what the chief methods of measure the net energy
Dear Zahira
The NE system does a better job of estimating the available energy in ingredients and diets. However, there is still confusion regarding the derivation of values used in the NE system.
Determining the NE content of either an ingredient or a diet is much more complex than either Digestible Energy DE or Metabolisable Energy ME.. Indirect calorimetry provide s a direct estimate of heat loss while predictive equations have been developed using indirect calorimetry as a reference. Each technique has benefits and limitations which should be understood by anyone using these values.
Dear Zahira
The NE system does a better job of estimating the available energy in ingredients and diets. However, there is still confusion regarding the derivation of values used in the NE system.
Determining the NE content of either an ingredient or a diet is much more complex than either Digestible Energy DE or Metabolisable Energy ME.. Indirect calorimetry provide s a direct estimate of heat loss while predictive equations have been developed using indirect calorimetry as a reference. Each technique has benefits and limitations which should be understood by anyone using these values.
Although this is only an approximation, typically about 10% of the energy content of food is required for the process of digestion. The metabolizable energy is approximately 4 kcal/gram for carbohydrates and proteins and 9 kcal/gram for fats. Thus the net energy would be approximately 3 1/2 kcal/gram for carbohydrates and proteins and 8 kcal/gram for fats. But for proteins considerable energy is lost in nitrogenous waste products, reducing the net value further, typically to about 5 1/2 kcal/gram. Hopefully this is may be helpful, even though it is only an approximation. The percentage of energy required for digestion varies with the food. (In the above we count energy liberated as heat as part of the net energy, since it is useful in maintaining body temperature, as is true except in hot summer weather. In some definitions of net energy, only the part used in muscular work, in operation of the brain, in repair, etc., but not as heat, is counted as net energy. Typically the efficiency of conversion of metabolizable energy to muscular work is in the range of 25% to 40%.)
hi
Net Energy Gain (NEG) is a concept used in energy economics that refers to the difference between the energy expended to harvest an energy source and the amount of energy gained from that harvest.[1] The net energy gain, which can be expressed in joules, differs from the net financial gain that may result from the energy harvesting process, in that various sources of energy (e.g. natural gas, coal, etc.) can be priced differently for the same amount of energy.
A net energy gain is achieved by expending less energy acquiring a source of energy than is contained in the source to be consumed. That is
{\displaystyle NEG=Energy_{\hbox{Consumable}}-Energy_{\hbox{Expended}}.}
Factors to consider when calculating NEG is the type of energy, the way energy is used and acquired, and the methods used to store or transport the energy. It is also possible to overcomplicate the equation by an infinite number of externalities and inefficiencies that may be present during the energy harvesting process.
H
Determining the NE content of either an ingredient or a diet is much more complex than either Digestible Energy or Metabolisable Energy.
Regards.
Several researchers have developed equations that predict the NE content of a feed or diet. Depending on the equation chosen, these require knowledge of various nutrients or digestible nutrients in the feed as inputs. Most of these equations have been developed from experiments using indirect calorimetry (below). Examples of equations in common use are:
NE, kcal/kg DM = 2.892 DCP + 0.8.365 DEE + 3.418 starch + 2.84 sugars + 2.055 Dres
NE, kcal/kg DM = 0.703 DE + 1.58 EE + 0.48 starch – 0.98 CP – 0.98 CF
(cited as NE2v and NE4 respectively in Noblet (1994) and Sauvant (2004). DCP = digestible crude protein, DEE= digestible ether extract, Dres = digestible organic matter – (DCP + DEE+starch +DCF), DE = digestible energy, EE = ether extract, CP = crude protein and CF = crude fibre
Using these equations requires knowledge of digestible nutrient content of a feed. Moreover, care has to be taken that characterisation of the digestible nutrient content is conducted using similar methodology (lab analyses etc.) that were used to develop the equation.
http://www.thepigsite.com/articles/3984/determining-the-net-energy-content-of-diets-and-ingredients/
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