The slope-ratio assay for rat was used to determine whether tryptophan (Trp) availability in soybean meal (SBM) is affected by the presence of other amino acids (AAs). In a preliminary study, rats were fed graded levels of Trp-supplemented diets to establish the Trp concentration range over which the weight gain response was linear. This range was found to be from 0.04% to 0.12% Trp. Subsequently, rats were fed basal (0.045% Trp) or Trp-supplemented diets from three different sources: l-Trp alone, SBM, or l-Trp mixed with other AAs to reflect AA levels in the test SBM (AA-mix). Weight gain in rats increased linearly with supplemental Trp intake (p < .05) for all Trp sources. Compared to the slope achieved with l-Trp alone, the estimated availability of Trp in SBM was 84.4%, while for the AA-mix it was 93.4%. It is evident that the 6.6% reduction in l-Trp availability in AA-mix is due to metabolic costs derived from excess levels of other AAs beside Trp, given that the absorption of crystalline l-Trp in the small intestine is 100%. In conclusion, the Trp availability of SBM was estimated to be around 90.4% (i.e., 84.4/93.4 × 100) after correcting for the effects of the other AAs in SBM.

中文翻译：

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斜率比生长测定技术在估算年轻大鼠豆粕中色氨酸利用率方面的应用。

使用大鼠的斜率比测定法确定豆粕（SBM）中色氨酸（Trp）的利用率是否受其他氨基酸（AAs）的存在影响。在一项初步研究中，给大鼠喂食了补充Trp饮食的分级水平，以建立体重增加反应呈线性的Trp浓度范围。发现该范围为0.04％至0.12％的Trp。随后，给大鼠喂食来自三种不同来源的基础饲料（0.045％Trp）或补充Trp的饮食：单独使用l-Trp，SBM或将l-Trp与其他AA混合以反映测试SBM（AA-mix）中的AA水平。对于所有Trp来源，大鼠的体重增加均与补充Trp摄入量呈线性增加（p <.05）。与仅使用l-Trp实现的斜率相比，SBM中Trp的估计利用率为84.4％，而AA混合物的Trp利用率为93.4％。显然，6。考虑到小肠中结晶性I-Trp的吸收为100％，AA混合物中的I-Trp利用率降低了6％，这是由于代谢成本是由Trp以外的其他AA过量引起的。总之，在校正了SBM中其他AA的影响后，SBM的Trp可用性估计约为90.4％（即84.4 / 93.4×100）。