Bioenergetics Calculating Energy Values in Food Introduction Energy

Bioenergetics: Calculating Energy Values in Food

Introduction Energy is required by all animals to sustain life ] Sources: food, natural productivity, body stores (times of environmental stress or feed deprivation) ] Lecture objectives: How much energy is needed by aquatic organisms? , How does it varies from terrestrials? , What are the sources, how is energy partitioned for various uses ]

Lecture objectives ] How much energy is needed by aquatic organisms? ] How it varies from terrestrials? ] What are the sources? ] How is energy partitioned for various uses?

Introduction ] ] Lavoisier first demonstrated that oxidation of nutrients was some form of combustion (burning) Rubner (1894) first demonstrated that fundamental Laws of Thermodynamics also applied to intact living animal systems Organic matter processes CO 2 + H 2 O + energy (released) Understanding energy transforms is only possible when it is converted from one form to another

Introduction Energetics is the study of energy requirements and the flow of energy within systems ] bioenergetics is the study of the balance between energy intake in the form of food and energy utilization by animals for lifesustaining processes ] processes? : tissue synthesis, osmoregulation, digestion, respiration, reproduction, locomotion, etc. ]

Introduction ] the original energy source for food energy is the sun (See…I knew what I was talking about for once!) ] energy from the sun is converted by photosynthesis into the production of glucose ] ] glucose is the hydrocarbon source from which plants synthesize other organic compounds such as COH, protein, lipids as previously mentioned, one must consider the quality of these sources

Introduction ] ] ] Animals are not heat engines They can’t use the multitude of sources of energy we have (e. g. , flywheels, falling objects, the tide, etc. ) Must obtain their energy from chemical bonds of complex molecules How do they do it? In a nutshell, they oxidize these bonds to lower energy states using oxygen from the air Trick: some bonds have more energy than others

Introduction most aquaculture animals obtain their energy from feeds ] As mentioned, some bonds have more energy associated with them than others ] when you have many nutrients comprising a feed, the energy level of that feed can vary substantially ] availability of energy varies according to feed ingredient and species ] growth is the endpoint of net energy ]

Glycogen Molecule major COH storage form of energy

Lipid Molecule another major storage form

Introduction (cont. ) Energy goes through many cycles and transformations, always with loss of heat ] can be released at various rates: gasoline can exploding vs. compost pile ] nutritional energetics involves the study of the sources and transformations of energy into new products (mainly we are concerned with growth or tissue deposition) ] of all dry matter we consume, 70 -90% goes to synthesis of new products ]

Energy Forms Matter and energy are basically the same ] it is often convenient to consider energy a property of matter (kcal/g feed) ] nutritive value of food items is often reflected by calories ] what you are used to seeing in the store is not calories, but kilocalories (kcal’s), or Calorie ] common form of energy in the cell is ATP ]

Energy Forms All processes in the animal body involve changes in energy ] the word “energy” was first introduced in 1807, and defined as “ability to work” ] found in many forms: heat, kinetic, electromagnetic, radiant, nuclear and chemical ] for our purposes, chemical energy is the most important (e. g. , ATP) ]

Heat Energy The measurement of energy requires converting it from one form to another ] what we typically measure is heat (why? ) ] according to the first law of thermodynamics, all forms of energy can be converted quantitatively into heat energy ] heat energy is represented by the various constituents of the diet ]

Heat Energy ] however, the body is not a heat engine, heat is an end product of reactions ] it is only useful to animals to keep the body warm ] chemical reactions either generate heat (+ H) or require heat (- H)

Units of Heat Energy The basic unit of energy is the calorie (cal) ] it is the amount of heat required to raise the temperature of 1 g of water 1 degree Celsius (measured from 14. 5 to 15. 5 o. C) ] it is such a small unit, that most nutritionists prefer to use the kcal (or 1, 000 calories) ] REM: the kcal is more common (supermarket Calories) ]

Other Units of Heat Energy ] BTU (British Thermal Unit) = amount of heat required to raise 1 lb of water 1 o F ] international unit: the joule - 1. 0 joule = 0. 239 calories or 1 calorie = 4. 184 joule ] a joule (J) is the energy required to accelerate a mass of 1 kg at a speed of 1 m/sec a distance of 1 m

Energy Terms (from De Silva and Anderson) ] Energy flow is often shown as a diagram: every text has its own idea of a suitable diagram:

Energy Terms Gross energy (GE): energy released as heat resulting from combustion (kcal/g) ] Intake Energy (IE): gross energy consumed in food (COH, lipid, protein) ] Fecal Energy (FE): gross energy of feces (undigested feed, metabolic products, gut epithelial cells, digestive enzymes, excretory products) ] Digestible Energy (DE): IE-FE ]

