Evaluation of optimum lysine and threonine supplements to a wheat and barley-based diet in rats

Experiments were conducted on growing male SPF-rats to study the optimum supplementation with essential amino acids of diets containing wheat and barley (1.4:1) as the only source of nitrogen. In growth and balance experiments comprising 30 and 17 combinations of L-lysine and L-threonine, respectively, the concentrations of the two amino acids corresponding to maximum body weight gain, feed conversion efficiency, biological value of protein and net protein utilization were calculated using multiple regression analysis. Addition of lysine and threonine to the basal diet markedly improved the nutritional value of cereal proteins. The optimum concentrations found were 0.69–0.70% total dietary lysine and 0.52–0.55% total dietary threonine. Statistical analysis showed that the number of observations used for the estimation of regression functions in the growth experiment could be reduced to ca. 100 without substantially affecting precision.