Submitted to: Animal Feed Science And Technology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/17/2004
Publication Date: 7/20/2005
Citation: Guzik, A.C., Pettitt, M.J., Biltranena, E., Southern, L.L., Kerr, B.J. 2005. Dietary threonine:lysine and tryptophan:lysine ratios of nursery pigs. Animal Feed Science And Technology. 89:297-302. Interpretive Summary: Optimum amino acid balance is important to maximize growth and efficiency in pigs. Diets are routinely formulated to meet the lysine requirement, and then ratios of the other amino acids are used to provide amino acids close to or at the requirement for maximum performance with a minimum excess of amino acids. There has been numerous research conducted on the lysine requirement in all phases of growth including nursery pigs, however, there has been limited research conducted on the optimum true threonine and tryptophan ratios to lysine in nursery pigs. Providing optimal amino acids ratios for threonine and tryptophan could enhance performance in nursery pigs. Based on a true digestible amino acid ratio basis, the National Research Council Subcommittee on Swine Nutrition (1998) suggests a ratio of threonine:lysine of 0.62 and a ratio of tryptophan:lysine of 0.18 in pigs 5 to 10 kg and 10 to 20 kg. Variation in requirements published in the literature demonstrates the need for a more accurate estimation of the threonine and tryptophan requirement and their ratios relative to lysine that is necessary for maximum growth performance. In addition, evaluation of potential interactions between tryptophan:lysine and threonine:lysine ratios in nursery pigs will improve the ability to optimally formulate nursery pig diets. Overall, optimal performance was obtained in pigs fed the true digestible tryptophan:lysine ratio of 0.195 at threonine:lysine ratios 0.60 or 0.65. This suggests that a tryptophan:lysine ratio above that currently recommended may be needed to maximize performance in diets containing wheat and barley. Research results described in this report provides nutritionists at universities, feed companies, and swine production units vital data on how to clearly define the tryptophan:lysine and threonine:lysine ratios in starting pigs to properly formulate their diets to optimize growth performance and ultimately to minimize nitrogen excretion.
Technical Abstract: The optimal ratio of tryptophan (Trp):lysine (Lys) and threonine (Thr):Lys was studied in nursery pigs from 7.1 to 15.6 kg BW. Treatments were arranged in a 3 x 3 factorial with three calculated ratios of true digestible Thr:Lys (0.55, 0.60, or 0.65) and Trp:Lys (0.145, 0.170, or 0.195). Treatments were replicated with eight pens of four pigs each. The experiment lasted 28 d with Phase II (1.19% true digestible Lys, initially 24 d of age and 7.1 kg BW) and Phase III (1.01% true digestible Lys, initially 38 d of age and 9.8 kg BW) diets fed for 14 d each. Threonine by Trp interactions were observed for ADG during each period, and for daily feed intake during Phase III and overall. Generally, Trp addition linearly increased gain and feed intake at Thr:Lys of 0.60 and .065 but not at 0.55. Gain:feed was increased linearly (P < 0.01) with increasing levels of Trp during both growth periods. There were no main effects of Thr. Overall, optimal performance was obtained in pigs fed the true digestible Trp:Lys ratio of 0.195 at Thr:Lys ratios 0.60 or 0.65. These results indicate that Trp:Lys ratios above 0.19% may be needed to maximize performance in diets containing wheat and barley.