ARS | Publication request: Determining the Optimum Dietary Tryptophan to Lysine Ratio in Growing Pigs Fed Diets Formulated with Hhigher Levels of Other Essential Amino Acids

Submitted to: Journal of Animal Science
Publication Type: Abstract Only
Publication Acceptance Date: March 16, 2009
Publication Date: March 16, 2009
Citation: Quant, A.D., Lindemann, M.D., Cromwell, G.L., Kerr, B.J., Payne, R.L. 2009. Determining the Optimum Dietary Tryptophan to Lysine Ratio in Growing Pigs Fed Diets Formulated with Hhigher Levels of Other Essential Amino Acids. Journal of Animal Science. 87:84.

Technical Abstract: Studies on amino acid (AA) ratios require the first limiting AA (generally Lys) to be set below the requirement estimate. Graded levels of the AA being investigated are then fed to determine the required ratio. Essential AA (EAA) not under investigation are often set at their presumed requirement ratio relative to that first limiting AA. A 21-day study was conducted to evaluate the optimum standardized ileal digestible (SID) Trp:Lys ratio in 20 to 50 kg pigs fed diets where the EAA not being examined were formulated to 100% of a previously determined Lys requirement (resulting in a presumed greater excess of EAA). Crossbred pigs (n = 120; initial BW: 24.1 ± 2.7 kg) were blocked by BW and gender and allotted to 6 diets with 5 pigs/pen. Diets were formulated to a SID Lys of 0.66% (0.74% total Lys) with the addition of L-Trp to the basal diet to create 6 SID Trp:Lys ratios (13.08, 14.06, 15.04, 17.00, 18.95, and 20.91%). Treatments were designed to bracket the optimum SID Trp:Lys ratio of 15.7% (determined in our previous studies) with 3 diets above and below this ratio. Other EAA were set based on a Lys requirement of 0.905% total Lys. Pigs were allowed ad libitum access to feed and water throughout the study. As SID Trp:Lys ratios increased from 13.08% to 20.91%, ADG increased (0.429, 0.476, 0.561, 0.714, 0.766, and 0.792 kg/d) linearly (P < 0.001) and quadratically (P = 0.004), with linear broken–line analysis indicating an optimum SID Trp:Lys ratio of 17.93% (P < 0.001). Plasma urea N concentrations decreased (10.62, 9.51, 8.83, 7.93, 8.08, and 8.63 mg/dL) linearly (P = 0.011) and quadratically (P = 0.015) as SID Trp:Lys ratios increased, displaying an optimum SID Trp:Lys of 16.17% (P = 0.009). Based on the average of ADG and PUN optima, the optimum SID Trp:Lys ratio was determined to be 17.05%, which equates to 17.54% on a total AA basis. This ratio was marginally higher than that of previous studies at our station with lower EAA levels, suggesting that the optimum ratio may be impacted by the methodology used in these type of studies.