ANN 111: Principles of Animal Nutrition and Feed Technology (2+1)

TDN IN ENERGY EVALUATION

Position of TDN in energy evaluation system:

• TDN is based on the Atwater physiological fuel values for human nutrition.
• In human after digestion and absorption the energy losses of carbohydrate and fat is negligible, only for protein there is some metabolic loss.
• So, for all three nutrients the physiological fuel values represent the metabolisable energy values.
• In case of ruminants (where the TDN system is commonly followed) even after digestion there is high gaseous loss that occurs in the form of methane and CO₂ in case of carbohydrates.
• Moreover the urinary loss is high in case of ruminant animals when compared to human beings. Hence it can be concluded that,
  • As far as carbohydrate (CF ; NFE) and fat is concerned the TDN system can be fit into DE system in ruminants.
  • In case of protein, the TDN system not only considered faecal loss but also urinary loss. So in case of protein the TDN system can be fit into ME system.
  • If the TDN system completely fits into the DE system, then the %DCP should be multiplied by a figure of 1.3.

Utility of TDN system as an energy measure:

• In India TDN system is commonly followed energy evaluation system for ruminants.
• The famous Morrison standard, which is extensively used by American farmers, is based on TDN system.
• It can be used for feeding pigs and horses and it is also reliable for comparative evaluation of ruminant rations of similar composition.
• It is often preferred to express TDN in calories of DE. DE can be calculated by multiplying TDN with a factor of 4.4. It is found experimentally that the average caloric value of 1 gram of TDN is 4.4 Kcal (= 17.5 KJ).