1.6 Comparative Nutrition - Energy

Question 1

What is energy?

Answer 1

• Not a nutrient, rather derived from specific nutrients (organic compounds); protein, lipids, CHOs, VFAs
• Energy yield differs btw nutrients
• NO energy from minerals and water (bc no organic bonds)

Question 2

What 4 things should energy systems provide?

Answer 2

1. Accurate energy estimate
2. Simple application
3. Additivity of energy values
4. Easy determination of energy values

Question 3

What is meant by additivity?

Answer 3

The sum of energy from ingredients = energy in diet

Question 4

Gross Energy (GE)

Answer 4

• Easy to determine
• Combustion in adiabatic bomb calorimeter
• Basis for other energy systems
• Meaningless for pig/poultry production
• No accounting for any losses during digestion and metabolism

Question 5

Digestible Energy (DE)

Answer 5

• DE = GE - Fecal energy
• Usable measure for dietary energy
• Easy to determine
• No accounting for: urine energy loss, combustible gases, losses in metabolism
• Overestimates energy from protein and fiber; not accounting for cost of getting rid of protein waste and energy lost in the form of gas and microbial fermentation

Question 6

Metabolizable Energy

Answer 6

ME = DE - urinary energy - gaseous energy
- accounts for some energy losses in metabolism
- still comparatively easy to determine
- no accounting for efficiency of nutrient utilization

Question 7

In birds, excreta contains both urine and feces. How is ME usually formulated?

Answer 7

On a nitrogen corrected apparent ME (AMEn) basis
- the assumption being ME is more precise if corrected for N excretion (not entirely true) which is excreted as uric acid that both contains and requires energy

Question 8

Net Energy

Answer 8

NE = ME - HI
- energy actually used for production and maintenance
- most accurate way to express dietary energy
- difficult to determine accurately
- same feed will have different NE for different animals, performance levels
- indirect calorimetry

Question 9

Heat increment

Answer 9

HI: heat lost during digestion and metabolism of nutrients; can be thought of as retained energy + fasting heat production

Question 10

How does the expression of energy utilization differ between DE/ME and NE?

Answer 10

• DE or ME express potential amount of energy for animal
• NE expresses actual energy; includes efficiency of energy utilization

Question 11

How does energy utilization (NE) of pigs differ among nutrients?

Answer 11

Protein: 40-60%
Starch and lipids: 74%-90%
Fiber: 50%

Question 12

What are NE prediction equations used for?

Answer 12

To generate NE values used for feed formulation

Question 13

Energy systems used for poultry

Answer 13

• Little added accuracy of diet formulation for NE vs AMEn
• Much higher cost of NE determination than AMEn
• Low $ incentive to switch
• Value of NE increases with increased use of plant coproducts/byproducts

Question 14

Energy systems used for pigs

Answer 14

• NE better predictor of pig performance than DE or ME
• Higher fibre content of pig feeds
• More hindgut fermentation

Question 15

Between energy systems, what nutrient has the greatest loss of energy?

Answer 15

CP > > EE > Starch

Why decreased ranking of soybean meal with NE?
- because it is a high protein source!