Effects of Different Dietary Ideal Protein Levels on Male and Female Broiler
Performance During Different Phases of Life: Single Phase Effects,
Carryover Effects, and Interactions Between Phases
P. J. A. Wijtten,*
A. Lemme,† and D. J. Langhout*
*Provimi B.V., Rotterdam, The Netherlands; and †Degussa AG, Feed Additives Applied Technology, Hanau, Germany
Several experiments in which the dietary
ideal protein (IP) levels were increased indicate that with
current IP recommendations the maximum performance
of broilers will not be achieved. However, available data
of this IP-increment approach is scarce and, for the starter
phase, entirely lacking. The objective of the present study,
therefore, was to generate data regarding the effects in
the starter phase and to test the impact of adequate vs.
high IP levels in preceding phases on the response to IP
increment in the phase under study. To evaluate this,
an IP dose response in the starter phase and factorial
arrangements combining adequate or high IP levels in
starter and grower diets with low, adequate, or high IP
levels in finisher diets were carried out with male and
: broiler, ideal protein, sex, age, phase)
2004 Poultry Science 83:2005–2015
Besides energy, amino acids (AA) are the most critical
dietary factors determining feed costs and performance
in the broiler industry. Therefore, it is of considerable
financial importance to continuously increase our knowl-
edge of broiler requirements for AA.
In the 1950s, Almquist (1952) established that growth
rate depends on the intake of the first limiting (indispens-
able) AA. Animal performance, furthermore, improves
in response to supplementation of that AA in the diet up
to the level that the second indispensable AA becomes
limiting. This theory has been fully accepted and is used
in feed formulation practice.
It is understood that requirements of poultry for AA are
influenced by dietary, environmental, and genetic factors.
The ideal protein (IP) concept has been developed, in
which AA requirements are often expressed as ratio to
Lys, leading to an ideal AA profile in which all indispens-
able AA are equally limiting. This approach was first
2004 Poultry Science Association, Inc.
Received for publication April 27, 2004.
Accepted for publication August 29, 2004.
To whom correspondence should be addressed: pwijtten@nl.
female broilers. Enhanced dietary IP levels in the starter
diet increased BW gain in the starter phase and in the
consecutive grower phase. Moreover, it was shown that
a delay in BW gain due to suboptimal IP levels in the
starter diet could only be partly compensated for in later
phases of life. These results demonstrate the need for a
reevaluation of IP levels used in practical starter diets.
Feed conversion efficiency and BW gain responses to in-