Protein quality
Evaluation of Protein Value of Feed in Animal Nutrition
It has long been known that all animals must receive in their food at least a certain minimum
amount of protein. For simple stomach animals, the quality or kind of protein is fully as
important as the amount. Fortunately, ruminant has much more simple requirement for protein
than non-ruminants. This is because the rumen micro-organisms are able to use very simple
nitrogen compounds as a protein source. This microbial protein is used by the ruminants.
Different approaches to the evaluation of protein sources are therefore necessary for ruminant
and non-ruminant animals.
Crude Protein (CP): Crude protein in the feed stuffs is estimated by determining the nitrogen
content of feed and multiplying it by a factor 6.25. Two assumptions are made in calculating the
protein content from the nitrogen: firstly, that all the nitrogen of the food is present as protein
and secondly that all food protein contains 16g N/100g. The nitrogen content of the food is then
expressed in term of crude protein (CP) calculated as follows. CP (g/100g) = g nitrogen /100g x
100/16 Or more commonly CP (g/100g) = g nitrogen /100g x 6.25
Both above assumptions are unsound. Different food proteins have different nitrogen contents,
and therefore different factors should be used in the conversion of nitrogen for individual food.
The nitrogen content of a number of common proteins together with appropriate nitrogen
conversion factor is shown as:
Food protein Nitrogen (g/lOOg) Conversion factor
Cotton seed 18.87 5.30
Soyabean 17.51 5.71
Barely 17.15 5.83
Oat 17.15 5.83
Wheat 17.15 5.83
Maize 16.00 6.25
Egg 16.00 6.25
Meat 16.00 6.25
Milk 15.68 6.38
1
, True Protein (TP): The term true protein is used to denote the protein only. It can be separated
from non-protein nitrogen by precipitation with cupric hydroxide or by heat coagulation. The
protein is then filtered and residue subjected to nitrogen estimation by Kjeldahl method. The
protein is determined by multiplied the factor 6.25.
Digestible Crude Protein (DCP): When the crude protein content of the feed stuffs is
multiplied by its digestibility coefficient, it gives the digestible crude protein. It is the most
common way of expressing the protein values and requirement of the ruminants on most of the
countries. In India, DCP is taken as the measure for expressing the protein values of feeds for
ruminants. Digestible crude protein figures are not entirely satisfactory assessments of protein,
because the efficiency with which the absorbed protein is used differs considerably from one
source to another.
Protein Equivalent (PE): In some of the European countries protein equivalent is used instead
of DCP. In protein equivalent non-protein nitrogen fraction is given half the nutritive of the true
protein and is calculated as follows:
PE= %DCP+ % DTP 2 So PE is the arithmetic mean of the percentage of DCP and DTP.
Protein Quality (PQ): In ruminants protein quality is not given much of the importance since all
the essential amino acids can be synthesized by microbs
Evaluation of Protem
Value of Feed in Animal Nutrition are synthesized in the rumen by the synthesis of microbial
proteins. However, digestible crude protein value for nonruminant animal is not adequate to
express the protein value. It is important to know how much of the absorbed protein is used by
the animal body. This utilization will be different with the various protein sources as it is
dependent upon the amino acid composition of the protein.
Evaluation of protein value of feed in non-ruminants:
Protein Efficiency Ratio (PER): The protein efficiency ratio normally uses growth of the rat as
a measure of the nutritive value of dietary protein. It is defined as the weight gain per unit weight
of protein eaten, and may be calculated by the following formula. . .. .)
Protem efficiency ratio = Gain in body weight (g )/'Protein consumed (g)
The PER values will vary with different protein sources as the composition of protein varies with
regard to essential amino acids. For the optimum rate of growth, various level of protein would
be required depending upon the quality. On this basis comparison between different sources of
protein can be made. It is simplest method for evaluating protein quality.
2
Evaluation of Protein Value of Feed in Animal Nutrition
It has long been known that all animals must receive in their food at least a certain minimum
amount of protein. For simple stomach animals, the quality or kind of protein is fully as
important as the amount. Fortunately, ruminant has much more simple requirement for protein
than non-ruminants. This is because the rumen micro-organisms are able to use very simple
nitrogen compounds as a protein source. This microbial protein is used by the ruminants.
Different approaches to the evaluation of protein sources are therefore necessary for ruminant
and non-ruminant animals.
Crude Protein (CP): Crude protein in the feed stuffs is estimated by determining the nitrogen
content of feed and multiplying it by a factor 6.25. Two assumptions are made in calculating the
protein content from the nitrogen: firstly, that all the nitrogen of the food is present as protein
and secondly that all food protein contains 16g N/100g. The nitrogen content of the food is then
expressed in term of crude protein (CP) calculated as follows. CP (g/100g) = g nitrogen /100g x
100/16 Or more commonly CP (g/100g) = g nitrogen /100g x 6.25
Both above assumptions are unsound. Different food proteins have different nitrogen contents,
and therefore different factors should be used in the conversion of nitrogen for individual food.
The nitrogen content of a number of common proteins together with appropriate nitrogen
conversion factor is shown as:
Food protein Nitrogen (g/lOOg) Conversion factor
Cotton seed 18.87 5.30
Soyabean 17.51 5.71
Barely 17.15 5.83
Oat 17.15 5.83
Wheat 17.15 5.83
Maize 16.00 6.25
Egg 16.00 6.25
Meat 16.00 6.25
Milk 15.68 6.38
1
, True Protein (TP): The term true protein is used to denote the protein only. It can be separated
from non-protein nitrogen by precipitation with cupric hydroxide or by heat coagulation. The
protein is then filtered and residue subjected to nitrogen estimation by Kjeldahl method. The
protein is determined by multiplied the factor 6.25.
Digestible Crude Protein (DCP): When the crude protein content of the feed stuffs is
multiplied by its digestibility coefficient, it gives the digestible crude protein. It is the most
common way of expressing the protein values and requirement of the ruminants on most of the
countries. In India, DCP is taken as the measure for expressing the protein values of feeds for
ruminants. Digestible crude protein figures are not entirely satisfactory assessments of protein,
because the efficiency with which the absorbed protein is used differs considerably from one
source to another.
Protein Equivalent (PE): In some of the European countries protein equivalent is used instead
of DCP. In protein equivalent non-protein nitrogen fraction is given half the nutritive of the true
protein and is calculated as follows:
PE= %DCP+ % DTP 2 So PE is the arithmetic mean of the percentage of DCP and DTP.
Protein Quality (PQ): In ruminants protein quality is not given much of the importance since all
the essential amino acids can be synthesized by microbs
Evaluation of Protem
Value of Feed in Animal Nutrition are synthesized in the rumen by the synthesis of microbial
proteins. However, digestible crude protein value for nonruminant animal is not adequate to
express the protein value. It is important to know how much of the absorbed protein is used by
the animal body. This utilization will be different with the various protein sources as it is
dependent upon the amino acid composition of the protein.
Evaluation of protein value of feed in non-ruminants:
Protein Efficiency Ratio (PER): The protein efficiency ratio normally uses growth of the rat as
a measure of the nutritive value of dietary protein. It is defined as the weight gain per unit weight
of protein eaten, and may be calculated by the following formula. . .. .)
Protem efficiency ratio = Gain in body weight (g )/'Protein consumed (g)
The PER values will vary with different protein sources as the composition of protein varies with
regard to essential amino acids. For the optimum rate of growth, various level of protein would
be required depending upon the quality. On this basis comparison between different sources of
protein can be made. It is simplest method for evaluating protein quality.
2
