L19: Energy Partitioning Flashcards
Draw energy partitioning flow chart
*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
What is DE?
Digestible energy (DE)
• GE feed- GE faeces
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
Which is more important for ruminants:
DE or ME?
For monogastrics?
- Ruminants ME due to gas loss
- Monogastrics DE as don’t ruminate
*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
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)
*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
*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
*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
*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
*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
*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
