Influence of Rat Strain and Protein Level on Protein Efficiency Ratio (PER) Determination

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Abstract
The influence of two main variables, rat strain and protein level, in protein efficiency ratio (PER) determination using male weanling rats was studied. Strain-to-strain variation in PER (grams of weight gain per gram protein consumed) was very marked, with values ranging from 2.20 to 3.24 obtained for ANRC casein as calculated after 4 weeks' growth. The procedure of correcting PER's obtained with test proteins relative to that obtained with ANRC casein was found to greatly reduce strain-to-strain variability in PER determination. The PER's obtained with ANRC casein, rolled oats, and wheat gluten supplemented with 3.4% of LMH and 1.0% of L-threonine were found to be relatively insensitive to changes in protein level in the range 9 to 16% dry weight. On the other hand, the PER obtained with wheat gluten supplemented with lysine alone was strongly dependent on protein level increasing from 1.4 at 9% of protein to 2.2 at 15% of protein (dry weight). This latter result was found to result from a threonine limitation which becomes less severe at higher protein levels.