Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/1/2011
Publication Date: 4/3/2012
Citation: Quant, A.D., Lindemann, M., Kerr, B.J., Payne, R.L., Cromwell, G.L. 2012. Standardized ileal digestible tryptophan to lysine ratios in growing pigs fed corn-based and non-corn-based diets. Journal of Animal Science. 90:1270-1279. Interpretive Summary: Optimum amino acid intake is important to maximize growth and feed efficiency in pigs. Although there has been a large amount of research conducted on the lysine requirement in pigs, there has been limited research conducted on the total or true tryptophan requirement. Providing optimal tryptophan concentrations in diets fed to pigs will not only optimize animal performance, but because environmental issues with nitrogen losses from swine operations, understanding tryptophan limitations in low crude protein diets is paramount. Based on data obtained in these experiments, the optimum standardized ileal digestible tryptophan:lysine ratio is 15.7% and appears to be unaffected by the dietary feedstuffs used as long as the diets are formulated on an standardized amino acid basis. Research results described in this report provides nutritionists at universities, feed companies, allied industries, and swine production facilities data on how to define the tryptophan needs of pigs to formulate diets necessary to optimize growth performance and subsequently minimize nitrogen losses into the environment.
Technical Abstract: Two 21-d experiments were conducted to determine the optimum standard ileal digestible (SID) Trp:Lys ratio in growing pigs fed corn-based diets compared to non-corn-based diets. The primary response variables in both experiments were ADG and plasma urea N (PUN) concentrations with the optimum SID Trp:Lys ratio determined using broken-line analysis. Experiment 1 evaluated the optimum SID Trp:Lys ratio in growing pigs fed corn-based diets consisting primarily of corn but using some Canadian field peas and corn gluten meal to keep the SID Trp:Lys ratio low. This experiment utilized 120 crossbred pigs (initial BW: 25.78 ± 2.47 kg) that were blocked by gender and initial BW and allotted to 5 SID Trp:Lys ratios with 5 pigs/pen. Dietary treatments were formulated by the addition of supplemental Trp to create various SID Trp:Lys ratios (12.77, 14.07, 15.50, 16.91, and 17.94%) with a constant SID Lys level of 0.66%. As the SID Trp:Lys increased from 12.77 to 17.94%, ADG increased (0.562, 0.648, 0.788, 0.787, and 0.815 kg/d) linearly (P < 0.001) and quadratically (P = 0.009), resulting in an optimum SID Trp:Lys ratio of 15.73% (P < 0.001). Plasma urea N decreased (10.43, 9.30, 8.21, 8.55, and 9.25 mg/dL) linearly (P = 0.069) and quadratically (P = 0.015) resulting in an optimum SID Trp:Lys ratio of 15.83% (P = 0.007). Experiment 2 evaluated the optimum SID Trp:Lys ratio in growing pigs fed non-corn-based diets consisting primarily of barley and Canadian field peas, with smaller proportions of corn and wheat. Experiment 2 utilized 120 crossbred pigs (initial BW: 28.49 ± 2.92 kg) that were allotted to 5 increasing SID Trp:Lys ratios (13.05, 14.32, 15.59, 16.85, and 18.11%; 0.66% SID Lys) in the same manner as Exp. 1. As SID Trp:Lys ratios increased in Exp. 2, ADG increased linearly (P = 0.007) with the optimum SID Trp:Lys ratio of 15.99% (P = 0.048). Plasma urea N concentrations decreased linearly (P = 0.056) and quadradically (P = 0.067) as SID Trp:Lys ratios increased, resulting in an optimum SID Trp:Lys ratio of 15.29% (P = 0.009). Averaging the break point values for ADG and PUN obtained from broken-line analysis for Exp. 1 and 2 produced optimum SID Trp:Lys ratios of 15.78 and 15.64%, respectively. Based on the results from these 2 experiments, it appears that the optimum SID Trp:Lys ratio is virtually unaffected by the dietary feedstuffs used as long as the diets are formulated on an SID AA basis.