L19: Energy Partitioning Flashcards Preview

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Flashcards in L19: Energy Partitioning Deck (13)
1

Draw energy partitioning flow chart

2

*Describe what factors influence the Gross Energy of a feed

• GE of food depends on degree of oxidation (C+H : O ratio)

• Carbs have similar GE values (roughly 18.4MJ/kg

• Fats much higher (depends on chain length)

• Proteins intermediate

• Measured by heat of combustion 

3

What is DE?

Digestible energy (DE)

• GE feed- GE faeces 

4

What is ME?

Metabolisable energy (ME)

• DE less urine and gas losses

• Urinary energy losses through N containing compounds

• Gas losses in ruminants – mainly methane (8 - 12% of DE depending on feeding level and digestibility)

• In ruminants generally 20% of DE • Less in monogastrics 

5

Which is more important for ruminants:
DE or ME?

For monogastrics?

  • Ruminants ME due to gas loss
  • Monogastrics DE as don't ruminate

6

*Describe factors influencing the heat increment of a feed

Food ingestion results in heat production
• No productive value unless in a cold environment

• Causes of the heat increment:
Eating (chewing, swallowing, saliva) requires energy. (3-6% of ME intake for a ruminant on a fibrous food)

Microbial metabolism (7-8% of ME intake)

Nutrient metabolism
- Amount will vary depending on function (e.g. glucose to ATP vs glucose to glycogen)
- Protein metabolism accounts for about 10% of heat production

Substrate movement against concentration gradients

- ‘ion pumping’ can account for 10% of heat increment

7

What is NE?

Energy available for useful purposes

• maintenance and production

• Maintenance NE mainly used to maintain bodily functions and therefore leaves body as heat

• Production NE either stored (growth) or leaves the body (wool, milk, eggs) 

8

*Discuss factors affecting the efficiency of ME use for maintenance and production 

Overview?

No ME intake – negative energy retention - Animal uses body reserves

When energy retention is zero
- ME intake is sufficient to meet requirement for body maintenance

• Slope of line of retention to intake is a measure of efficiency of ME use. 

- E.g. if 10MJ ME consumed results in 6MJ NE retained, slope is 0.6

• These efficiency values are called ‘k’ values

9

*Discuss factors affecting the efficiency of ME use for maintenance and production

What do the following k values stand for:
Km
Kp
Kf
Kg
Kl
Kc
Kw
Kwool

10

*Discuss factors affecting the efficiency of ME use for maintenance and production

Describe utilisation of ME for maintenance

• Dietary fat and soluble carbs used with high efficiency

• Protein efficiency much lower

• Major energy source for ruminants will be VFA • Used efficiently

• Not as efficiently as glucose though

• Efficiency less in practice as whole foods produce heat loss in digestion and fermentation

11

*Discuss factors affecting the efficiency of ME use for maintenance and production

Describe utilisation of ME for production

• Efficiency depends on whether fat, protein or carbohydrates (e.g. in milk) are being produced

• Efficiency can also be altered by the mix of the ration (associative effects) and the balance of nutrients

12

*Discuss factors affecting the efficiency of ME use for maintenance and production

Describe utilisation of ME for growth

Theoretically this can be high
- E.g.1 Efficiency of synthesis of a triglyceride from acetate and glucose is 0.83

- E.g.2 Efficiency of protein synthesis is 0.85 if all amino acids are present (otherwise synthesising and deaminating will cost)

In practice much lower efficiency due to costs associated with eating and digestion

- Feeding trials have measured efficiency of fat and protein deposition

- Protein much lower as both breakdown and synthesis required

13

*Discuss factors affecting the efficiency of ME use for maintenance and production

Describe utilisation of ME for milk

• Efficiency of lactose synthesis from glucose about 0.96

- but in the cow will largely be synthesised from propionate

• In ruminants experiments have shown kL varies from 0.56-0.66

- Use body reserves to synthesise milk with an efficiency of 0.84

Greater efficiency for kL than for growth due to simpler energy and protein stores in milk