Energy partitioning

Question 1

What is GE?

Answer 1

gross energy

Question 2

what does gross energy (GE) depend on? What is it measured by?

Answer 2

degree of oxidation (C+H:O ratio)

measured by heat of combustion

Question 3

GE of carbs, fats & proteins…?

Answer 3

carbs - similar GE values
fats - much higher (depends on chain length)
proteins - intermediate

Question 4

Some typical GE values of feeds…?

Answer 4

glucose/cellulose => ~16 & 17MJ/kg dry matter

Maize/oat/hay => ~18.5 - 19.5MJ/kg dry matter

Question 5

What is DE?

Answer 5

digestible energy (GE feed - GE faeces)

Question 6

What is ME?

Answer 6

metabolisable energy (DE - urine & gas losses)

Question 7

Urine & gas losses of metabolisable energy (ME)…?

Answer 7

• urinary energy losses thru N containing compounds
• gas losses (ruminants) - mainly methane (11-13% of DE)
  In ruminants generally 20% of DE
  Less in monogastrics

Question 8

Describe ‘heat increment’…? Give 3 examples of factors contributing to heat increment.

Answer 8

Food ingestion -> heat production
Causes:
- Eating (chewing, saliva, swallowing) requires energy (3-6% of ME ruminant eating fibrous food)
- Microbial metabolism (7-8% of ME intake)
- Substrate movement against [ ] gradients (eg. ion pumping up to 10% heat increment)

Question 9

Define NE…? Include its role in maintenance & production in the body.

Answer 9

Net energy - energy available for useful purposes

• maintenance NE -> maintains bodily functions & thus leaves as heat
• Production NE is either stored (for growth) or leaves the body (wool, milk, eggs)

Question 10

Metabolisable energy (ME) utilisation, energy retention & ‘k’ value…?

Answer 10

no ME intake = -ve energy retention = animal uses body reserves
When energy retention is 0 -> ME intake is sufficient to meet requirement for body maintenance
Slope of retention to intake (slide 12) is a measure of efficiency of ME use denoted by a ‘k’. Thus ‘k’ value is the efficiency of utilisation of ME
Equation: ‘k’ value = energy retained (+ve or -ve) / xMJ ME consumed
eg. 10MJ ME consumed & 6MJ ME retained, slope is 0.6 (k value)

Question 11

Substrates for utilisation of ME for maintenance…?

Answer 11

dietary fat & soluble carbs used with high efficiency

protein - much lower

Question 12

Major energy source in ruminants & ME for maintenance…?

Answer 12

VFAs - used efficiently but less so than glucose

also efficiency in practice is less as whole foods -> heat loss in digestion & fermentation

Question 13

ME use for production…? Efficiency…?

Answer 13

Efficiency depends on whether fat, protein or carbs are being produced. Can be altered by the mix of ration (associative effects) and balance of nutrients

Question 14

ME utilisation for growth…?

Answer 14

Theoretically can be high, but in practice -> lower due to costs associated with eating & digestion
Protein efficiency much lower than fat as both breakdown & synthesis required

Question 15

Why are ‘k’ values in highly digestible feeds (cereal grains) higher in monogastrics than ruminants?

Answer 15

Ruminants have relatively lower ME values due to more energy losses including methane during digestion. Also increased heat losses from digestion & fermentation. ie. greater heat increment???
check this answer…

Question 16

Utilisation of ME for milk…? Lactose synthesis from glucose…? Efficiency of lactation k value

Answer 16

efficiency of lactose synthesis from glucose ~ 0.96
in ruminant exp. lactation k value => 0.56 - 0.66
cows used reserves to synthesise milk with efficiency of 0.84
Greater efficiency for k(l) than growth due to simpler energy & protein stores in milk