Energy Systems for Feedstuffs Energy is the potential to do work

Calorie (c) Kilocalorie (kcal) Joule (J) Total Digestible Nutrients (TDN) Gross energy (GE) Digestible energy (DE) Net Energy (NE) Metabolizable Energy (ME)

Definitions –Calorie (cal) Amount of heat required to increase the temperature of 1 g of water from 14.5 to 15.5 o C –Kilocalorie (kcal) = 1000 cal –Megacalorie (Mcal) = 1000 kcal = 1,000,000 cal

Determine Feed Energy Value Total Digestible Nutrients (TDN) Partitioning of Feedstuff Energy Roughage / Concentrate Ratio

TOTAL DIGESTIBLE NUTRIENTS (TDN) Traditional system to express digestible energy concentration of feedstuffs Basis of TDN are physiological fuel values NutrientHeat of combustion, kcal/g Heat of combustion of metabolic products, kcal/g Nutrient absorption, % Physiological fuel value, kcal/g Carbohydrates Fats Protein

Determining TDN –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 –Using all Dry Matter Basis Digestible protein (DP) = CP x CP dig. % Digestible crude fiber (DCF) = CF x CF dig. % Digestible NFE (DNFE) = NFE x NFE dig. % Digestible EE (DEE) = EE x EE dig. % x 2.25 –Calculate TDN TDN, %DM = %DP + %DCF + %DNFE + (2.25 x %DEE) Expressed as a % of the ration OR in units of weight (Lb, kg, etc…) Conversion: 1 Lb TDN = 2,000 Kcal digestible energy 1 Kg TDN = Kcal digestible energy

Limitations of TDN –Limitations associated with digestion trials Errors in chemical analyses Errors in sample collections –Low feed intake increases digestibility –DMI at 3x maintenance reduces TDN by 8% –Does not include all energy losses in metabolism Does not include urine losses Does not include methane gas losses –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

Energy Partitioning Gross Energy (GE) Digestible Energy (DE) Metabolizable Energy (ME) Net Energy (NE) Production (NEp)Maintenance (NEm) Fecal energy loss (FE) Urine (UE) and gas products of digestion (GPD) Heat Increment (HI) Fermentation Digestion Metabolism

GROSS ENERGY (GE) Total potential energy of the feedstuff Measure by bomb calorimeter –Burn until completely oxidized –Measure amount of heat released Fats > Proteins > Carbohydrates –Average ratio 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

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 Cannot be used to express energy requirements of poultry (or reptiles) Relation to Total Digestible Nutrients –1 lbs. TDN = 2000 Kcal DE –1 kg TDN = 4400 Kcal DE DIGESTIBLE ENERGY (DE)

METABOLIZABLE ENERGY (ME) ME = DE – (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 CH 4 ~ 3-10% of GE –Monogastric losses are small and usually ignored ~ % of DE

Metabolizable Energy (ME) cont Commonly used in poultry, swine, companion animal formulations Relation to DE –Ruminants ME, kcal/kg = DE x 0.82 –Swine ME, kcal/kg = DE x ( ( * Protein%)) May overestimate energy value of byproduct feedstuffs –Dogs ME (kcal) = DE – (1.04 x g protein) Works best for industry’s highly digestible diets –Cats ME (kcal) = DE – (0.77 x g protein)

NET ENERGY (NE) The amount of energy that is completely useful to the animal for maintenance, lactation, or growth NE = ME – HI –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 –Heat increment: Contributes to thermal regulation in cold climate Contributes to heat load in warm climate

NE m REQUIREMENT Maintenance requirement (zero gain or loss of energy from body tissues) –The amount of feed energy needed for: Basal metabolic activities Body temperature regulation Physical activity: Requirements: –Beef cattle NE m = Mcal/EBW 0.75 –Dairy cattle NE m = Mcal/EBW 0.75 –Varies 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

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 on whole body (E 1 ) –Feed several levels of feed for a period of time –Slaughter remainder on animals and grind carcass and organs – determine energy on whole body (E 2 ) –Retained Energy (RE) = (E 2 - E 1 ) –NE, Mcal/kg = RE/DMI (assumes a linear relationship) –Use of NE for maintenance (NEm), body weight gain (NEg), or lactation (NE l ) determined by regression

Relationship to ME Beef cattle (based on comparative slaughter) NE (maintenance)= NEm = 1.37ME – 0.138ME ME NE (gain) = NEg = 1.42ME – 0.174ME ME Swine NE = x ME x EE x Starch – 0.62 x CP – 0.83 x ADF

EFFICIENCY OF NE USE FOR LACTATION Low Energy in DietHigh Maintenance Lactation Growth Energy balance 0 _ +

NET ENERGY FOR GAIN (NE g ) Net energy remaining after maintenance requirements are met Net energy is used less efficiently for gain than for maintenance

EFFICIENCY OF NE USE FOR LACTATION Low Energy in DietHigh Maintenance Lactation Growth Energy balance 0 _ +

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, Ne l –Energy requirement for lactation considers Amount of milk produced Fat percentage of milk produced

COMPARISON OF ENERGY FRACTIONS IN DIFFERENT FEEDSTUFFS Corn grain kcal/g Alfalfa Hay (midbloom) kcal/g Oat Straw kcal/g Gross Energy Digest. Energy Metab. Energy NEm NEg

Energy in Beef Nutrition –Predict weight gain –Estimate intake for desired weight gain –This week in lab: NE requirements: Table 2-3 & 2-4, p 105 – 106 NE content: Table 2-5, p