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

TOTAL DIGESTIBLE NUTRIENTS

• This is the simplest form of energy evaluation wherein the animal requirements and the value of feeds in meeting these requirements are expressed in terms of the weight of digestible material in the feed.
• The digestibility of nutrients is determined by digestibility trials.
• TDN is simply a figure, which indicates the relative energy value of a feed to animals.
• It is ordinarily expressed in Kg or in percent.
• It can be calculated by the formula

TDN (%) = % digestible crude protein + % digestible crude fibre + % digestible N-free extract + (2.25 x % digestible ether extract).

% TDN =  % DCP + % DCF + % DNFE +(2.25 x % DEE)

• The digestible ether extract is multiplied by 2.25 because on oxidation fat provides 2.25 times more energy as compared to carbohydrates.
• The digestible protein is included in this equation because of the fact that excess of protein eaten by the animals serve as a source of energy to the body.
• The principle of determining the TDN of feed is essentially the same as proposed by Henneberg and Stohkmann at the Weende’s experiment station.
• The feed and faeces are subjected to the proximate analysis namely, CP, EE, CF and NFE.
• The amounts of these nutrients not recovered in the faeces are considered to be digested.