The availabilities of lysine, methionine and tryptophan in Pruteen by chick growth assay

The concentrations of available lysine, methionine and tryptophan in the single‐cell protein, Pruteena (ICI), have been determined by growth assay with young chicks. Symmetrical, six‐point, parallel‐line assays were used with weight gain and gain: food ratio as responses. All diets were balanced as far as possible, especially with respect to essential amino acid composition. Concurrently with the determination of each amino acid in Pruteen, its contents in typical fish and soya bean meals were determined. The assays were acceptable by the statistical criteria used. They yielded estimates of potencies that were realistic in relation to the total contents of lysine, methionine and tryptophan in Pruteen, fish and soya bean meals. The variances of potency estimates were typical of such assays. The values obtained for Pruteen considering both weight gain and gain:food ratio as responses, were about 40 g lysine, 18 g methionine and 8.7 g tryptophan kg−1 air‐dry matter. For lysine and methionine these represent high availabilities of total amino acids. The availability of tryptophan is less clear because of uncertainty about the total content of tryptophan in Pruteen.