Standardized ileal digestible tryptophan-to-lysine ratios in growing pigs fed corn-based and non-corn-based diets.

ABSTRACT

Two 21-d experiments were conducted to determine the optimum standardized ileal digestible (SID) TrpLys in growing pigs fed corn-based diets compared with non-corn-based diets. The primary response variables in both experiments were ADG and plasma urea N (PUN) concentrations with the optimum SID TrpLys determined using broken-line analysis. Experiment 1 evaluated the optimum SID TrpLys in growing pigs fed corn-based diets consisting primarily of corn with minor inclusion of Canadian field peas and corn gluten meal to keep the SID TrpLys low. This experiment used 120 crossbred pigs (initial BW 25.73 ± 2.46 kg) that were blocked by sex and initial BW and allotted to 5 SID TrpLys with 5 pens each for the first 4 treatments and 4 pens for the last treatment and 5 pigs/pen. Diets were formulated by the addition of supplemental Trp to create various SID TrpLys (12.77, 14.07, 15.50, 16.91, and 17.94%) with a constant SID Lys of 0.66%, which was determined to be 83% of the Lys requirement for pigs at this location. As the SID TrpLys 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 TrpLys 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 TrpLys of 15.83% (P = 0.007). Experiment 2 evaluated the optimum SID TrpLys 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 used 120 crossbred pigs (initial BW 28.49 ± 2.92 kg) that were allotted to 5 increasing SID TrpLys (13.05, 14.32, 15.59, 16.85, and 18.11%; 0.66% SID Lys) in the same manner as Exp. 1. As SID TrpLys increased in Exp. 2, ADG increased linearly (P = 0.007) with the optimum SID TrpLys of 15.99% (P = 0.048). Plasma urea N concentrations decreased linearly (P = 0.056) and quadratically (P = 0.067) as SID TrpLys increased, resulting in an optimum SID TrpLys 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 TrpLys of 15.78 and 15.64%, respectively. Based on the results from these 2 experiments, it seems that the optimum SID TrpLys is virtually unaffected by the dietary feedstuffs used as long as the diets are formulated on an SID AA basis.