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

MERITS AND LIMITATIONS

Merits:

• It is easiest to determine the digestible values through digestive trials unlike the ME and NE, which require complicated equipments and procedures.
• The TDN values for most of the feedstuffs are obtained from carefully conducted digestion trial and are available in standard books.
• The energy requirements of the ruminant were in TDN values.

Limitations:

• Only the loss in faeces is accounted for in this method, but losses in combustible gases, heat of fermentation and urine are not considered. This is a strong limitation to the usefulness of TDN for evaluating feeds for ruminants.
• It over estimates the value of roughages. This is because the losses in methane and heat are relatively larger per unit TDN for roughages than for concentrate Eg. 1 kg of TDN in low-grade roughage contains only 50% of the net energy present in 1 kg of TDN in maize grain. Thus, low quality feeds are over estimated by the TDN system.
• If feeds are high in fat content, the TDN value some time exceed 100 in percentage (Eg.) Pure fat which has 100% digestibility would theoretically have a TDN value of 225% (100 x 2.25 = 225). Animal fat – 175%, maize oil – 172%.
• The term total digestible nutrients consider only the energy giving nutrients whereas the micronutrients like minerals have not been included.