Chung T K, Baker D H
Department of Animal Sciences, University of Illinois, Urbana 61801.
J Anim Sci. 1992 Apr;70(4):1182-7. doi: 10.2527/1992.7041182x.
Three pig experiments were conducted using a chemically defined, amino acid diet under conditions in which all nutrients were 100% bioavailable to assess the maximal portion of the sulfur amino acid (SAA) requirement that could be furnished by cystine (Cys). In Exp. 1, a methionine (Met)-deficient diet containing .12% L-Met and .40% L-Cys was supplemented with graded levels of L-Met. Pigs weighing 10 kg initially responded quadratically (P less than .05) to Met supplementation. A two-slope, broken-line regression model (weight gain regressed on percentage of dietary Met) estimated an infection point at .23% dietary Met. A constant level of .46% dietary SAA with differing Met:Cys weight (wt:wt) ratios was used in Exp. 2. Pigs fed Met:Cys ratios of 60:40 and 50:50 had similar (P greater than .05) weight gains, but pigs fed a 40:60 Met:Cys ratio gained less (P less than .05) than those fed the other diets. Maintaining dietary sulfur at .111% in Exp. 3, pigs fed Met:Cys ratios (wt:wt) of 100:0, 55:45, 50:50, and 45:55 gained weight at similar (P greater than .05) rates, but pigs fed the 45:55 Met:Cys ratio had a tendency to produce lower weight gains. Regardless of whether a constant dietary SAA or sulfur level was maintained, no more than 50% of the young pig's total SAA requirement (wt:wt) could be furnished by Cys.
进行了三项猪实验，实验采用化学定义的氨基酸日粮，在所有营养素生物利用率均为100%的条件下，评估胱氨酸（Cys）可提供的硫氨基酸（SAA）需求量的最大比例。在实验1中，向含0.12% L-蛋氨酸（Met）和0.40% L-胱氨酸的蛋氨酸缺乏日粮中添加不同水平的L-蛋氨酸。初始体重为10 kg的猪对蛋氨酸补充呈二次反应（P<0.05）。一个双斜率折线回归模型（体重增加量对日粮蛋氨酸百分比进行回归）估计日粮蛋氨酸的感染点为0.23%。实验2使用了日粮SAA水平恒定为0.46%、蛋氨酸与胱氨酸重量（wt:wt）比例不同的日粮。饲喂蛋氨酸与胱氨酸比例为60:40和50:50的猪体重增加相似（P>0.05），但饲喂蛋氨酸与胱氨酸比例为40:60的猪体重增加量低于其他日粮组（P<0.05）。在实验3中，日粮硫含量维持在0.111%，饲喂蛋氨酸与胱氨酸比例（wt:wt）为100:0、55:45、50:50和45:55的猪体重增加速率相似（P>0.05），但饲喂蛋氨酸与胱氨酸比例为45:55的猪体重增加有降低的趋势。无论日粮SAA水平或硫水平是否恒定，胱氨酸提供的量均不超过幼猪总SAA需求量（wt:wt）的50%。
