Chicken diets can be calculated by designing a so-called Pearson
square
The various feedstuffs are put into two groups: high protein and low protein.
Within the group they can replace each other, so the price will decide
which one will be used more. Then the averages for each group can be
calculated according to the amounts of each ingredient used.
Suppose maize is cheaper and more plentiful than sorghum, and soy-
bean meal is cheaper than fish meal. Including all 4 ingredients makes
the feed more reliable, as the ingredients complement each other. 5 – 8
ingredients in a mixed feed may be optimal.
In our example, you can make a cereal mix with two parts of maize
(8% crude protein) and one part of sorghum (10% crude protein) from
one group, to be combined with a protein-rich mix of 3 parts of soy
bean meal (44% crude protein) and one part of fish meal (65% crude
protein):
The weighted means of the cereals and the protein feeds must be put
on the left-hand side of the Pearson square, in order to find which
combination of the two will result in the required 16.5% of protein.
The protein level required in the complete diet is placed in the middle
of the square and the percentage of protein content in each food on the
two left-hand corners of the square. To work out the proportion of
each foodstuff that is required, subtract the small number from the
larger one diagonally across the square, as shown below.
The resulting figures on the right-hand side of the square indicate the
proportion of each mixture needed to achieve a diet containing 16.5%
protein. In this case, this requires a ratio of 32.8 parts of the cereal mix
to 7.8 parts of the protein feeds (3 soybean meal : 1 fishmeal).
Expressed in percentages of the total mixture, the diet will be made up
as follows:
For the protein mix, the same procedure is used to divide the 19 % in
the ratio 1: 3
With this combination of the 4 feed ingredients, we can now calculate
whether this diet will meet the other nutrient requirements as well: see
table below
The energy content of 3,205 kcal/kg exceeds the minimum of 2,800,
the protein level is good and the crude fibre does not exceed 7%. Only
the percentage of calcium is far to low for layers. It should be between
2.5 and 3.5 %. You have to add some limestone and bone-meal to sup-
ply about 4.0 g calcium per day and to meet the calcium and phospho-
rus requirements (in a ratio of 6 :1). Alternatively, grit or broken shells
can be given separately from the feed, for voluntary intake.
The proportion of the different ingredients in the ration is more impor-
tant than the quantity you supply. Poultry will not eat any more once
their energy requirement has been met.
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