Page 156 - Calculating Agriculture Cover 20191124 STUDENT - A

14-6 Feeds and Feeding CH 14]

6. The concentrate supplement will be 26% of the total weight and the difference of the
total weight less the 200 pounds of corn.

Supplement = Total feed weight – corn weight
= 270.27# – 200#
= 70.27 # supplement

Total Digestible Nutrients (TDN) and Digestible Protein (DP)

TDN
Our agriculture researchers in feeds tell us that Total Digestible Nutrients (TDN) is the sum of
the digestible fiber, protein, lipid, and carbohydrate components of a feedstuff or diet. Total digestible
nutrients (TDN) is a measurement of the digestible organic constituents of the feedstuff. TDN is
directly related to digestible energy for the animal.
To be an accurate measure of energy, the TDN formula must factor in all of the nutrients in
animal diets that are capable of supplying energy. These are:
 Crude protein (CP). Protein is necessary for body maintenance, but any excess protein that an
animal receives can be used for energy, as well.
 Ether extract (EE). Also known as crude fat. Fat is an extremely potent source of energy, so
it is given greater weight than the other nutrients when calculating TDN. Fat is an energy
source with 2.25 times the energy density of carbohydrates.
 Crude fiber (CF). Fiber is the tough part of the plant, the part that gives it structure.
Ruminants have a specially designed digestive system to break down fiber.
 Nitrogen-free extract (NFE). Better known to most of us as simple carbohydrates. Sugars and
starches are highly digestible forms of carbohydrates, while fibers are generally less digestible.
Fiber is not included in the nitrogen-free extract part of the equation. NFE is calculated as the
percentage of feed that is not moisture, protein, fiber, fat, or ash.
To be able to calculate TDN, you will have to know the composition of the feed in question. You
will also have to know how digestible the nutrients actually are. That is, what portion of those
nutrients are used for energy in the animals use instead of being lost in the animal’s waste (expelled
as feces or urine).
The equation is:
TDN = digestible CP + (digestible EE x 2.25) + digestible CF + digestible NFE
Because any of the organic constituents could be used by the animal as a source of energy, TDN
has historically been used to describe an animal’s energy requirement and to assess a feedstuff’s
energy value for a given species. TDN is an intermediate calculation to arrive at useful nutritional
values.
The values used in the TDN equation are determined by multiplying a feedstuff’s proximate
analysis values for crude protein, crude fiber, nitrogen-free extract, and crude fat by the respective
digestion coefficients. The digestion coefficients for a particular feedstuff are found by performing a
digestion trial.
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