Relative utilization of serine and glycine by chicks

Studies were conducted on the relative utilizaiton of glycine and serine by chicks fed basal crystalline amino acid diets devoid of these amino acids. The crystalline amino acid mixture was fed at one and three times the requirement levels, thereby stimulating uric acid synthesis at differing rates. In addition, 5 per cent L-glutamine replaced L-glutamic acid on an isonitrogenous basis in three diets containing normal levels of amino acids in the second study. Chicks fed diets devoid of glycine and serine grew less rapidly and less efficiently than chicks fed diets containing either serine or glycine plus serine. These decreases were roughly the same whether the diet contained normal or high levels of amino acids. Serine was as efficient as glycine in supporting chick growth and feed efficiency regardless of whether diets containing normal or high levels of amino acids were fed. Chicks fed diets containing high levels of amino acids grew approximately 81 per cent as rapidly, but 24 per cent more efficiently, than chicks fed normal levels of amino acids, and excreted approximately twice the amount of uric acid per gram of nitrogen consumed. In spite of increased uric acid excretion by chicks fed the high amino acid diets, the dietary void in glycine and serine was no more detrimental to chick growth or feed efficiency than that noted when normal levels of amino acids were fed. Feeding 5 per cent L-glutamine rather than L-glutamic acid in the diet containing normal levels of amino acids had little effect on weight gain, feed efficiency or uric acid excretion. The absence of cystine from the amino acid mixture used in the third study did not have a marked influence on the relative utilization of glycine and serine by the chick.