Understanding Energy Metrics in Animal Nutrition: Gross, Digestible, Metabolizable, and Net Energy

1. ENERGY 2 Systems TDN Calories

2. GROSS ENERGY

3. GROSS ENERGY Feces

4. GROSS ENERGY Feces DIGESTIBLE ENERGY

5. GROSS ENERGY Feces DIGESTIBLE ENERGY Urine & Gas

6. GROSS ENERGY Feces DIGESTIBLE ENERGY Urine & Gas METABOLIZABLE ENERGY

7. GROSS ENERGY Feces DIGESTIBLE ENERGY Urine & Gas METABOLIZABLE ENERGY Heat increment

8. GROSS ENERGY Feces DIGESTIBLE ENERGY Urine & Gas METABOLIZABLE ENERGY Heat increment NET ENERGY

9. GROSS ENERGY Feces DIGESTIBLE ENERGY Urine & Gas METABOLIZABLE ENERGY Heat increment NET ENERGY Maintenance Gain Reproduction Milk Production

10. Gross Energy includes all the energy in a feed. • It is not all available to the animal • It is determined by how much heat is liberated upon combustion. • Digestible Energy is how much energy does not end up in the feces. • Therefore it was absorbed. • It is not all used by the animal, some is lost. • Metabolizable Energy is what is left after accounting for energy in feces, urine and gasses. • It is still not all available for the animal to use.

11. Net Energy • Is what is left after accounting for losses to feces, urine & gasses and heat increment. • Heat increment is energy lost in fermentation and in metabolic processes. • Net Energy is available for the animal to use. • It is not used with the same efficiency for all processes.

12. Net Energy is always used most efficiently for maintenance. • Milk production is almost as efficient as maintenance. • Gain (growth and fattening) is less efficient.

13. Different uses for energy require different values be used for the energy content of feeds for each purpose. • Maintenance needs must always be met first • This complicates ration balancing.

14. GROSS ENERGY Feces DIGESTIBLE ENERGY Urine & Gas METABOLIZABLE ENERGY Heat increment NET ENERGY Maintenance Gain Reproduction Milk Production

15. Determining Caloric Energy • Use Paar Adiabatic Bomb Calorimeter

16. Steps in determining calories • Prepare sample (grind, pellet, place in bomb) • Wire bomb and charge with Oxygen • Place in calorimeter in known amount of H2O • Measure initial temperature • Ignite • Measure final temperature

17. Calculations • 1 calorie = energy to raise 1 g H2O 1° C • 1000 cal = 1 Kcal • (In humans 1 Calorie = 1 Kcal, animal nutritionists don’t use Calorie vs calorie) • Temp rise X g H2O = calories in sample • Cal in sample X amount of feed = Cal in feed • same for feces

18. Calculate the total calories (or Kcal) (per day) eaten and excreted (in feces, urine). • Calculate DE, ME, Net E (must know the endogenous contribution in Kcal/Kg and % • For Kcal/Kg divide the Kcal of interest by Kg consumed • For %, divide the Kcal of interest by Kcal of feed consumed (times 100).

19. TDN • Total Digestible Nutrients • Forget that, I consider it a misnomer • It is really: • An ENERGY INDEX on a carbohydrate equivalent basis • Calculated from proximate analysis

20. Calculating TDN • % CP X Digestibility = x • % EE X 2.25 X Digestibility = x • % CF X Digestibility = x • % NFE X Digestibility = x • ------ • SUM = TDN TDN

21. Example • Water 12 • Nitrogen 2 • Ether Extract 4 • Crude Fiber 10 • Ash 2 • NFE

22. Example • Water 12 • Nitrogen 2 (2*6.25) 12.5 • Ether Extract 4 • Crude Fiber 10 • Ash 2 • NFE

23. Example • Water 12 • Nitrogen 2 (2*6.25) 12.5 • Ether Extract 4 • Crude Fiber 10 • Ash 2 • NFE 59.5

24. Example digestibility • Water 12 • Nitrogen 2 (2*6.25) 12.5 .80 • Ether Extract 4 .75 • Crude Fiber 10 .40 • Ash 2 • NFE 59.5 .80

25. Example digestibility • Water 12 • Nitrogen 2 (2*6.25) 12.5 .80 = 10 • Ether Extract 4 * 2.25 * .75 =6.75 • Crude Fiber 10 .40 = 4 • Ash 2 • NFE 59.5 .80 = 47.6 • ----------------- • TOTAL (TDN) 68.35