Abstract
The objective of this study was to determine the ideal digestible tryptophan:digestible lysine ratio in diets for laying hens from 24 to 40 weeks of age. Two hundred and forty Hy-Line W-36 laying hens at 24 weeks of age were distributed in a completely randomized design, with five treatments, eight replicates and six birds per experimental unit. The digestible tryptophan levels in the experimental diets were 1.57; 1.68; 1.79; 1.90 and 2.01 g/kg, providing ratios of digestible tryptophan:digestible lysine of 0.215; 0.230; 0.245; 0.260 and 0.275. The increase in the levels of digestible tryptophan in the diet linearly improved the feed intake, digestible tryptophan intake, digestible lysine intake, egg production, egg mass, feed conversion per egg mass and utilization efficiency of digestible lysine for eggs mass. There were quadratic effects from the digestible tryptophan levels on egg weight. For the efficiency of utilization of digestible lysine for egg mass, there was better adjustment of the data to the LRP model. The level of digestible tryptophan in the diet from which the plateau occurred was 0.184%. This level corresponded to the intake of 142 mg/bird/day of digestible tryptophan and digestible tryptophan:digestible lysine ratio of 0.252. The ideal digestible tryptophan:digestible lysine ratio recommended in diets for laying hens from 24 to 40 weeks of age is 0.252 (25.2%).
Highlights
Modern laying hens are able to achieve high indexes of productivity
When completing 24 weeks of age, birds were subjected to experimental treatments that consisted of diets with the same amount of nutrients, except for the levels of digestible tryptophan
The suboptimal level was important to ensure that all digestible lysine consumed was used and that the digestible tryptophan:digestible lysine ratio estimated reflected the real needs of birds
Summary
For this, it is essential that they receive diets with adequate levels of amino acids. Besides the components of body and egg proteins, the amino acids are precursors of specialized products important in the metabolism. A milestone in the nutrition of monogastrics was the application of the concept of ideal protein in diet formulations. This allowed a better balance of amino acids in the diets and a better fulfillment of requirements of the birds. Studies with amino acids should be focused on the establishment of ideal ratios between the essential amino acid and lysine, in which it is important to evaluate to which extent the industrial amino acids can be added to the diets, considering productive, environmental and economic aspects
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