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Metabolism and Nutrition, Amino Acids

Excessive amounts of dietary protein, i .e ., nitrogen, cannot be stored into the organism as reserve, which inevitably leads to its excretion in environment in metabolic processes that require unnecessary energy expenditure . Establishing poultry requirements for essential amino acid is a crucial step to reduce excessive dietary crude protein supply and hence approach the amount of amino acids provided by diets to bird nutritional needs . From the 70s of the last century onward, no studies were conducted with the purpose of establishing Japanese quail requirements for leucine (Leu), whose excessive concentration in diets may lead to valine and isoleucine catabolism in liver, which may reflect in changes in feed intake behavior and performance trait impairments . To determine Japanese quail requirements for Leu, a total of 280 28-weekold Japanese quails were randomly assigned to 8 treatments with 7 replicates of 5 quails . Dilution technique was used to produce the levels of 3 .92, 7 .05, 10 .2, 13 .3, 15 .7, 17 .2 and 18 .8g Leu/kg diet . The 8thtreatment consisted of a control diet to confirm whether Leu was indeed the 1st limiting amino acid in experimental diets . Such diet was produced supplementing 3 .16g L-Leu/kg diet in the diet with the lowest level of Leu (3.92mg/kg) to achieve the second lowest level (7.05mg/kg). All performance data collected in the last 4 weeks of the 10-week feeding trial was used to estimate quail requirements . Data were analyzed as one-way ANOVA and Leu requirement estimated using linear brokenline (BL) and quadratic-broken-line (QBL) regression models, where performance traits were regressed against daily Leu intake . Quails fed control diet exhibited improvements in overall performance compared with those fed the lowest Leu level, which proves that Leu was the 1st limiting amino acid in diets . The breakpoint in egg production was observed at 230 and 310mg Leu/bird/day, according to BL and QBL models . Linear broken-line and QBL models estimated maximum egg weight at 267 and 396mg Leu/bird/day, respectively . Quails fed increasing Leu levels had the egg output (EO) optimized at 246 and 345mg Leu/bird/day according to BL and QBL, respectively . Irrespective of the performance trait assessed, the smallest AIC values were observed for QBL model, which indicates that data fitted better to this model. Based on the EO outcomes, Japanese quail requirements for Leu in the egg-laying phase is 345 mg/bird/day . Acknowledgements: The authors thank FAPESP (2013/25761-4 and 2017/12182-7) for the financial support and Ajinomoto and Evonik for the crystalline amino acids and analysis .