Bioavailability of tryptophan in soybean meal and tryptophan retention in the carcasses of four-week-old ducks.
The objectives of the experiment were to determine the bioavailability of tryptophan in soybean meal for 4-wk-old ducks using the slope-ratio bioassay with L-tryptophan as the reference diet and estimate the efficiency of dietary tryptophan retention in the carcasses of 4- to 7-wk-old ducks. An initial representative group of 12 ducks with an average body weight of 1,951 g (SD = 69) were killed for carcass compositional analysis. A basal diet formulated to contain 1.13 g of tryptophan/kg and adequate in all other amino acids, was supplemented with 0.2, 0.4, or 0.6 g tryptophan/kg from L-tryptophan, or 0.2 or 0.4 g tryptophan/kg from soybean meal. Four pens of three 4-wk-old ducks received each of the six diets for 21 d. Ducks fed the basal diet and the basal diet supplemented with 0.2 or 0.4 g of L-tryptophan/kg for 21 d were used as the final slaughter groups for carcass compositional analysis. Dietary supplemental tryptophan from either L-tryptophan or soybean meal linearly increased final weight (P < 0.05), weight gain (P < 0.10), and gain:feed ratio (P < 0.05). Common-intercept, multiple linear regressions in slope-ratio methodology performed using weight gain and gain:feed ratio as dependent variables and grams of supplemental tryptophan/kg of diet as the independent variable gave 94 and 92% tryptophan bioavailability in soybean meal relative to L-tryptophan, respectively. Linear regression of tryptophan deposition in the carcass on tryptophan intake resulted in a 21% efficiency of carcass tryptophan retention above maintenance.
Adeola
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Department of Animal Sciences, Purdue University, West Lafayette, Indiana 47907, USA. ladeola@www.ansc.purdue.edu
D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001682:Biological Availability; D004372:Ducks / Q000378:metabolism*; D013025:Glycine max; D014364:Tryptophan / Q000008:administration & dosage / Q000378:metabolism* / Q000493:pharmacokinetics*; D015430:Weight Gain; D003313:Zea mays
D014364:Tryptophan