Energy Terms (cont. ) ] ] Metabolizable energy (ME): energy in the food minus that lost in feces, urine and through gill excretion: ME = IE - (FE + UE + ZE) urinary energy (UE): total gross energy of urinary products of unused ingested compounds and metabolic products gill excretion energy (ZE): gross energy of products excreted through gills (lungs in mammalian terrestrials), high in fish surface energy (SE): energy lost to sloughing of mucus, scales, exoskeleton

Energy Terms (cont. ) Total heat production (HE): energy lost in the form of heat ] heat lost is sourced from metabolism, thus, HE is an estimate of metabolic rate ] measured by temperature change (calorimetry) or oxygen consumption rate ] divided into a number of constituents ] as per energy flow diagram ]

Energy Flow Diagram

Energy (total heat ] ] ] Terms production) Basic metabolic rate (He. E): heat energy released from cellular activity, respiration, blood circulation, etc. heat of activity (Hj. E): heat produced by muscular activity (locomotion, maintaining position in water) heat of thermal regulation (Hc. E): heat produced to maintain body temp (above zone of thermal neutrality) heat of waste formation (Hw. E): heat associated with production of waste products specific dynamic action (Hi. E): increase in heat production following consumption of feed (result of metab), varies with energy content of food, especially protein

Energy Utilization ] ] ] Energy intake is divided among all energy-requiring processes Magnitude of each depends on quantity of intake plus animal’s ability to digest and utilize that energy Can vary by feeding mode: carnivorous vs. herbivorous From Halver (page 7)

Focus: Gross Energy content of a substance (i. e. , food) is typically determined by completely oxidizing (burning) the compound to carbon dioxide, water and other gases ] the amount of energy given off is measured and known as gross energy ] gross energy (GE) is measured by a device known as a bomb calorimeter ]

Gross Energy of Feedstuffs

Gross Energy of Feedstuffs Fats (triglycerides) have about twice the GE as carbohydrates ] this is because of the relative amounts of oxygen, hydrogen and carbon in the compounds ] energy is derived from the heat of combustion of these elements: C= 8 kcal/g, H= 34. 5, etc. ] typical heat from combustion of fat is 9. 45 kcal/g, protein is 5. 45, COH is 3. 75 ]

Available Energy ] ] ] Gross energy only represents the energy present in dry matter (DM) it is not a measurement of its energy value to the consuming animal!! the difference between gross energy and energy available to the animal varies greatly for different foodstuffs the key factor to know is how digestible the food item is digestible energy also varies by species

Digestible Energy The amount of energy available to an animal from a feedstuff is known as its digestible energy (DE) ] REM: DE is defined as the difference between the gross energy of the feed item consumed (IE) and the energy lost in the feces (FE) ] two methods of determination: direct or indirect ] by the direct method, all feed items consumed and feces excreted are measured ]

Digestible Energy The indirect method involves only collecting a sample of the feed and feces ] digestion coefficients are calculated on the basis of ratios of energy to indicator in the feed and feces ] indicator? : an inert indigestible compound added to the feed ] indicators: natural (fiber, ash) or synthetic (chromic oxide) ]

DE Calculations Direct Method Feed energy - Fecal energy % DE = X 100 Feed energy Indirect Method % DE = 100 - Feed energy Fecal energy X Fecal indicator Feed indicator x 100

Metabolizable Energy Even more detailed! ] Represents DE minus energy lost from the body through gill and urinary wastes ] More difficult to determine! Why? ] REM: all urinary wastes in water!!! How do you collect that? ? ] Intake energy - (E lost in feces, urine, gills) %ME = ------------------- x 100 Feed energy

Metabolizable Energy Use of ME vs DE would allow for a much more absolute evaluation of the dietary energy metabolized by tissues ] however, ME offers little advantage over DE because most energy is used for digestion in fish ] energy losses in fish through urine and gills does not vary much by feedstuff ] fecal energy loss is more important ] forcing a fish to eat involuntarily is not a good representation of actual energy processes ]

Energy Ratios for Rainbow Trout

Energy Balance in Fish ] ] ] Energy flow in fish is similar to that in mammals and birds fish are more efficient in energy use energy losses in urine and gill excretions are lower in fish because 85% of nitrogenous waste is excreted as ammonia (vs. urea in mammals and uric acid in birds) heat increment (increase) as a result of ingesting feed is 3 -5% ME in fish vs. 30% in mammals maintenance energy requirements are lower because they don’t regulate body temp they use less energy to maintain position

Terrestrials vs. Aquatics This section concerns the requirements for energy by aquatic animals, how energy is partitioned, what it is used for and how it is measured ] a major difference in nutrition between fish and farm animals is the amount of energy required for protein synthesis ] protein synthesis refers to the building of proteins for tissue replacement, cell structure, enzymes, hormones, etc. ] fish/shrimp have a lower dietary energy requirement ]

Factors Affecting Energy Partitioning Factors either affect basal metabolic rate (e. g. , body size) or affect other changes ] those affecting BMR are the following: body size: non-linear, y = axb, for most physiological variables, b values usually range between 0. 7 and 0. 8 oxygen availability: have conformers (linear) and non-conformers (constant until stressed) ]

