Threonine and crude protein responses in broiler chicks

A (2×3) 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×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, except Thr, were in excess of [National Research Council, 1994. Nutrient Requirements of Poultry, 9th Edition (revised). National Academy Press, Washington, DC] specifications and similar between both CP diets. Chicks receiving the 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 ratio was improved (P<0.001) in chicks fed the 190 g CP/kg diet versus chicks fed the 225 g CP/kg diet. Similarly, chicks fed the 190 g CP/kg diet had reduced nitrogen excretion (P=0.043) in comparison with chicks receiving the 225 g CP/kg diet. Increasing dietary Thr from 6.0 to 7.0 g/kg diet improved (P<0.001) BW gain and feed intake. Immune organ weights were not affected 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 diet. However, chicks fed 8.0 g Thr/kg diet had lower (P=0.016) feed:gain ratio when fed the 225 g CP/kg diet than chicks fed the 190 g CP/kg diet. Male 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 further.