Nutritional Energetics of Domestic Animals and Glossary of Energy Terms (1981) / Chapter Skim
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Nutritional Energetics of Domestic Animals and Glossary of Energy Terms
Nutritional Energetics of Domestic Animals and Glossary of Energy Terms
Pages 1-44
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From page 1... ...
The total intake of food by animals feeding aa' libitum is related to their energy needs and to the concentration of available fuels in the diet. Many assumptions are required to condense the total energetics of an animal into the relatively simple tabulations used in practice to quantify the dietary energy requirements of domestic animals and man.
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Finally, the energy systems in common use within the United States and Canada for various species of domestic animals are outlined. The appendix contains a complete list of abbreviations and symbols commonly used to describe energy transactions in domestic animals.
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Ace tab olic Body Size (W'7 5 ~ is the body weight in kilograms of an animal raised to the three-fourths power. It is useful in comparing metabolic rates of mature animals of different body sizes.
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and metabolizable energy (ME) , enroute from food energy (IE)
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Therefore total intake of food energy is lE, where ~ is the amount of food consumed and E is the gross energy per unit weight of food. Similarly, total energy contained in feces is FE, where F is the amount of feces voided and E is the gross energy per unit weight of the feces.
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{E is the weight of food consumed times the gross energy of a unit weight of food. Fecal Energy (FE)
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is the intake of true digestible energy minus urine energy of food origin: TME = TDE UE + UeE. Total Heat Production (HE)
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Heat of ThermalRegulation (HcE) is the additional heat needed to maintain body temperature when environmental temperature drops below the zone of thermal neutrality, or it is the additional heat produced as the result of an animal's efforts to maintain body temperature when environmental temperature goes above the zone of thermal neutrality.
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For example, synthesis of urea from ammonia is an energy costly process in mammalian species and results in a measurable increase in total heat production. Heat Ir~cremer~t (HiE)
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The components TE, FE, UK, GE, ZE, SE, and RE are heats of combustion determined in a bomb calorimeter and represent the total energy released during the oxidation of that component to carbon dioxide and water. Other terms used to describe the heat of combustion are gross energy or' simply, energy value.
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In either case, the gross energy value does not provide any clue as to how available the energy is to the animal. Digestible energy (DE)
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However, in some investigations, particularly when feedstuffs are being compared as sources of ME, it may be advantageous to correct for Em E and UeE to obtain a true metabolizable energy value (TME)
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That is, an animal will be using energy from body tissues any time total heat production exceeds metabolizable energy intake. Relationship of Environmental Temperature to Energy Metabolism The relationship between the climatic environment and the partition of dietary and body energy into various components is related
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As effective ambient temperature rises above the upper limit of the thermoneutral zone, the animal is in the warm zone, where thermoregulatory reactions are mainly limited to passive facilitation of heat loss. Decreasing tissue insulation by vasodilation and increasing effective surface area by changing posture are major mechanisms used to facilitate rate of heat loss.
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For example, lower critical temperature may change from 0°C in a sheep with fleece to 20°C in shorn sheep, other factors remaining constant. In other words, ambient conditions are of little value in predicting the effect on energy needs unless one also knows the thermoneutral zone of the animal involved.
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, where Mm E= metabolizable energy for maintenance (kcal/day) , ~ magnitude of difference between lower critical temperature and effective ambient temperature, = total insulation of animal (kcal/T/M2 /day)
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Above the upper critical temperature, core body temperature and heat production increase, the latter according to Van't Hoff's law (Kleiber, ~ 96 ~ ) : HOE = HoE Q1O where HOE = metabolic rate at temperature T°C, Ho E = metabolic rate at 0°C, and Qua 0 = Van't Hoff~s quotient (approximately 21.
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The lower critical temperature (Tc) can be defined as the point at which the thermostatic heat requirement (heat to maintain body temperature)
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Although not precisely defined, the upper critical temperature would be expected to drop with increased intake, but in practice the animal reduces metabolic rate by reducing food consumption at high temperatures. The influence of environmental temperature on animal production is important.
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. It has been used to express the feed value and energy requirements of poultry for many years and is the general basis for the physiological fuel values used to describe the energy values of foods and the energy requirements of humans.
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True metabolizable energy (ME + Em E + UeE may be a sufficiently precise measure of the energy value of feedstuffs for those species (like poultry) whose diets are highly digestible and less variable in composition than diets fed to ruminants and nonruminant herbivores.
