Abstract
Optimal dietary methionine (Met) to lysine (Lys) ratio in presence of elevated dietary cysteine (Cys) levels was derived for meat type growing chicken. Twelve averaged weighed Ross 308 birds (each 50% of male and female per dietary treatment) were utilized in N balance trials. During starter (d10 - 20) and grower period (d25 - 35) five dietary treatments were used. Diets based on uniform mixtures of maize, wheat, soybean meal, potato protein and fish meal were supplemented with crystalline amino acids (AA). In diets 1 - 3, the dietary Cys to Met ratio was set as 85, 95 and 105 to 100, respectively. Diet 4, at a Cys to Met ratio of 105 to 100, was additionally supplemented with betaine (BET) as methyl group donor. Diets 1 - 4 were limiting in Met, diet 5 without L-Lys·HCl addition was limiting in Lys. Individual N-balance data per treatment were utilized for assessing protein quality and efficiency of dietary Met (Diets 1 - 4) or Lys (Diet 5) based on “Goettingen approach”. Elevated dietary Cys supply and supplemented BET failed to improve both dietary protein quality and Met efficiency. The established optimal Met to Lys ratio was on average 34 to 100 for growing chicken during starter and grower period, respectively.
Highlights
In a series of experiments the application of ideal protein concepts provided a considerable impact on efficacy of protein utilization, growth performance and carcass yields in growing chicken [1]-[8] and recommendations are available about the expected ideal amino acid ratio (IAAR) in diets of meat type chicken as summarized by Wecke and Liebert [8]
The results during the starter period indicate no pronounced effect on protein utilization when the Cys to Met ratio in Met limiting diets varied between 85 and 105 to 100
The reported studies based on data evaluation by “Goettingen approach” demonstrate, that elevated Cys supply between 85 and 105 percent of Met supply failed to improve both dietary protein quality and Met efficiency in starter diets for meat type chicken
Summary
In a series of experiments the application of ideal protein concepts provided a considerable impact on efficacy of protein utilization, growth performance and carcass yields in growing chicken [1]-[8] and recommendations are available about the expected ideal amino acid ratio (IAAR) in diets of meat type chicken as summarized by Wecke and Liebert [8]. Based on 24 reports, Wecke and Liebert [8] summarized 74 ± 2 to 100 as optimal SAA to Lys ratio, whereby 40 ± 4 to 100 counted as optimal for Met to Lys. Based on 24 reports, Wecke and Liebert [8] summarized 74 ± 2 to 100 as optimal SAA to Lys ratio, whereby 40 ± 4 to 100 counted as optimal for Met to Lys Actual studies assessing these IAARs and taking into account varying dietary Cys supply are scarce and inconclusive. It is indicated by Dilger and Baker [24] and observations of Liebert et al [25] that dietary Cys concentration has influence on efficiency of Met utilization in chicks. Several betaine (BET) supplementation studies provide support for this assumption [26]-[30]
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