1) The document discusses the partitioning of feed energy as it moves through an animal's digestive system. Gross energy is reduced to digestible, metabolizable, and net energy values as energy is lost through feces, urine, methane, and heat production. 2) Key factors that affect energy values include the composition of the feed, processing methods, animal species, and feeding level. Roughages have lower energy values than concentrates due to greater losses. 3) Several systems are used to evaluate and express the energy value of feeds, including total digestible nutrients (TDN), starch equivalents, gross energy, and net energy. Each system accounts for energy losses in different ways.

1. Partitioning of feed energy
K.GURU MOHAN REDDY
TVM/2016-13
DEPARTMENT OF ANIMAL NUTRTION
COLLEGE OF VETERINARY SCIENCE, TIRUPATI
SRI VENKATESWARA VETERINARY UNIVERSITY

2. Gross energy
Fecal energy
Digestible energy
Loss in urine &
methane
metabolizabile energy
Losses in
Heat Increment
Net energy
Use for maintainance use for production

3. • GROSS ENERGY
• Animal food is composed of proteins, fats and carbohydrates besides
mineral, vitamins etc.
• In considering the energy requirement body purposes, the proteins,
fats and carbohydrates are grouped together.
• Gross energy is the total heat of combustion of a material as
determined with a bomb calorimeter-ordinarily expressed as
kilocalories per kilogram of feed or mega joule/kg dry matter.

4. • The gross energy value of a feed has no relationship to the feeds
digestible, metabolizable or net energy values, except that the latter can
never exceeded the GE.
• Certain products such as coal, mineral oil and lignin have high gross energy
values but, because of their indigestibility are of no energy value to the
animal.
• Roughages have gross energy values comparable concentrates, but the two
differ greatly in digestible, metabolizableand net energy values.

5. • Fat, because of their greater proportion of carbon and hydrogen,
yield 2.25 times more gross energy per kg than carbohydrates and
protein
• Energy supplied by the food in excess of that needed for maintenance
is used for the various forms of production.
• A young growing animal will store energy principally in the protein of
its new tissues, a fattening animal stores energy in fat, and a lactating
animal will transfer food energy into milk.

6. • DIGESTIBLE ENERGY
• This is that portion of the gross energy of a feed which does not appear in
the faeces.
• It include metabolizable energy as well as the energy of the urine and
methane.
• The undigested food nutrient present in faeces can burnt in bomb
calorimeter produced enough heat.
• This means that considerable quantity of heat of the digested food is
eliminated in the faeces.

7. • METABOLIZABLE ENERGY (ME)
• It is that portion of gross energy not appearing in the faeces, urine
and gases of fermentation (Principally methane).
• It is digestible energy minus energy of the urine and methane.
• It is comparable energy of TDN minus the energy of the fermentation
gases.
• Metabolizable energy = Energy in the food - (Energy lost in faeces +
energy lost in combustible gases + energy lost in urine).

8. • Normally about 8 per cent of the gross energy intake is lost through the
methane production.
• Metabolizable energy can also be calculated from the digestible energy by
multiplying with 0.82 which means roughly about 18 per cent of the energy is lost
through urine and methane.
• ME = DE * 0.82

9. • Factors Affecting the Metabolizable Energy Values of Foods
• Species of animals
• Composition of feed
• Processing of food
• Level of feeding

10. • 1. Species of animals.
• The metabolizable energy of feeding stuffs varies according to the
species to which it is being fed.
• In the ruminants about 8-10 per cent losses of energy are in the
methane production while in the non-ruminants there are no such
losses.
• Therefore, the ME values are higher in non-ruminants than for the
ruminants. This gap is more in the feeding stuffs rich in the crude
fibre.

11. • 2. Composition of feed.
• If the crude protein present in the food is unbalanced then
• the majority of the amino acids will be determined
• and greater proportion of the amino acids will be deaminated
• and greater proportion of nitrogen will be excreted as urea.
• One gram of urea excreted will be equivalent to 23.00 KJ of energy

12. • Therefore, generally the ME values are frequently corrected to zero
nitrogen balance.
• For ruminant a factor of 31.17 KJ per gram of nitrogen has been used
• For poultry the factor is 34.39 KJ per gram

13. • 3.Processing of food.
• Processing of food also affect the ME values since it affects the losses
of nutrients in faeces and methane production.
• 4.Level of feeding.
• The level at which feed is being fed affect the ME value of the feed.
• At high level of intake ME values are reduced.

14. • NET ENERGY (NE)
• This is that portion of metabolizable energy which may be used as
needed by the animals for work, growth, fattening, fetal
development, milk production, and/or heat production.
• It differs from metabolizable energy in that net energy does not
include the heat of fermentation and nutrient metabolism or the
heat increment.
• Net energy is not used for heat production unless however and above
that from other sources is required to keep the animal warm.

15. • It is important to understand that of the heat lost by the animal only
a part, the heat increment of the food, is truly waste energy which
can be regarded as a direct tax on the food energy.
• The heat increment or the expenditure of energy during the
assimilation of feed was accounted for the Armsby in the following
manner.
• He measured the heat resulting from ingestion of a feed at a given
level of food intake in animal calorimeter .

16. • He then increased the intake of food
• And by a second measurement he found out the differences, which he
called the heat increment or specific dynamic effect of food.
• This heat is useful only for keeping an animal warm during very cold
weather.
• At other times the energy represented by this heat is not only a complete
loss but also may actually interfere with production by causing the animals
to be too warm.

