These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute. Lecture 5 Outline of Last Lecture II. Energy & Bioenergetics a. Energy i. Gross Energy (GE) ii. Digestible Energy (DE) iii. Metabolizable Energy (ME) iv. Net Energy (NE) v. Heat Increment (HI vi. Heat of Fermentation (HF) Consequences of Heat Increment and Heat of Fermentation Outline of Current Lecture III. Energy & Bioenergetics Continued a. Practical use of “Energy” data b. Expression of beef cattle requirements c. Maintenance d. Partition of Dietary Energy e. Energy “Efficiency” f. Energy equivalents of food & alcohol g. Indirect measurement of metabolic energy h. Energy from Food components i. Energy in feed Current Lecture Practical use of “Energy” data… - GE is of little direct value for evaluating feedstuffs - DE (and TDN) are sometimes used with swine and horses o Total Digestible Nitrogen (TDN) - ME values are used for poultry - DE, TDN, or ME are typically given for sheep and goats For beef cattle, requirements or feed values are expressed as… AN_SCI 3212 1st Edition- Net energy for maintenance (NEm) o NEm = 77 kcal x BW0.75 Energy needs for pregnancy & lactation are also expressed NEm Net energy for gain (NEg) is less efficient than NEm, but most computer formulation programs take this into account in the subsequent calculation Equation is based on numerous calorimetric studies Maintenance In the context of animal nutrition this term refers to a condition in which a non-productive animal neither gains nor loses body energy reserves Studies in beef cattle suggest that 65-70% of the ME needed for normal production is used to meet maintenance needs Energy required for maintenance is mostly needed to produce ATP Maintenance energy (ME) is used for blood circulation, kidney and liver functions, respiration, protein and lipid biosynthesis and turn over, ion transport Partition of Dietary Energy - Gross Energy (GE) → Fecal Energy & Digestible Energy (DE) - Digestible Energy (DE) → Gaseous and Urinary Energy & Metabolizable Energy (ME) - Metabolizable Energy (ME) → Heat Increment + Heat of Fermentation & Net Energy (NE) - Net Energy (NE) → NEmaintenance¬ & NEgain Energy “Efficiency” Efficiency of energy use in an important concept in animal production because it impacts profitability Care must be taken when assessing efficiency of production because weight gain may be of little value in estimating caloric efficiencyData suggest that caloric efficiency is greatest for maintenance, followed by milk production, then by growth and fattening “Gross Efficiency” - Refers to the caloric value of the product over the caloric intake o Calories out/Calories in “Net Efficiency” - Is the caloric value of the product over caloric intake above maintenance o Calories out/(Calories in – Maintenance) Energy equivalents of food & alcohol The amount of energy in feedstuffs can be determined INDIRECTLY by simple measuring oxygen consumption required in metabolizing food This is often referred to as INDIRECT CALORIMETRY This approach provides the physiological energy value of feedstuffs Rule of thumb: 4:4:9 kcals/gram of CHO, protein, and fat respectively Indirect measurement of metabolic energy obtained from different feedstuff using animals Metabolism is indirectly measured by the oxygen consumed by the dog in “breaking down” the foodstuffs Heat produced by the dog is measured by noting the change in water temperature Results of these early experiments demonstrate unequivocally that energy produced through metabolism of foodstuffs is equal to heat produced in the body, but with 3 critical assumptions: - No work is being done - No growth is occurring- There is no net storage of energy (e.g., liver glycogen or fat in adipose tissue) Energy from Food components Key Fact: More energy is released from fats than from carbohydrates on a per gram basis Why? Energy is formed by the complete oxidation of carbons resulting in the formation of CO2 & metabolic water There are fewer oxygen atoms per carbon atom in fat than carbohydrates - Common fatty acid o (palmitate) C16H32O2 - Common carbohydrate o (glucose) C6H12O8 Energy in feed Key fact 2: Proteins (amino acids) have a much lower “usable” (physiologic) caloric value than predicted by gross energy content Why? All proteins contain carbon & nitrogen (N) When using proteins for energy the nitrogen in the amino acids is metabolized to ammonia (NH3) NH3 can be toxic, so the liver converts it to urea Urea contains some carbons that are not fully oxidized Thus, when urea is excreted via the kidneys, some energy is