2-Keto-4-(Methylthio)Butyric Acid (Keto Analog of Methionine) Is a Safe and Efficacious Precursor of l-Methionine in Chicks ,

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Abstract
Relative bioefficacy and toxicity of Met precursor compounds were investigated in young chicks. The effectiveness of dl-Met and 2-keto-4-(methylthio)butyric acid (Keto-Met) to serve as l-Met precursors was quantified using Met-deficient diets of differing composition. Efficacy was based on slope-ratio and standard-curve methodology. Using l-Met as a standard Met source added to a purified diet, dl-Met and Keto-Met were assigned relative bioefficacy values of 98.5 and 92.5%, respectively, based on weight gain. Relative bioefficacy values of 98.5 and 89.3% were assigned to dl-Met and Keto-Met, respectively, when chicks were fed a Met-deficient, corn-soybean meal-peanut meal diet. Thus, both dl-Met and Keto-Met are effective Met precursor compounds in chicks. Additionally, growth-depressing effects of l-Met, dl-Met, and Keto-Met were compared using a nutritionally adequate corn-soybean meal diet supplemented with 15 or 30 g/kg of each compound. Similar reductions in weight gain, food intake, and gain:food ratio were observed for each compound. Subjective spleen color scores, indicative of splenic hemosiderosis, increased linearly (P < 0.01) with increasing intakes of each compound, suggesting a similarity in overall toxicity among these compounds. Because conversion of Keto-Met to l-Met in vivo merely requires transamination, Keto-Met may prove to be a useful supplement not only in food animal production, but also as a component of enteral and parenteral formulas for humans suffering from renal insufficiency.

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