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.

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 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 increased IP levels in the grower and finisher diets were less pronounced when high compared with adequate IP levels were fed in the preceding phase. This difference in response could not be detected statistically but was consistent between experiments and phases. Therefore, this phenomenon should not simply be neglected.