title: 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) Trp:Lys 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 Trp:Lys determined using broken-line analysis. Experiment 1 evaluated the optimum SID Trp:Lys 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 Trp:Lys 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 Trp:Lys 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 Trp:Lys (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 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 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 of 15.83% (P = 0.007). Experiment 2 evaluated the optimum SID Trp:Lys 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 Trp:Lys (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 increased in Exp. 2, ADG increased linearly (P = 0.007) with the optimum SID Trp:Lys of 15.99% (P = 0.048). Plasma urea N concentrations decreased linearly (P = 0.056) and quadratically (P = 0.067) as SID Trp:Lys increased, resulting in an optimum SID Trp:Lys 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 of 15.78 and 15.64%, respectively. Based on the results from these 2 experiments, it seems that the optimum SID Trp:Lys is virtually unaffected by the dietary feedstuffs used as long as the diets are formulated on an SID AA basis.
authors.affiliation: Department of Animal and Food Sciences, University of Kentucky, Lexington 40546, USA.
authors.forename: A D
authors.initials: AD
authors.lastname: Quant
authors.forename: M D
authors.initials: MD
authors.lastname: Lindemann
authors.forename: B J
authors.initials: BJ
authors.lastname: Kerr
authors.forename: R L
authors.initials: RL
authors.lastname: Payne
authors.forename: G L
authors.initials: GL
authors.lastname: Cromwell
mesh_terms: D000824:Animal Nutritional Physiological Phenomena / Q000502:physiology; D000818:Animals; D004032:Diet / Q000662:veterinary*; D019587:Dietary Supplements; D004063:Digestion / Q000502:physiology; D005260:Female; D001467:Hordeum / Q000737:chemistry / Q000378:metabolism; D007082:Ileum / Q000502:physiology*; D008239:Lysine / Q000032:analysis / Q000378:metabolism*; D008297:Male; D013552:Swine / Q000254:growth & development / Q000502:physiology*; D014908:Triticum / Q000737:chemistry / Q000378:metabolism; D014364:Tryptophan / Q000032:analysis / Q000378:metabolism*; D003313:Zea mays / Q000737:chemistry / Q000378:metabolism*
chemical_list: D014364:Tryptophan; D008239:Lysine