17. Evaluation of Energy Value of
Feed

18. • For expressing the energy value of feeds and requirements of
animals, various systems are followed in different countries are as
follows :
• Total digestible nutrients (TDN)
• Starch equivalent (SE)
• Gross energy (GE)
• Digestible energy (DE)
• Metabolizable energy (ME)
• Net energy (NE)
• Scandinavian food unit
• Mollgaard's values
• Frap's production value

19. • TOTAL DIGESTIBLE NUTRIENTS (TDN)
• TDN is simply a figure which indicates the relative energy values of a
feed to an animals.
• It is ordinarily expressed in pounds or kilogram's or in percent (pound
or kg of TDN per 100 pound or kg of feed).
• It is arrived at by adding together the following
• % TDN = % DCP + % DCF + % DNFE + (% DEE* 2.25)

20. • The percentage TDN content of any feed represents energy of heat
value of that particular feed.
• Since fat on oxidation provides 2.25 time more energy as compared
to carbohydrates, hence the figure is multiple by 2.25.
• The protein in this equation has been included because of the fact
that excess of protein eaten by the animals serve as a source of
energy to the body.

21. • Limitation of the TDN System
• 1. It over estimates the value of roughages because more energy
spent in chewing of such feeds remains unaccounted.
• 2. Only the loss in faeces is accounted for in this method.
• 3. If feeds are high in fat content will some time exceed 100 in
percentage of TDN

22. • Factors Affecting the TDN Value of a Feed
• The percentage of the dry matter
• The digestibility of the dry matter
• The amount of mineral matter in the digestible dry matter.
• The amount of fat in the digestible dry matter

23. The percentage of the dry matter.
• The more water present in feed, the less there is of other
nutrients, and, other things being equal, the lower the TDN
value.
The digestibility of the dry matter.
• Unless the dry matter of a feed is digestible, it can have no TDN
value.
• Only digestible dry matter can contribute TDN.
• Lignin has a high energy value but it can not be digested by the
animals so has no digestible energy or TDN values.

24. • The amount of mineral matter in the digestible dry matter.
• Mineral contribute no energy to the animal though mineral compounds
are digestible but have no TDN value.
• The more mineral matter a feed contains, other things being equals, the
lower will be its TDN values.
• The amount of fat in the digestible dry matter.
• The feeds high in digestible fat some time TDN value exceed 100%.
• In fact, a pure fat which had a coefficient of digestibility of 100% would
theoretically have a TDN value of 225% (100 x 2.25 1 225).

25. • THE STARCH EQUIVALENT
• KelIner, in Germany with steers in a respiration apparatus, measured
the values of feeds for productive purposes in terms of starch values,
instead of net energy values.
• In this system 1 pound of digestible starch is taken as the net energy
unit
• Using the nitrogen-carbon-balance method the starch equivalent can
be calculated from the following equation :
• SE = (Weight of fat stored per unit of food / Weight of fat stored
per unit weight of starch ) *100

26. • Kellner added pure carbohydrate, protein and fat to a basal
maintenance ration to determined the relative amounts of these pure
digestible nutrients required to produce a unit of body fat using the
nitrogen-carbon-balance method.
• One kg of digestible proteins produces 235 grams of fat
• One kg of digestible starch and cellulose produces 248 grams of fat
• One kg of digestible cane sugar produces 188 grams of fat
• One kg of digestible fat produces 474 to 598 grams of fat

27. • Taking starch as the unit, the fat producing power of proton, f fats and
carbohydrates was then calculated by him as follows :
• One part digestible protein = 235/248 =0.95 starch equivalent (SE)
• One part of digestible fat = 474/248 to 598/248 = 1.91 to 2.41 (SE)
• One part of digestible starch = 248 / 248 = 1.00(SE)

28. • SCANDINAVIAN FEED UNIT SYSTEM
• The Scandinavian feed unit system of valuing feed is widely used in the
Scandinavian countries for measuring the relative values of different feeds.
• In this ,the value of 1 pound of barley grain is taken as the standard.
• The feed unit value for any other feed is the amount of that feed which is
estimated to have same Productive value as 1.00 pound barley.

29. • For example, the feed unit values of soybean oil meal and cotton seed
meal for dairy cows are 0.85 pound and the value for corn grain is
0.95.
• This system has the merit of comparing the values of food on the
basis of actual result when applied in practice.
• Consequently any specific value that the food may possess in
addition to its protein and energy values receives proper recognition

30. • MOLLGAARD’S VALUE
• Mollgaard, who has conducted extensive respiration studies with dairy cow
in Denmark, has published feed units for milk production or production
units, of a somewhat different kind.
• For feeds which values has not been determined experimentally, values
were computed from Kellner’s starch value, or from the content of
digestible nutrients.
• In his value recognition is given to the fact that the net energy values of
feed are higher for milk production than for fattening animals

31. • FRAP’S PRODUCTIVE VALUES
• From extensive studies of the results of feeding experiments in which
various feeds have been compared.
• Fraps of the Taxas station computed net energy values expressed in therm.
He called these values as productive energy values.
• He also derives production coefficients for a considerable list of feed by
means of which approximate net energy values can be computed from the
chemical composition.