Digestible isoleucine requirements for Japanese quails in laying phase

Using inadequate levels of isoleucine (Ile) can induce a lower egg mass (EM) production
in quails, because the Ile deficiency results in protein synthesis limitation when unused
excess of amino acids results in more energy used to support nitrogen excretion. Thus,
the aim of this study was to determine the requirements of Ile for EM production in
Japanese quails using the broken-line model. For this trial, 280 Japanese quails with 25
weeks of age were distributed in a completely randomized design with eight treatments,
seven replicates and five birds each. The experimental diets were formulated using the
dilution technique. A high protein diet containing approximately 1.2 times the Ile
requirement and 1.4 times the requirements of other essential amino acids, the diets was
formulated based on the recommendations in the Brazilian Tables. This diet was
sequentially diluted with a protein-free diet, isocaloric, thereby generating the
experimental treatments with different levels of Ile. The treatments consisted of seven
diets with increasing levels of Ile (1.7, 3.03, 4.42, 5.77, 6.79, 7.47 and 8.15 g/kg of
digestible Ile and a control diet with 1.7 g/kg + 1.33 g/kg of L-isoleucine used to verify
if the responses are due to the limitation of Ile in the protein profile). The trial lasted seven
weeks, with three weeks for adaptation and four weeks of data collection. The EM data
was subjected to analysis of variance, considering 5% of significance, and then used in
the adjustment of the broken-line model using a statistical software (SAS 9.2 software).
The broken-line model was adjusted considering the Ile intake as the independent variable
and EM as the dependent variable: Y = Rmax + U * (R-X); where Y is the EM (g/day),
Rmax is the maximum EM response (g/day); U is the Slope; and R is the optimal Ile intake
(mg/day) for maximum EM response. The broken line model obtained was: Y = 9.17 -
0.0817 * (123.6-X). This result indicate that the optimal Ile intake is 123.6 mg/day for a
maximum EM of 9.17 g/day,leading to conclude that quails have a requirement of 123.6
mg/day of digestible Ile for optimum EM and considering a feed intake of 25 g/day, is
obtained the dietary Ile concentration of 4.94 g/kg for quails in the laying phase.