O 2 Consumption, by Size (Fig. 2. 1 from De Silva and Anderson)

Factors Affecting Energy Partitioning temperature: most aquaculture species are poikilotherms, significant effect, acclimation required, aquaculture situation may mean rapid temp changes osmoregulation: changes in salinity result in increased cost of energy stress: increased BMR resulting from heightened levels of waste, low oxygen, crowding, handling, pollution, etc. (manifested by hypoglycemia) cycling: various animal processes are cyclic in nature (e. g. , reproduction, migration)

Factors Affecting Energy Partitioning Those factors not affecting BMR are: gonadal growth: most energy diverted from muscle growth into oogenesis, deposition of lipid, can represent 30 -40% of body weight, implications? ? locomotion: major part of energy consumption, varies due to body shape, behavior and size, aquatic vs. terrestrial issues ]

Another Index: Gross Conversion Efficiency (K) Referred to as “K”, often used as an indicator of the bioenergetic physiology of fish under various conditions ] does not refer to an energy “budget” ] measures growth rate (SGR) relative to feed intake over similar time periods ] both factors are related to body size: ] K = (SGR/RFI) x 100 SGR = (ln Wtf-ln. Wti)/(Tf - Ti) x 100 ] RFI = (feed intake)/((0. 5)(Wtf -Wti)(Tf-Ti)) ]

Energy and Growth ] ] ] Dietary excesses or deficiencies of useful energy can reduce growth rate this is because energy must be used for maintenance and voluntary activity before it is used for growth dietary protein will be used for energy when the diet is deficient in energy relative to protein when the diet contains excessive energy, feed intake is typically reduced. . . fish don’t want to be fat? ? this also reduces intake of protein and other nutrients needed for growth

Dietary Sources of Energy: proteins ] ] ] ] Considerable interaction between major nutrient groups as energy sources protein can be used as an energy source not typically used because of cost and use for protein synthesis (growth) optimal ratio of protein: energy is around 22 mg PRO/k. J (45 k. J/g PRO; old info) species variation: 17 (59) for tilapia, 29 (35)for catfish, 29 (34) for mutton snapper (Watanabe, et al. , 2001); digestibility variation temperature variation

Energy and Growth Consumption of diets with low protein to energy ratios can lead to fat deposition (fatty acid synthetase) ] this is undesirable in food fish because it reduces the dress-out yield and shortens shelf life ] undesirable in shrimp due to build-up in hepatopancreas (midgut), ultimately affecting cooking ] low protein: energy diets can be useful for maturation animals, hatchery animals raised for release ]

Energy Requirments of Fish Determining the energy requirement of fish has been a difficult task, slow in coming ] most research has been devoted to identifying protein requirements, major minerals and vitamins ] in the past, feeds were formulated letting energy values “float” ] excess or deficiency of nutritional energy does not often lead to poor health ]

Energy Requirements of Fish Further, if feeds are formulated with practical feedstuffs (ingredients), their energy levels are not likely to be off ] it is really a matter of cost: protein is the most expensive component of the diet, COH sources are cheap, why use protein as an energy source? ? ] In terrestrials, feed is consumed to meet energy requirements ] thus, as energy level of the feed goes up, protein level is also designed to go up ]

Energy Requirements of Fish This is because terrestrial animals are typically fed on an ad libitum basis ] fish, on the other hand, aren’t fed this way ] they are fed on a feed allowance basis (we estimate feed fed) ] various studies have shown that the digestible energy (DE) requirement for channel catfish and carp was around 8. 3 -9. 7 kcal DE/100 g fish/day ] in terms of age, dietary level of DE and protein typically drop with age ]

Protein, DE Requirements of Channel Catfish, by Age From Lovell, 1989

Energy Requirements of Fish DE and protein requirements typically follow each other, so the DE: P ratio (kcal/g) is fairly similar with age (if anything, a small increase) ] this is partially due to the fact that fish grow faster when young (higher tissue turnover rate, demand for protein) ] however, the influence of energy is stronger than that of protein relative to growth (Cuzon and Guillaume, 1997) ] energy levels in crustacean diets usually range similar to those of fish ]

Energy Requirements of Aquatics The objective in formulating diets for most aquatic species is the same: finding a cheap energy source that is digestible and will spare protein ] glucose is not acceptable in that it causes high blood sugar levels, poor growth, poor survival ] complex dietary COH’s prove better ] COH typically spares protein for growth ] increase in dietary energy tends to increase performance when a diet low in protein is fed ]

Energy Problems Lipids and carbohydrates are typical energy sources for crustaceans ] unfortunately, crustaceans are unable to tolerate diets having greater than 10% lipid (also hard to manufacture the feed!) ] this means that the major energy source must be derived from COH ] various COH are used to various degrees by crustaceans, making it difficult to calculate the true energy value of diets ]