Optimal in‐feed amino acid ratio for broiler breeder hens based on deletion studies

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The modern broiler breeder hens have a high potential to produce hatching eggs while maintaining the growth potential as the modern broilers (Richards et al., 2010). To take advantages of the full potential of these broilers breeder hens, it is necessary to ensure that the correct amount of protein and other nutrients is being provided (Lopez and Leeson, 1995). The proper control of the daily protein intake is needed due to the impacts on body composition and egg size in the laying phase (Joseph et al., 2000). Also, the utilization efficiency of the dietary protein is determined by the amino acid (AA) composition and the AA balance in relation to the broiler breeder hens’ requirements (Lopez and Leeson, 1995). For that reason, it is necessary to determine the AA requirements accounting for the physiological changes and provide the correct amount of AA to fulfil the maintenance requirements, support growth and meet the requirements for egg mass production (Fisher and Gous, 2009).
The current procedures to determine the AA requirements and their optimal balance utilize dose–response studies making use of graded AA supplementation (Baker et al., 2002; Baker, 2003), which the diets are formulated to meet the recommendations from NRC (1994), except for the AA under study. Estimates of the AA requirement are derived by the first intersection of the quadratic response curve with the plateau from broken‐line analysis, which is used in the conclusion of the optimal dietary AA ratios. However, this procedure is expensive and time‐consuming because multiple assays are needed (Rollin et al., 2003; Dorigam et al., 2015). On the other hand, it is possible to derive the optimal AA ratios from the responses obtained with the individual AA deletion of an AA balanced diet in only one assay (Wang and Fuller, 1989). This balanced diet is supplemented with industrial AA to strictly meet the AA requirements of the animal, and then, the AA under study is individually deleted from the balanced diet. Both responses with the balanced and the deleted diets are measured, and the observed slope of the response criteria between these diets was utilized for conclusion of optimal dietary ratios between individual AA. The concepts of this approach are applied in the current study. However, as concluded in the previous study with broilers (Dorigam et al., 2015), it seems that this approach produces results with higher variation in the estimates and in part this occurred because the maintenance requirement, feather losses and the nitrogen deposition in the different tissues were not measured separately in the estimates of the AA requirements. The new hypothesis presented in this study suggests that the partition of the nitrogen retention may contribute to decrease this variation and produce more reliable results. Thus, the aim of this study was to apply the deletion method to derive an ideal amino acid ratio (IAAR) for broiler breeder hens based on the partition of the nitrogen retention.
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