Feeding During The Production Period - Amino Acids Requirements

Genetic progress and nutritional consequences

Just as for the other species, genetic progress has a considerable influence on dietary amino acid concentrations. Over the last 30 years, production to a constant age has increased by more than 40 %, while feed consumption has been reduced by about 10 %. An important consequence of this genetic progress has been a change in the daily amino acid requirements. It has also called into question the practice of phase feeding, since productivity remains high over longer and longer periods. The best units nowadays have daily egg outputs of over 60g/bird right up to 52 weeks of age.

The implication of genetic change in deciding amino acid levels is, therefore, considerable. It can be approached in the following way:

Food conversion ratio over the period 30-50 weeks:

1971: 2.87 g of feed / g of egg
1981: 2.36 g of feed / g of egg
2005: 1.95 (-17%) g of feed / g of egg

Classically, daily requirements have been expressed in mg / day. While this type of expression may be very easy for the formulator to use, it does not allow for genetic progress, nor for genotypic differences. Those genotypes, which produce large eggs, have larger daily requirements than those, which produce small eggs.

Most Researchers agreed to express requirements in mg of amino acids per gramme of eggs produced. This method enables us to tackle the « requirement » starting from numerous experimental data sources. It is more precise. The synthesis that we have carried out according to this method shows it to be an excellent way of determining requirements.

Ideal protein and amino acids requirements

The concept of ideal proteins is a means of expressing the requirements for amino acids as a percentage of the requirement for LYS. There is a limited interest in applying this concept to layers. It implies that a balance between the different amino acids is necessary for optimizing requirements. That would suggest that high protein or amino acid levels would have a negative effect on performance.

In fact the formulator should make a point of satisfying the requirement for the following amino acids: MET - CYS - LYS - THR - TRP - ISO and VAL. This is only valid for diets and raw materials in common usage.

Those requirements, which need to be defined by comparison with reference tables, have been expressed from NRC (1994) table of raw materials composition. These results have been expressed as digestible amino acids by using the digestibility coefficients mentioned in the RPAN 1993 tables. Giving the expression in the digestible form has enabled to reduce the variability of the results observed.

Recommendations for amino acids expressed in total or digestible and ideal proteins established for a production of 59,5 g per day.



Feed formulation

Digestible Amino Acids: Bird requirements and formulation of diets should be made in terms of digestible amino acids. By formulating in digestible Amino Acids we are better able to satisfy the requirements of the birds, to reduce the necessary safety margins and assess the raw materials according to their true biological value. Formulation according to total amino acids leads to the same nutritional value being given to all raw materials irrespective of their digestibility. That leads naturally to increasing the safety margins in order to guarantee fully meeting the requirements of the birds.

Protein Requirements: When diets are formulated by taking into account the need to satisfy the requirement for each of the 7 essential amino acids, it doesn't seem to be necessary to introduce a minimal constraint for protein. The requirements for the limiting amino acids are generally enough.

On the other hand, if all the essential amino acids are not taken into account when formulating, it is necessary to use a constraint for minimum protein, so as to reduce the risk of a deficiency.

Limiting factors: The experience acquired during the last decades in the feeding of layers, especially the use of synthetic lysine, has enabled us to assert that ISOLEUCINE and VALINE are becoming the limiting factors in layers feeds when meat products are excluded from the feed or when they are used in formulae based on wheat.

TRYPTOPHAN is the limiting factor in formulae, where the base consists of maize, soybean meal and meat products.

THREONINE and still less ARGININE do not appear to be limiting in the diets used nowadays.

These last two amino acids need to be studied still further.

When the requirements for ISO, VAL and TRY are covered, the requirements for the other essential and non-essential amino acids are always satisfied when 300 mg of protein per gram of egg is supplied. When the feed formula takes into account the requirements ISOLEUCINE and VALINE, it is not necessary to impose a constraint for a minimum protein level.

Feed consumption and formulation:

The amino acid concentration of the diets, therefore, depends on:

- the potential of egg mass produced, which itself determines the daily requirements
- the daily feed consumption which determines the amino acid concentration
- the feed efficiency at peak of production given the amino acid concentration in dividing the requirement expressed in mg of amino acid by the Feed Conversion Ratio.