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Optimal tryptophan: lysine Ratio for 25-40 Kg Growing Pigs Fed Diets Containing 35 % Distillers Dried Grains with Solubles

Published on: 3/11/2021
Author/s : Author: J. Caroline González-Vega – Evonik Operations GmbH. John K. Htoo, n/a – Evonik Operations GmbH. Maryane S. Sespere Faria Oliveira, Postdoctoral Research Associate, University of Illinois. Hans H. Stein, Professor, Department of Animal Sciences, University of Illinois.

Distillers dried grains with solubles (DDGS) has a high concentration of Leu, and the Trp requirement for growing pigs may be increased if diets contain excess Leu. Therefore, the objective of this experiment was to determine the optimum standardized ileal digestible (SID) Trp:Lys ratio in growing pigs fed diets with excess Leu from DDGS. A diet based on corn, soybean-meal, and 35% DDGS was formulated to be deficient in Trp and Lys, according to NRC requirements (0.13% SID Trp; 0.88% SID Lys; 15% SID Trp:Lys ratio). Four diets were prepared by adding L-Trp to the basal diet, which resulted in analyzed SID Trp:Lys ratios of  18, 20, 23, and 24% in these diets. One-hundred and twenty growing pigs (26.3 ± 2.0 kg) were allotted to one of the 5 dietary treatments with 3 pigs per pen and 8 pen replicates in a completely randomized design. Diets were fed for 21d and blood samples were collected on d-21. Data were analyzed by linear and quadratic contrasts in SAS. The optimal SID Trp:Lys ratio was estimated using linear broken-line (LBL) and quadratic broken-line (QBL) regressions for ADG and G:F, using NLIN procedure in SAS. Results indicated that average daily feed intake, ADG, G:F, and final body weight increased (linear and quadratic, P < 0.01) and plasma-urea-nitrogen decreased (linear and quadratic, P < 0.05) as dietary SID Trp:Lys increased (Table 1). The SID Trp:Lys ratio to optimize ADG was 20.9 and 23.4% by LBL and QBL, respectively. The G:F was optimized at 18.7 and 20.2% by LBL and QBL, respectively. The average SID Trp:Lys ratio for the 4 measurements was 20.8% which is greater than the current NRC requirement (SID 17.3%). In conclusion, diets formulated with 35% DDGS may need more dietary Trp than current NRC values.

Hans H. Stein is a professor of Animal Science at the University of Illinois, Urbana-Champaign, where he is conducting research and providing outreach programs in the area of intestinal physiology and feed ingredient evaluation. Previous jobs include positions as assistant and associate professor at South Dakota State University, jobs in the feed industry, and jobs in primary agricultural production. He obtained a PhD degree in monogastric nutrition from the University of Illinois, and a Masters degree from the Royal Veterinary and Agricultural University in Copenhagen, Denmark.
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