• NRC categorise requirements on general workload
- Light
- Moderate
- Intense

• Other equations available based on workload (km x kg) and speed


Briefly describe factors to be considered when estimating energy requirements

 describe environmental effects

• Efficiency with which ME will be used by animals will be affected by:

- temperature
- wind
- precipitation
- humidity
- heat radiation