DETERMINATION OF FEED ENERGY CONCENTRATION PP. 109-120

1. DETERMINATION OF FEED ENERGY CONCENTRATIONPP. 109-120

2. TOTAL DIGESTIBLE NUTRIENTS (TDN) • Traditional system to express digestible energy concentration of feedstuffs • Basis of TDN are physiological fuel values

3. Calculation • Conduct a digestibility trial and determine the apparent digestion coefficient of: • Crude protein • Crude fiber • Nitrogen free extract • Ether extract • Calculate concentration of each digestible nutrient in the diet • Digestible protein (DP), % DM = CP, % DM x CP dig. % • Digestible crude fiber (DCF), % DM = CF, %DM x CF dig. % • Digestible NFE (DNFE), % DM = NFE, %DM x NFE dig. % • Digestible EE (DEE), % DM = EE, %DM x EE dig. % • Calculate TDN • TDN, %DM = %DP + %DCF + %DNFE + (2.25 x %DEE)

4. Equivalence in energy units • 1 lb TDN = 2000 kcal Digestible Energy • 1 kg TDN = 4400 kcal Digestible Energy • Limitations of TDN • Limitations with digestion trials • Errors in chemical analyses • Errors in digestibility trials • Low feed intake increases digestibility • DMI at 3x maintenance reduces TDN by 8% • Underestimates or does not include all energy losses in metabolism • Underestimates energy loss in urine (5%) • Does not include methane gas • End product of rumen fermentation • 3 – 10% of feed energy • Does not include: • Work of digestion • Heat of fermentation • Heat of nutrient metabolism • Overestimates the usable energy value of feeds • Particularly of forages Heat increment

5. CALORIC SYSTEM • Energy units • Calorie (cal) • Amount of heat required to increase the temperature of 1 gm of water from 14.5 to 15.5oC • Kilocalorie (kcal) = 1000 cal • Megacalorie (Mcal) = 1000 kcal = 1,000,000 cal • Caloric system subtracts digestion and metabolic losses from the total energy of a feedstuff

6. CALORIC SYSTEM Gross Energy Fecal Losses Digestible Energy Urine Losses Gaseous Losses Metabolizable Energy Heat Increment Losses Net Energy Heat of Nutrient Metabolism Heat of Fermentation Retained Energy Work of Digestion Maintenance Lactation Stored Energy Growth

7. GROSS ENERGY (GE) • Heat of combustion • Total potential energy for the feedstuff • Measure by bomb calorimeter • Burn until completely oxidized • Measure amount of heat released • Fats > Proteins > Carbohydrates • Average ratio 2.5 - 1.7 - 1.0 • Water and Ash have no energy • GE doesn’t differentiate between availability of energy • Little correlation between GE and usefulness to animal • Corn grain- 4.5 kcal/g • Oat straw- 4.7 kcal/g

8. DIGESTIBLE ENERGY (DE) • Digestible Energy = Gross Energy - Fecal losses • Fecal Losses • Ruminants>Monogastrics • Ruminants- • Can be as great as 60% in low quality forage diets • Monogastrics- • Digestibility of energy increases slightly as body weight increases • Can’t be used to express energy requirements of poultry • Relation to Total Digestible Nutrients • 1 lbs. TDN = 2000 Kcal DE • 1 kg TDN = 4400 Kcal DE

9. METABOLIZABLE ENERGY (ME) • Metabolizable Energy = Digestible Energy – (Combustible Gas + Urinary Energy) • Must be calculated in a neutral growth animal • Zero nitrogen balance • Protein stored or lost from muscle will distort values • Urine (Urea) ~ 5% of GE • Lost as a result of protein metabolism • Ruminants>Monogastrics • Combustible gases • Ruminants >>> Monogastrics • Primarily lost as CH4 ~ 3-10% of GE • Monogastric losses are small and usually ignored ~ 0.1-3.0% of DE • Commonly used in poultry and swine diet formulation • Relation to DE • Ruminants • ME, kcal/kg = DE x 0.82 • Swine • ME, kcal/kg = DE x (1.012 - (0.0019 * Protein%)) • May overestimate energy value of byproduct feedstuffs

10. NET ENERGY (NE) • The amount of energy that is completely useful to the animal for maintenance, lactation, or growth • Net Energy = Metabolizable Energy – heat increment • Heat Increment- increase in heat lost because of the energy costs of digestion and the metabolic processes • Work of Digestion • Activity, Chewing, & GI contractions • As much as 30% of total heat lost in animals (ruminants) • Low quality forage increases work of digestion • Movement and excitement for meal • Heat of fermentation • Heat released by microbes during fermentation • ~ 5-10 % of GE • Low quality forage increases heat of fermentation • Increased lipids decreases heat of fermentation • Heat of Nutrient Metabolism • ~10-30% of GE lost • Inefficient use of nutrients during metabolism • Other oxidative reactions that would not be coupled to ATP production • Heat produced during excretion by the kidney • Heat increment may be: • Contribute to thermal regulation in cold climate • Contribute to heat load in warm climate

11. Relationship to ME • Beef cattle • NE (maintenance)= NEm = 1.37ME – 0.138ME2 + 0.0105ME3 - 1.12 • NE (gain) = NEg = 1.42ME – 0.174ME2 + 0.0122ME3 - 1.65 • Swine • NE = 0.726 x ME + 1.33 x EE + 0.39 x Starch – 0.62 x CP – 0.83 x ADF

12. NEm DETERMINATION • Calorimetry • Animal placed in animal calorimeter • ME intake and heat production measured • NE, Mcal/kg = (ME intake – Heat production)/DMI • Comparative slaughter • Feed group a common diet for two weeks • Slaughter a portion of a group of animals and grind carcass and organs • Determine energy content of the whole body, E1 • Feed several levels of feed for a period of time • Slaughter remainder on animals and grind carcass and organs • Determine energy content of the whole body, E2 • RE = (E2 - E1) • NE, Mcal/kg = RE/DMI • Use of NE for maintenance (NEm), body weight gain (NEg), or lactation (NEl) determined by regression

13. Regression equations • NE is calculated from TDN corrected for intake • NEl , Mcal/kg = 0.0245 x TDN, % - 1.12

14. PARTITIONING OF NET ENERGY FOR MAINTENANCE AND GAIN • NEm = HeE/Im • NEg = NEr/(I – Im)

15. NEmREQUIREMENT • Maintenance requirement • The amount of feed energy needed for: • Basal metabolic activities • Body temperature regulation • Physical activity: • Results in zero gain or loss of energy from the body tissues • Requirements: • Beef cattle • NEm = 0.077 Mcal/EBW0.75 • Dairy cattle • NEm = 0.080 Mcal/EBW0.75 • Vary with weight, breed, age, sex, season, temperature, nutritional status, physiological status • Significance in net energy calculations for growing animals • Must always calculate the amount of feed necessary to maintain an animal before calculating how much feed would remain or be needed to achieve a given level of body weight gain

16. NET ENERGY FOR GAIN (NEg) • Net energy remaining after maintenance requirements are met • Net energy is used less efficiently for gain than for maintenance

17. EFFICIENCY OF NE USE FOR LACTATION Lactation + Growth Energy balance 0 Maintenance _ Low Energy in Diet High

18. Significance of equal efficiency of energy use for maintenance and lactation • Net energy requirements for dairy cows can be expressed with one value • Net energy for lactation, Nel • Energy requirement for lactation considers • Amount of milk produced • Fat percentage of milk produced

19. COMPARISON OF ENERGY FRACTIONS IN DIFFERENT FEEDSTUFFS