L21: Energy Systems Flashcards
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
increasing
-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) - CURRENT:
-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
km
Kg
Kl
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
DO IT.
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
production)
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
- NEFAs
- 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**
