Submitted to: Poultry Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/18/2004
Publication Date: 8/1/2004
Citation: Kidd, M.T., Corzo, A., Hoehler, D., Kerr, B.J., Barber, S.J., Branton, S.L. 2004. Threonine needs for broiler chickens with different growth rates. Poultry Science. 83: 1368-1375. Interpretive Summary: Dietary amino acid concentration in the diet should closely meet maintenance and tissue accretion needs of commercial broilers. This is especially important toward the middle and end of the rearing period of the bird when bird growth and muscle development is at its maximum. However, because diets are formulated with ingredients that do not match the nutrient needs of the bird exactly, under- and over-formulation of amino acids may exist and cause a depression in broiler performance and consequently, increase the excretion of nitrogen into the environment. The nutrient threonine is of critical importance as it is costly in dietary formulations, its deficiency will decrease the efficiency of sulfur amino acid and lysine utilization, and threonine is typically the third limiting amino acid behind methionine and lysine in commercial broiler diets. Experimentation indicated that birds from 21 to 42 days of age required approximately 0.74% total dietary threonine to optimize body weight gain and breast meat yield. This relates to a threonine to lysine ratio of 0.65 on a digestible amino acid basis. Across strains of birds with different growth rates, the optimal dietary threonine to lysine ratio did not vary greatly and should be considered in dietary formulations for optimal bird performance. In addition, as environmental issues with nitrogen losses from poultry operations becomes more pressing and as the availability of crystalline amino acids becomes more economically viable, understanding threonine concentration in feeding programs for optimal production and minimal nitrogen excretion is paramount to the broiler industry. Research results described in this report provides nutritionists at universities, feed companies, and broiler production facilities vital data on the importance of threonine in dietary formulations.
Technical Abstract: Broilers consuming diets marginal in Thr may result in Lys inefficiency, in turn reducing breast meat because Thr is third limiting. Because the growth and tissue accretion rates of commercial broilers differ, a study evaluated Thr needs in three commercial broiler strains (A, multipurpose; B, high-yield; C, high-yield) known to differ in terms of feed intake, growth rate, and breast meat yield. Birds were randomized across 96 floor pens (12 birds/pen), received a common diet from d 1 to 20, and fed graduations of Thr (0.52 to 0.87% total Thr in 0.07% increments) from d 21 to 42. Treatments (3 x 6 factorial) were replicated between 5 and 6 times. The corn, soybean meal, and peanut meal test diet contained 0.43% and 0.96% digestible Thr and Lys, respectively. An additional group of strain C birds (8 pens) were maintained on a corn and soybean meal diet containing surfeit Thr (0.73% of diet). Birds fed to corn and soybean meal diet performed similar (P < 0.05) to birds fed to peanut meal diets with varying levels of Thr. A feed conversion interaction (P < 0.05) occurred indicating that strain C was more sensitive to Thr deficiency than strains A and B. The abdominal fat interaction (P < 0.05) indicated that strain A had more relative fat than strains B and C. All strains differed (P < 0.05) in terms of BW gain (A, 78.2; B, 75.1; C, 72.9 g/d). Strain C had the lowest (P < 0.05) feed intake resulting in the lowest (P < 0.05) Thr intake, but it had the highest (P < 0.05) breast meat yield. Most parameters tested yielded quadratic (P < 0.05) models whereby Thr estimates could be predicted. Namely, BW gain and breast meat yield resulted in total Thr estimates (95% of the upper asymptote) of 0.74 and 0.71%, respectively, which are in good agreement with the 1994 NRC (0.74%). The plasma Thr sigmoid response verified the former estimates. Analysis of strain intercepts and slopes as affected by Thr differed (P < 0.05) in terms of feed intake, but not BW gain or breast meat yield. The 21 to 42 d Thr need across strains is about 0.74% total or 0.65% digestible (Thr/Lys of 0.68).