Evaluation of Feeds III Energy 1 16 23 Evaluation of Feeds III Feed Energy and Partitioning of Energy within an Animal Feed energy o Feed energy is not a nutrient per se but rather a property of nutrients o Nutrients that supply energy include Carbohydrates fiber and starch Lipids Proteins o Feed energy is used by animals for Mechanical work Chemical work Synthesis of enzymes and hormones Maintenance of homeothermy Synthesis of animal products Feed energy o Energy is the most critical attribute to consider regarding nutritional value of feeds o The ability of a feed to supply energy to an animal is of great importance in determining it s relative feed value o Unlike a nutrient feed energy can not be determined chemically but it can be converted to heat which can be measured o The unit used to measure feed energy values is the calorie kcal 1 000 calories Mcal 1 000 kcal 1 2 3 1 Evaluation of Feeds III Energy 1 16 23 Partitioning of feed energy o Partitioning of feed energy refers to the quantification of energy losses associated with the digestion and metabolism of feed vs the net energy available to an animal to support maintenance or productive functions o Energy losses include i fecal ii urine iii methane and iv heat increment Energy partitioning of feed energy by animals Values listed are for Bermudagrass hay Mcal kg DM Gross Energy 4 45 Digestible Energy 2 16 Metabolizable Energy 1 77 Fecal energy losses Urine and CH4 energy losses Heat increment losses Maint Heat increment losses Growth Net energy Maintenance 0 93 Net energy Growth 0 39 Feedstuffs GE kcal g Gross energy GE o Gross energy represents the potential energy of a feed o Gross energy is also referred to as heat of combustion o Gross energy provides limited information on the availability of the feed s potential energy o For example there is very little difference in GE values of feeds e g hay vs corn Starch Cellulose Corn grain Grass hay Corn oil Soybeans whole DM 4 18 4 18 4 40 4 50 9 40 5 40 4 5 6 2 Evaluation of Feeds III Energy 1 16 23 Gross energy How to measure Gross energy is measured as the heat produced upon complete oxidation of a feed to CO2 and H2O in a bomb calorimeter Energy partitioning of feed energy by animals Values listed are for Bermudagrass hay Mcal kg DM Gross Energy 4 45 Digestible Energy 2 16 Metabolizable Energy 1 77 Fecal energy losses Urine and CH4 energy losses Heat increment losses Maint Heat increment losses Growth Net energy Maintenance 0 93 Net energy Growth 0 39 Digestible energy DE o DE Gross energy fecal energy FE o FE represents energy losses due to undigested feed and metabolic fecal material e g undigested microbes o DE is similar in accuracy to TDN because like TDN DE does not account for losses associated with methane urine and heat increment o DE overestimates the useful energy value of roughages relative to grains o Ranges in fecal energy losses Pigs 3 to 20 of GE Horses 10 to 40 of GE Ruminants fed high grain diets 10 to 30 of GE Ruminants fed high roughage diets 40 to 60 of GE 7 8 9 3 Evaluation of Feeds III Energy 1 16 23 Digestible energy How to measure Conventional digestion trial o Collect feed and fecal samples as previously described o To determine DE the gross energy content of feed and fecal samples are measured o DE Feed GE Fecal GE Steer fitted with a fecal collection harness for conducting a digestion trial 10 11 12 Energy partitioning of feed energy by animals Values listed are for Bermudagrass hay Mcal kg DM Gross Energy 4 45 Digestible Energy 2 16 Metabolizable Energy 1 77 Fecal energy losses Urine and CH4 energy losses Heat increment losses Maint Heat increment losses Growth Net energy Maintenance 0 93 Net energy Growth 0 39 Metabolizable energy ME o ME DE urine energy UE gaseous products of digestion GPD o Urine energy is energy lost in the urine due to incomplete oxidation of nitrogenous compounds urea o Ranges in urine energy losses Pigs 2 to 3 of GE Ruminants 3 to 4 of GE o GPD represent energy lost as combustible gases mainly methane during fermentation o Ranges in methane energy losses Pigs 1 to 2 of GE Ruminants on high grain diets 4 to 6 of GE Ruminants on high roughage diets 6 to 12 of GE o Metabolizable energy is more accurate than DE in predicting a feed s useful energy value 4 Evaluation of Feeds III Energy 1 16 23 Metabolizable energy How to measure Urine energy UE o During digestion trials daily urine volume is quantified and gross energy content of urine samples measured using bomb calorimetry Methane energy Indirect respiration calorimetry used to measure CH4 gas produced Also referred to as whole animal calorimetry CH4 energy loss Liters of CH4 produced x 9 4 kcal L ME Feed DE UE CH4 energy losses GreenFeed System Measures CH4 emissions in grazing cattle Cattle carbon cycling vs Fossil fuels Energy partitioning of feed energy by animals Values listed are for Bermudagrass hay Mcal kg DM Gross Energy 4 45 Digestible Energy 2 16 Metabolizable Energy 1 77 Fecal energy losses Urine and CH4 energy losses Heat increment losses Maint Heat increment losses Growth Net energy Maintenance 0 93 Net energy Growth 0 39 13 14 15 5 Evaluation of Feeds III Energy 1 16 23 Net energy NE o NE ME heat increment HI o or NE GE FE UE CH4 HI o NE is the portion of gross energy that is directly available to an animal to perform metabolic functions e g maintenance growth lactation o NE is the most accurate estimate of a feed s effective energy value Heat increment HI 1 Heat of Digestion Fermentation Ingestion of feed e g chewing ruminating Actions of digestive enzymes within the GIT Movement of digesta through the GIT Absorption of nutrients from GIT Actions of microbial fermentation in the GIT 2 Heat of Nutrient Metabolism Heat associated with the metabolic processes of product formation e g muscle synthesis 3 Heat increment Heat of digestion fermentation and nutrient metabolism Represents the inefficient use of ME for maintenance and production Heat increment is only useful only during cold stress Net energy NE 1 NE used to maintain body tissue is referred to as NEm ends up as heat 2 NE used to deposit lean and adipose tissue is referred to as NEg 3 NE used to produce milk is referred to as NEl 4 NE used for fetal growth and development is referred to as NEp 16 17 18 6 Evaluation of Feeds III Energy 1 16 23 Eating activity Diet quality effects on energetic cost of eating in ponies Eating rate g Cost of eating DM min Joule per g DM Feed Wheat straw Poor quality hay