Bioenergetics

1. Bioenergetics

2. Homeostasis Definition The state of sustained equilibrium in which all cells, and all life forms, exist Integration of all pathways In different ‘metabolic situations’ Utilization of nutrients

3. Bioenergetics The study of energy supply, utilization and dissipation Energy is the capacity for performing work Nutrients contain chemical energy which is yielded upon metabolism Used for chemical, mechanical, electrical or osmotic work

4. Functions of Energy Energy = ability to perform work Mechanical work Formation of substrates Active transport Transfer of genetic information Maintenance

5. Energy • Released energy is trapped in high energy phosphate bonds

6. Pathways of Metabolism

7. The Basics… The “Energy Balance Equation” Energy In = Energy Out + Energy to Stores Remember that energy can be neither created nor destroyed If you eat it, it has to either be used or stored or excreted This is not rocket science…

8. Energy 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 maintenance

9. What makes up energy in? Simply, the amount of energy ingested in feedstuffs 4 kcal/g carbohydrate 4 kcal/g protein 9 kcal/g fat 7 kcal/g alcohol

10. Energy Units Joule Joule = kg/(m2●s2) Older unit still used in the US is calorie (cal) 1 calorie = heat required to increase the temperature of one gram of water from 14.5 to 15.5°C 1 calorie = 4.184 J More frequently used measurements 1000 calories = 1 kcal 1000 kcal = 1 Mcal

11. Formation and Use of Energy

12. Efficiency Efficiency of conversion of chemical to work energy is less than 25% Remainder is converted to thermal energy (i.e., heat)

13. Efficiency of Converting Feed

14. Energy Value of Selected Feeds

15. Overview of Energy Metabolism Productive Functions: Feed Heat Water Protein Fat CHO Mineral Vitamin Maintenance Growth Work Lactation Gestation Nutrients to Tissues Feces Gas Urine

16. Need to Get a Useful Energy Value • Fecal loss is significant in all animals • Total Digestible Nutrient (TDN) system attempted to improve energy value by adjusting for digestibility • TDN does not account for other potential losses - particularly those associated with fermentation

17. Total 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 DE

18. Total Digestible Nutrients

19. Net 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 form

20. Energy Partitioning Gross Energy (GE) Energy Lost In feces (FE) Digestible Energy (DE) In urine and gases (UE and GPD) Energy Lost Metabolizable Energy (ME) Energy Lost In heat (HI) Net Energy (NE) NEm NEg NEl

21. Gross Energy (GE) • Represents total energy content of feed • Heat of combustion • Bomb calorimeter • Energy released as heat when a feed if completely oxidized to CO2 and H2O • Provides little information on nutrient utilization

22. Net Energy System Gross Energy (GE) Digestible energy (DE) Fecal energy Undigested feed residues Metabolic products Mucosa Bacteria Enzymes

23. Digestible Energy (DE) DE = GE – fecal energy Apparent digestibility Provides some assessment value Similar to TDN Major weakness Overestimates value of high fiber diets

24. Fecal Energy (FE) Largest energy loss Two sources: Undigested food Indigestible Increased rate of passage Endogenous Active secretion Cells slough Undigested microbes and their metabolites

25. Digestible Energy (DE) Losses for ruminants (cattle and sheep) 40-50% for roughages 20-30% for grains Losses for horses are 35-40% Used by horse NRC Losses for pigs are 20%

26. Energy Value of Selected Feeds

27. Net Energy System Digestible Energy (DE) Metabolizable energy (ME) Urinary energy N disposal and Gaseous energy Gaseous products of fermentation (CH4) - lost via belching or bowels

28. Metabolizable Energy (ME) ME = DE – gas and urine (UE) energy Greater assessment value than DE Used by swine and poultry NRC Used in human nutrition Can be calculated from DE (rather than directly measured)

29. Urinary Energy (UE) Total gross energy in urine Includes energy from: Nonutilized 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 cattle

30. Gaseous Energy Methane (CH4) is main form lost as gas 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 indirectly

31. Energy Value of Selected Feeds

32. Net Energy System Metabolizable Energy (ME) Net energy (NE) Heat increment energy Heat of digestive fermentations and actions Heat of metabolism

33. Net Energy (NE) NE = ME – heat increment (HI) NEm, NEg, Nel Maintenance, gain and lactation Best indication of energy available for maintenance and production Used by beef, dairy and sheep NRC

34. Heat Increment (HI) Can represent 25-40% of gross energy intake 2nd largest energy loss Lowest HI for fat Highest HI for fiber Losses of energy as heat: Basal metabolism Muscular activity Digestion and absorption Microbial fermentation Product formation Waste formation and excretion Thermal regulation

35. Net Energy (NE) End products of digestion are used at different levels of efficiency for various functions Not possible to assign a single NE value to a feedstuff Corn grain (Mcal/kg): 2.16 NEm 1.48 NEg 2.05 NEl

36. Energy Value of Selected Feeds

37. Net Energy System Production (NEg or NEl) Tissue growth Stored in products Work Net Energy (NE) Maintenance (NEm) Basal metabolism Activity at maintenance Sustaining body temperature

38. NEm Quantity of energy an animal would use to form tissue, fat and protein to stay alive Quantity of feed necessary to prevent tissue loss from an animal’s body

39. Maintenance The amount of energy (or protein) needed to maintain an animal in zero energy (or protein) balance Strictly speaking, only applies to a mature, non-pregnant, non-lactating animal But in practice the concept is widely applied to productive animals

40. Efficiency Maintenance feed requirements have a major effect on efficiency of feed utilization >40% energy intake is used to support maintenance

41. Total Net Energy 26% 52% 79% 40%

42. Maintenance Energy Components Maintenance Energy Requirement Basal Metabolism Muscular Work Temperature Regulation

43. Basal Metabolism Metabolic rate in postabsorptive state, with minimal activity, thermal and psychic stress, needed to sustain life Basal metabolic rate (BMR) Maintains cellular activity, respiration, and blood circulation Affected by Body size Species Age Previous level of nutrition Climate

44. Contribution of Specific Organs:Mature Sheep Maintenance Costs

45. Body Size • The bigger an animal, the more heat it produces • Relationship is curvilinear

46. Body Size • Plotted on logarithmic scale • Relationship becomes linear

47. Metabolic Body Size W0.75 Used to compare mature animals of different body size Used to determine maintenance energy requirements Heat dissipation correlated to body surface area Used to compare metabolism of different species

48. Metabolic Body Size

49. Age Basal heat production, corrected for metabolic body weight, declines quickly from birth to weaning, then more slowly to maturity

50. Climate Prolonged cold causes increased basal heat production Prolonged heat caused decreased basal heat production