ABSTRACT
1. A feeding trial was conducted to measure the responses of Japanese quail to dietary valine. In total, 280 Japanese quail were randomly assigned to eight treatments giving seven replicates (cage - 35 cm length, 35 cm width × 15 cm high). Experimental diets were formulated using a dilution technique to give a range dietary Val concentration (1.97 to 9.85 g/kg).2. Feed intake was maximised at 6.66 g Val/kg and above, but declined linearly below this level. Body weight reached a maximum of 170 g on 6.66 g Val/kg. Egg output peaked at 9.5 ± 0.3 g/bird/d with an egg weight of 11 g for the 6.66 g Val/kg diet. Rate of laying for the group that received the feed with the lowest Val content was close to zero (1.40%), but egg weight on this treatment was 70% of the maximum egg weight. Valine required per gram of egg output was estimated as 10.6 mg/g, whereas the maintenance requirement was 159 mg/kg body weight. Val required for maximum egg output was estimated in 154 mg/d.3. The marginal cost of Val in Brazil currently is negative below a level of 8.0 g/kg feed, which is above that required for maximum egg output. Consequently, Val cannot be regarded as a limiting amino acid currently, as the optimum economic intake exceeds the requirements of all the individuals in the population. The price of a quail egg weighing 11 g in Brazil at the time of the experiment was R$ 0.021. Even if the marginal revenue for these eggs was doubled to 0.4 c/g, there would be no reason to increase the intake of Val.