11/15/20131ENERGY CONCEPTSFUNCTIONS OF ENERGY• Energy = ability to perform work• Mechanical work• Formation of substrates• Active transport• Transfer of genetic information• Maintenance11/15/20132ENERGY – CONTAINING NUTRIENTS• Carbohydrate• Protein• FatBreak Bonds Release Energy• Chemical energy varies inversely with C/H ratio and O and N content• Glucose – 1 atom O per 1 atom C• Glycerol trioleate – 1 atom O per 9.5 atoms CUNITS OF MEASURE• 1 calorie = 4.18 Joules• Amount of heat required to raise temperature of 1 gram water 1oC• More frequently used measurements• 1000 calories = 1 kcal• 1000 kcal = 1 Mcal11/15/20133FORMATION AND USE OF ENERGYANIMAL ENERGY REQUIREMENTS•Maintenance•Production•Growth•Work11/15/20134OVERVIEW OF ENERGY METABOLISMWater Protein Fat CHO Mineral VitaminFeedNutrients to TissuesFecesHeatGas UrineProductive FunctionsMaintenance Growth Work Lactation GestationTHE BASICS…• The “Energy Balance Equation”• Energy In = Energy Out + Energy to Stores• Energy can be neither created nor destroyed• Energy (nutrients) in the body must be used, stored, or excreted11/15/20135ENERGY BALANCE• Positive energy balance• Energy In > Energy Out• Weight gain• Negative energy balance• Energy Out > Energy In• Weight loss• Energy equilibrium• Energy Out = Energy In• Weight maintenanceMEASURING ATP PRODUCTION IS PRETTY DIFFICULT…• Scientists use another method called bomb calorimetry• The principles of calorimetry• Food is completely oxidized (burned) in presence of oxygen• C, H, O and N left• Amount of heat released during explosion is measured11/15/20136CALORIMETRY1 calorie = amount of heat (energy) needed to raise 1 gram of water 1 degree CentigradeBomb calorimeter used to determine calories = Gross EnergySTILL NEED A USEFUL ENERGY VALUE• The problem – values obtained by a bomb calorimeter do not account for digestibility and metabolism in the animal• Fecal energy loss is significant in all animals• Must account for this to accurately determine energy needs and value of a feedstuff• Total Digestible Nutrient (TDN) system attempted to improve energy value by adjusting for digestibility• TDN does not account for other potential losses• Fermentation11/15/20137TOTAL DIGESTIBLE NUTRIENTS (TDN)• Determined by a digestion trial• Calculate the sum of nutrient digestibility• Values lie between DE and ME• 1 kg TDN = 4.4 Mcal DE• Similar disadvantages as DETOTAL DIGESTIBLE NUTRIENTSProximate AnalysisAmt. % Digest. % Digest. Nut.Crude Protein 17 70 11.9Crude Fat 3 85 (2.25) 5.7Crude Fiber 26 60 15.6Ash 10 ------ ------Water 12 ------ ------NFE 32 78 25Total 100 58.211/15/20138OBTAINING USEFUL ENERGY VALUES• Chemical analysis of feeds for energy is of no value• Must take into account utilization by the animal• Most feeds similar gross energy• Values obtained by bomb calorimeter are similar• Only differences due to fat and ash• Other differences exist….• Digestibility • Availability for ATP formationNET ENERGY SYSTEM• Improved on TDN system• Direct application of the First Law of Thermodynamics• Energy can be neither created or destroyed• Energy can be interconverted between different forms• Thermal energy cannot be converted to any other form11/15/20139ENERGY PARTITIONINGGross Energy (GE)Digestible Energy (DE)Metabolizable Energy (ME)Net Energy (NE)Energy LostIn Feces (FE)Energy LostIn Urine and Gases (UE and GPD)Energy LostIn Heat (HI)NEm NEg NElTHE PROBLEM• How well does corn grain meet the net energy needs of a dairy cow? Oat straw?• Our subject: Our test feeds:• What samples do we need to obtain?11/15/201310GROSS ENERGY (GE)• Heat of combustion• Bomb calorimeter• Provides little information on nutrient utilizationFeed GE, kcal/gCorn Grain 4.40Wheat Bran 4.50Grass Hay 4.50Oat Straw 4.50SBM 5.50LSM 5.10NET ENERGY SYSTEMGrossEnergy (GE)Digestible energy (DE)Fecal energy• Undigested feed residues• Metabolic products11/15/201311FECAL ENERGY (FE)• Largest energy loss• Two sources:• Undigested food• Indigestible• Increased rate of passage• Endogenous• Active secretion• Cells slough• Undigested microbes and their metabolitesDIGESTIBLE ENERGY (DE)• Represents “apparent digestibility” of a feedstuff• Losses differ by species• Cattle and sheep• 40-50% for roughages• 20-30% for grains• Horses are 35-40%• Pigs are 20%• Provides some assessment value• Similar to TDN• Major weakness• Overestimates value of high fiber diets• Equine NRC11/15/201312DIGESTIBLE ENERGY (DE)APPARENT DIGESTIBILITYDE = GE – fecal energyGross energy of feedGross energy of feces = fecal energyENERGY VALUE OF SELECTED FEEDSFeed GE DEAlfalfa hayBarley grainCorn grainSoybean mealTimothy hayOat Straw3.894.144.414.694.444.502.513.664.013.632.632.4311/15/201313NET ENERGY SYSTEMDigestibleEnergy (DE)Metabolizableenergy (ME)Urinary energy• N disposalGaseous energy• Gaseous products of fermentationURINARY ENERGY (UE)• Total gross energy in urine• Includes energy from:• Non-utilized and absorbed compounds from food• End products of metabolism• End products of endogenous origin• Loss is relatively stable• Influenced by diet• Excess protein• Urea in mammals• Uric acid in birds• 2-3% of gross energy for pigs• 4-5% of gross energy for cattle11/15/201314GASEOUS ENERGY• Methane (CH4) is primary• Hydrogen, CO2, acetone, ethane and hydrogen sulfide• Greatest gaseous losses in ruminants• 82% of DE• Gaseous losses so small that not considered for ME calculation in man, pigs, dogs and chickens• >95% of DE• H, CO2, acetone, ethane• Can be measured directly or indirectlyMETABOLIZABLE ENERGY (ME)• Greater assessment value than DE• Used by swine and poultry NRC• Used in human nutrition• Can be calculated from DE (rather than directly measured)11/15/201315ME = DE – gas and urine (UE) energyGross energy of gasGross energy of urineENERGY VALUE OF SELECTED FEEDSFeed GE DE MEAlfalfa hayBarley grainCorn grainSoybean mealTimothy hayOat Straw3.894.144.414.694.444.502.513.664.013.632.632.432.033.103.432.982.162.0111/15/201316NET ENERGY SYSTEMMetabolizableEnergy (ME)Net Energy (NE)Heat increment energy (HI)• Heat of digestive fermentations and actions• Heat of metabolismHEAT INCREMENT (HI)• Can represent 25-40% of gross energy