Abstract
The objective of this study was to evaluate the requirement of digestible tryptophan for white laying hens in the production stage fed diets of different digestible tryptophan:digestible lysine ratios, as well as animal performance and histological alterations in their reproductive and digestive systems. A total of 280 white laying hens at 29 weeks of age were distributed in a completely randomized design with five treatments and seven replications with eight birds in each. The treatments consisted of a base feed, formulated with corn, soybean meal and corn gluten meal, and supplemented with the synthetic amino acids L-lysine, DL-methionine, L-threonine, L-isoleucine, L-arginine, and L-valine, so as to meet the nutritional requirements for laying hens, except for digestible tryptophan. The basal diet was supplemented with 0.00; 0.017; 0.035; 0.052; and 0.069 g/kg of L-tryptophan in substitution for corn starch with the objective of reaching the levels of 0.151; 0.167; 0.183; 0.199; and 0.215 g/kg of digestible tryptophan in the feed. For the ratio between digestible amino acids and lysine, the recommendation of Brazilian Tables for Poultry and Swine was followed, except for the digestible tryptophan:digestible lysine ratios, which were 19, 21, 23, 25 and 27 for each treatment. The variation in the digestible tryptophan:digestible lysine ratio promoted changes in performance and in the histological characteristics, improving the results. The digestible tryptophan:digestible lysine ratio of 24.5% in the feed of white laying hens in production stage promotes better animal performance and histological results.
Highlights
According to Peganova & Eder (2003) and Deponti et al (2007), tryptophan is significant in the formulation of feeds with a reduced content of protein in the nutrition of laying hens because it is considered the third limiting amino acid
Tryptophan is the forerunner of serotonin and melatonin syntheses, and reduces aggressiveness in birds, which, with no doubt, eases the daily management of the birds and, in a way, contributes to a more efficient egg production, since the number of damaged eggs is reduced in this situation
Tryptophan deficiency provokes a reduction in feed intake (Peganova & Eder, 2002) and its requirement can be influenced by long-chain neutral amino acids present in the diet of laying hens, such as isoleucine, valine, leucine, phenylalanine, tyrosine, methionine and histidine, and even more by the protein in the diet
Summary
According to Peganova & Eder (2003) and Deponti et al (2007), tryptophan is significant in the formulation of feeds with a reduced content of protein in the nutrition of laying hens because it is considered the third limiting amino acid. L-tryptophan 98% is produced by the fermentation of raw materials of agricultural origin, such as beet molasses or hydrolyzed starch. It consists of white and light yellow crystals with 98% tryptophan and 100% digestibility (Ajinomoto, 2010). Tryptophan deficiency provokes a reduction in feed intake (Peganova & Eder, 2002) and its requirement can be influenced by long-chain neutral amino acids present in the diet of laying hens, such as isoleucine, valine, leucine, phenylalanine, tyrosine, methionine and histidine, and even more by the protein in the diet. For birds in the laying stage, the recommendations are very diverse
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