LAUSR

ABSTRACT Threonine (Thr), the third limiting amino acid in conventional poultry diets, plays a vital role in growth performance and immunocompetence of gastrointestinal tract and tissue protection. A dose-response experiment was conducted to estimate the Thr requirements of growing meat-type Japanese quail using growth performance parameters as response criteria and estimating the break-point as the minimum requirement by fitting different broken line models into the data. Five increments of Thr including 7.38, 8.38, 9.38, 10.38, and 11.38 g Thr/kg of diet were used from 7 to 21 days of age. in the second and third week of age. A total of 375, 7-day old quail chicks were randomly allotted to one of five experimental diets each with 5 replicate pens each and 15 birds per pen. Feed intake (FI), weight gain (WG), feed conversion ratio (FCR), dressing (DRS), breast meat yield (BMY), thigh meat yield (TMY), and relative weight of bursa of Fabricius (BURS) were measured and used to fit regression models. Depending on different broken line models, the Thr requirements for optimum WG, FCR, TMY, DRS, and BURS ranged from 8.68 to 11.36, 10.25 to 10.38, 7.35 to 8.05, 10.16 to 10.33, and 9.38 to 10.71 g/kg of diet, respectively. The highest required amount of Thr was for WG (11.36 g/kg) followed by BURS (10.71 g/kg) and FCR (10.38 g/kg) using broken line models. Desirability function analysis for performance estimated the maximum WG and lowest FCR at 11.38 g Thr/kg of diet. Principal component analysis showed that FCR had the highest correlation with dietary Thr followed by WG. The moderate high eigenvalue of BURS provides evidence for immunocompetence contribution of dietary Thr in growing quail. Based on this experiment, the higher levels of Thr titrations may be needed than 11.38 g/kg to fit spline models. Overall, the estimated Thr by desirability function would be more reliable estimation than those estimated by broken line models.