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本試驗通過指示劑氨基酸氧化法研究了3個不同品種成犬的色氨酸需要量。試驗選用4頭切除卵巢或去勢的微型臘腸犬（5.28±0.29kg體重）、4頭切除卵巢的比格（9.32±0.41kg體重）、5頭去勢的拉布拉多獵犬（30.51±2.09kg體重）。試驗開始前飼喂14天的色氨酸充足基礎日糧（色氨酸含量0.482%，干基）。隨后所有犬飼喂色氨酸中度缺乏日糧2天（色氨酸含量0.092%，干基），然后將犬隨機分至7種日糧處理，日糧色氨酸水平分別為0.092、0.126、0.148、0.182、0.216、0.249、0.283%（干基），所有犬經過所有色氨酸水平處理。試驗日糧飼喂兩天后，犬經過獨立的指示劑氨基酸氧化試驗。總飼料量分成相同的13份；在第6餐，日糧中額外添加L-[1-13C]-苯丙氨酸（9.40mg/kg體重），隨后的每頓日糧中添加L-[1-13C]-苯丙氨酸（2.4mg/kg體重）。通過呼吸樣品中的豐度測量同位素穩態下13-CO2的總產量，通過間接側熱法檢測CO2總產量。通過兩相線性回歸模型測定色氨酸的維持需要量和95%置信區間。

Tryptophan (Trp) is an indispensable amino acid(AA) for dogs of all life stages; however, although Trp requirements for growing dogs are derived from 3 dose–response studies, there are no empiricaldata on Trp requirements for adult dogs at maintenance. The study objective was to determine Trp requirements of adult dogs of 3 different breeds using the indicator amino acid oxidation (IAAO) technique. Four spayed or neutered Miniature Dachshunds (5.28 ± 0.29 kg BW), 4 spayed Beagles (9.32 ± 0.41 kg BW), and 5 neutered Labrador Retrievers (30.51 ± 2.09 kg BW) were used. After a 14-dadaptation to a Trp-adequate basal diet (Trp = 0.482% dry matter), all dogs were fed a mildly Trp-deficient diet for 2 d (Trp = 0.092% dry matter) before being randomly allocated to receiving 1 of 7 concentrations of Trp supplementation (final Trp content in experimental diets was 0.092, 0.126,0.148, 0.182, 0.216, 0.249, and 0.283% dry matter) and all dogs received all Trp treatments. After 2-d adaptation to the experimental diets, dogs underwent individual IAAO studies. Total feed was divided in 13 equal meals; at the sixth meal, dogs were fed a bolus of L-[1-13C]-Phenylalanine (Phe) (9.40 mg/kg BW), and thereafter, L-[1-13C]-Phe was supplied (2.4 mg/kg BW) with every meal. Total production of 13CO2 during isotopic steady state was determined by enrichment of 13CO2 in breath samples and total production of CO2 measured using indirect calorimetry. The maintenance requirement for Trp and the 95% confidence interval (CI) were determined using a 2-phase linear regression model. Mean Trp requirements were estimated at 0.154, 0.218, and 0.157%(dry-matter) for Dachshunds, Beagles, and Labradors, respectively. The upper 95% CI were 0.187, 0.269, and 0.204% (dry-matter) for Dachshunds, Beagles, and Labradors. In conclusion, estimated Trp requirements are higher for Beagles compared with Labradors or Dachshunds, and all estimated requirements are higher than those currently recommended by the NRC and AAFCO.

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