The impact of laboratory chow for rats in the experiments: Chemical and biological evaluation of nine grain-based diet options

Cereal-based diets formulated as semi-purified diets can provide flexibility for researchers, enabling open controlled formulas, besides being cheaper than purified diets. Seeking to widen the researchers’ options in their experimental design developments, we aimed at assaying the chemical score, growth performance and protein utilization of nine semi-purified experimental chows. These diets were formulated at 17.8%, 12% and 8% protein contents, using three variations of ingredients for each one, as follows: casein (C), casein+soybean meal (C+S, 1:1 w/w protein) and casein+soybean meal+corn gluten meal (C+S+G, 1:1:1 w/w protein), without cysteine supplementation and setting casein 17.8% (AIN-93G) as reference diet. The diets C and C+S (17.8%) had the Cys as the limiting amino acid once the addition of gluten turns the Lys as second limiting. All diets had the potential for promoting growth with body mass gain, feed conversion ratio (FCR; chow consumed per body weight gain, average 3.12) and feed efficiency ratio (FER; body weight gain per chow consumed, average 0.3), except for C+S+G 8% (FCR = 6 g; FER = 0.13). These variations were mainly due to the protein amounts independently from the protein ingredient used and could characterize the C+S+G 8% as unable to support growth. For the other parameters (digestibility, net protein ratio, net protein utilization and protein efficiency ratio), there were no relevant differences between the diets. We can conclude that 17.8%, 12% and 8% chows (C and C+S) allowed a proper combination of ingredients from the point of view of palatability, nutrient availability/utilization, metabolic processes, growth performance and feed utilization parameters.