Uric acid excretion by the chick as an indicator of dietary protein quality.

The objective of this investigation was to determine whether uric acid excretion could serve as an indicator of dietary protein quality. In the first study, 15% protein diets were formulated using either whole egg protein, soybean meal, safflower meal or casein, or the latter 3 proteins supplemented with their most limiting amino acid (methionine, lysine and arginine, respectively). Chicks fed diets supplemented with the limiting amino acid grew more rapidly and efficiently and excreted less uric acid. Good agreement was noted between uric acid excretion and protein efficiency ratio (PER) as indicators of protein quality. Two studies were conducted with chicks fed diets containing raw soybean flakes or flakes autoclaved for varying periods of time and fed with or without methionine and lysine supplementation. Similar chick performance, uric acid excretion and PER were noted with chicks fed the soybean flakes which had been autoclaved for 20, 40 or 120 min. Poorer chick performance and PER were noted with chicks fed soybean flakes or flakes autoclaved for 10 min. When the diets were supplemented with methionine and lysine, the negative effects of inadequate heating were partially alleviated. The results indicated that adequate heating and amino acid supplementation of soybean flakes were both essential for maximal chick performance, that the two factors influence the utlization of the protein in different ways and that the two effects were additive.