Submitted to: International Journal of Poultry Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/1/2003
Publication Date: 11/1/2003
Citation: Corzo, A., Kidd, M.T., Kerr, B.J. 2003. Threonine need of growing female broilers. International Journal of Poultry Science. 2 (6): 367-371. Interpretive Summary: With the development of feed grade methionine, lysine, and threonine, flexibility towards a more balanced dietary protein level, while decreasing associated costs, has been achieved by nutritionists around the world. This has been convenient considering that these three amino acids are typically the most limiting in practical diets fed to broilers. Because threonine is typically the third limiting amino acid in broiler diets, research evaluating this amino acid has been relatively limited. Yet, understanding threonine in broiler feed formulation is critical in lowering dietary crude protein fed to broilers, and consequently, in reducing the amount of nitrogen excreted into the environment from broiler operations. Experimentation indicated that birds, fed a basal diet composed in part by peanut meal, would perform similar to birds fed a typically formulated diet, provided the peanut meal-based diet was fortified with crystalline threonine. The current experiments demonstrated that the threonine requirement estimates extrapolated from live performance and carcass measurements for birds from 30 to 42 days of age were equal to higher than previously reported in the 1994 National Research Council, Nutrient Requirements of Poultry. As environmental issues with nitrogen losses from livestock operations becomes more pressing and as the availability of crystalline amino acids becomes more economically viable, understanding amino acid limitations in low crude protein diets and their desired concentration in feeding programs for optimal production (performance and carcass composition) and minimal nitrogen excretion, is paramount to the broiler industry. Research results described in this report provide nutritionists at universities, feed companies, and broiler production units vital data on how to clearly define the isoleucine needs of broilers to properly formulate their diets to optimize growth performance and ultimately to minimize nitrogen excretion.
Technical Abstract: A study was conducted to evaluate Thr responses in female broilers from 30 to 42 days of age. Commercial Ross x Ross 508 females were randomly placed into battery cages. A test diet was formulated to provide 0.55% total Thr; progressive increments of 0.05% Thr at the expense of a filler created the experimental diets, up to 0.80% Thr. A conventional-type control diet (0.70% total Thr) was formulated to validate the titration diet which was composed in part by peanut meal, which was necessary to generate a Thr deficiency. Performance of birds fed the control diet was similar (P < 0.05) to the titration diet containing equal Thr (0.70%). Deficiency effects of Thr were seen for most variables. Furthermore, linear or quadratic responses occurred for most parameters measured. Optimization of dietary Thr was feasibly calculated for body weight gain and feed conversion, reaching dietary optimums (95% of the asymptote) at 0.69 and 0.71%, respectively. Carcass as well as breast meat improved in a linear manner with increasing dietary Thr. A hypothetical sigmoidal response exhibited by plasma Thr is in close agreement with the Thr requirements extrapolated from live performance measurements. Threonine response estimates obtained in present experimentation are equal to or higher than those previously reported, perhaps as a consequence of the environment to which the birds were exposed to, possibly translating into modifications of associated maintenance and growth requirements for Thr. However, values obtained for the 30 to 42 day-time period are in close agreement with current NRC (1994) recommendations from 21 to 42 days of age.