Nutritive value of mixed proteins. 2. As determined by net protein utilization and protein efficiency ratio tests

1. A fish meal, meat meal, soya-bean meal, groundnut meal and sunflower-seed meal of known amino acid composition were evaluated individually, and combined in all possible pairs, by the estimation of net protein utilization (NPU) and protein efficiency ratio (body-weight gain: crude protein intake; PER) using rats. Each pair provided a total of 100 g protein/kg diet made up so that the amounts of the constituents were (w/w) 100:0, 80:20, 60:40, 20:80, and 0:100. 2. Marked synergistic effects were noted only for mixtures of sunflower-seed meal with soya-bean, fish and meat meals. 3. Chemical score ([amount of limiting amino acid/the rat's requirement for the same amino acid] X100; CS), but not essential amino acid index; geometric mean for the ratio, amount of essential amino acid: the rat's requirement for that amino acid, for all ten essential amino acids; EAAI), successfully predicted the rankings of all mixtures except groundnut meal-meat meal and groundnut meal-soya-bean meal, by both PER and NPU tests. 4. Although there is broad agreement linking results of PER and NPU tests with results obtained by a more practical feeding trial in which the mixtures were evaluated as supplements to cereals, neither of these two standard tests is capable of predicting in every instance the advantages to be gained by mixing protein concentrates.