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may give reasonable estimates of metabolizable energy that can be used as a basis to formulate diets and approximate the requirements of humans for different functions. Net Energy Concepts The net energy (NE)
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, and energy intake that results in positive RE LU _ 1+) is LL UJ z ~ UJ cr Energy Equilibrium RE = 0 \ Fasting Energy Loss FOOD I NTAKE ( 1 )
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To express the relationship between ME, RE, HE, and NE, it is necessary to consider the following expressions: NEmr = NEm + NEr' where and NEm = ~ Oe RE - Rm E r ~ _ I but Rm E= 0 by definition and -ReE = HeE or fasting heat production. Therefore NEm = HeE/Im ~ and NE = RE -r I-Im ~These expressions are the result of the convention that describes the relationship between RE and lE (or RE and food intake, if preferred)
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Thus NEr could consist of one or several components. In a pregnant lactating dairy heifer, for example, NEr might have three major components, the energy in the milk, the energy being stored in the products of conception, and the energy stored as a result of growth (protein and fat deposition in the heifer's tissues)
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The expression to calculate kit is C3 NE k = g g ME - MEm It is immediately apparent that km and kg have a term in common. Thus NEg - kg (ME - HeE/km Sir~ce HeE is the fasting heat production and is usually expressed as awn, the equation becomes NEg = kg (ME - aWn /km
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. This is a convenient relationship for estimating kg and km if "a" is known or estimated from fasting heat production (He E)
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It is evident that systems based on the net energy concept are becoming the method of choice for expressing the energy requirements of growing ruminants. The procedures used to apply the concepts to practical conditions have been more variable.
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The convention using only NEm and NEg to state feed values and energy requirements for sheep does not give a separate allowance for woo] growth.
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The refinements of any general system to the point where it can be translated to fit with precision into all, or at least most, practical feeding situations adds to its complexity. However, the availability of inexpensive computers and programmable calculators will make it possible to use increasingly sophisticated methods to determine comparative feed values, specific animal requirements, diet formulations, and the prediction of the response of an animal to a particular diet.
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Application to Lactating Ruminants There has been a steady progression in refinement of the energy evaluation of feeds and in the understanding of energy exchanges for lactating ruminants. Requirements and feed values have been stated in all of the following energy terms: TDN, DE, ME, ENE (Morrison, 1956)
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The results of the adjustments produce a situation in which the total response of the animal to a change in energy intake is recovered as a change in milk energy output. The adjusted data were used to relate milk energy yield to the metabolizable energy intake.
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- 0.12. These relationships are all based on energy values actually measured rather than tabulated values.
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Application to Nonruminant Herbivores, Especially Horses and Rabbits Energy metabolism studies with horses are limited in number' but considerable data on digestibility are available. For this reason the system used to describe energy requirements of the horse is based on DE (NRC, 197Sb)
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. Maintenance DE, defined as zero weight change plus norms activity in the nonworking horse, is described by the equation: DEm (kcal/day)
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3. Milk production (percent of body weight)
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, starch equivalents, Scandinavian feed units, oat units, DE, ME, MEn, and NE are energy units that have been used in swine nutrition. Digestible energy defined as food intake of energy minus the fecal energy (DE = lE - FE)
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From page 38... ...
Therefore the net energy requirements and net energy values of feeds can be expressed as a single value similar to lactating ruminants (Nehring and Haeniein, 1973; Just-Nielsen, 1975; Ewan, 19761. Nehring and Haeniein (1973)
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From page 39... ...
Therefore energy requirements of swine are expressed in terms of DE or ME, but the development of a net energy system may provide a more accurate method of ration formulation for swine. Application to Poultry For many years the poultry industry relied on productive energy values to define energy requirements and to describe the available energy in feedstuffs.
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Chemical procedures have been used to measure the amount of urine in excrete, but the techniques are not wholly satisfactory. Metabolizable energy values have been measured with poultry for many years, but it was not until about ~ 960 that they became widely accepted.
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must be collected to account for all energy and nitrogen loss. Body temperature and its relationship to metabolic rate must also be considered (Smith et al., ~ 978a)
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Others have used various fecal collection methods such as removing fecal matter from the aquarium with a fine mesh net, filtration of aquarium water, and centrifugation. Each of these methods has its advantages and disadvantages.
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From page 43... ...
. Care must be taken in estimating energy values from proximate analysis.
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