Threonine and crude protein responses in broiler chicks

A (2 x 3) factorial arrangement of treatments was used in one experiment to evaluate dietary crude protein (CP) (190 and 225 g/kg) and dietary Thr (6. 0, 7.0 and 8.0 g/kg) in Ross x Ross 308 male broilers from Days 5 to 15. At Day 5,336 chicks were randomized across 48 battery pens (seven chicks per replicate and eight replicates per treatment). Essential amino acids, excep t Thr, were in excess of [National Research Council, 1994. Nutrient Require ments of Poultry, 9th Edition (revised). National Academy Press, Washington , DC] specifications and similar between both CP diets. Chicks receiving th e 190 g CP/kg diet had increased (P < 0.001) body weight (BW) gain and feed intake compared with chicks fed the 225 g CP/kg diet. Protein efficiency r atio was improved (P < 0.001) in chicks fed the 190 g CP/kg diet versus chi cks fed the 225 g CP/kg diet. Similarly, chicks fed the 190 g CP/kg diet ha d reduced nitrogen excretion (P = 0.043) in comparison with chicks receivin g the 225 g CP/kg diet. Increasing dietary Thr from 6.0 to 7.0 g/kg diet im proved (P < 0.001) BW gain and feed intake. Immune organ weights were not a ffected by dietary treatments. Feed:gain ratio was improved (P = 0.016) in chicks receiving both CP diets as Thr was increased from 6.0 to 7.0 g/kg di et. However, chicks fed 8.0 g Thr/kg diet had lower (P = 0.016) feed:gain r atio when fed the 225 g CP/kg diet than chicks fed the 190 g CP/kg diet. Ma le broiler chicks had improved growth performance measurements when fed 7.0 g Thr/kg diet. The effect of CP on Thr needs of chicks should be studied f urther. (C) 2001 Elsevier Science B.V. All rights reserved.