Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2004
Publication Date: 8/15/2004
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: Growth and tissue accretion rates of commercial broiler strains differ and the efficient utilization of lysine, the most costly amino acid in poultry diets, is dependent on adequate levels of a second amino acid, threonine. Excess levels of crude protein or specific amino acids in commercial poultry diets ultimately impact ammonia production and, of course, feed costs. Therefore, determination of the optimal ratio of threonine to lysine in poultry diets fed to the 8.2 billion broilers produced each year in the U.S. has both economic and environmental impact. The results of this study show that for 21 to 42 days of age, broiler chicken strains currently used by the U.S. commercial poultry industry require a diet having an optimal threonine to lysine ratio of 0.68%.
Technical Abstract: Broilers consuming diets marginal in Thr (threonine) may result in dietary Lys (lysine) being used inefficiently as well as causing reduced performance and breast meat deposition. Because the growth and tissue accretions rates for commercial broilers differ, the Thr needs in the three commercial broiler strains (A, multipurpose; B, high-yield; C, high-yield) known to differ in terms of feed intake, growth rate, and breast yield were evaluated. 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 (3x6 factorial) were replicated either 5 or 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) was maintained on a corn and soybean meal diet containing surfeit Thr (0.73% of diet). Birds fed the corn and soybean meal diet performed similar (P<0.05) to birds fed peanut meal diets with varying concentrations 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 abdominal 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 maximum response) of 0.74 and 0.71%, respectively, which are in close 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 was estimated as 0.74% total or 0.65% digestible equating to a Thr:Lys ratio of 0.68%.