Sulfur amino acid nutrition of the growing puppy: Determination of dietary requirements for methionine and cystine

Abstract

English Pointer puppies were fed a crystalline amino acid diet (4002 kcal ME/kg) in a series of six experiments to determine the total sulfur amino acid (SAA) requirement and optimal cystinemethionine ratio for maximal rate and efficiency of weight gain. In experiments 1 and 2, equal-weight portions of cystine and methionine were fed at levels ranging from 0.25 to 0.65% of the diet. Rate of gain and feed conversion efficiency were maximized when SAA comprised 0.45% of the diet (112.4 mg SAA/100 kcal ME). The portion of the SAA requirement contributable by cystine was determined in experiments 3 and 4 to be 50% on a weight basis (55% on a molar basis). When a basal diet containing 0.1125% methionine (50% of the methionine requirement) and 0.1125% cystine was supplemented with an additional 0.225% cystine (cystine comprising 75% of SAA on a weight basis), reduced growth and skin lesions on the front paw and pad developed. A pair-feeding study established that the adverse effects of excess cystine were characteristic of an amino acid imbalance rather than an antagonism. Thus, excess cystine superimposed on a methionine deficiency reduced voluntary food (and methionine) intake which in large measure explained the growth depression and paw dermatitis.