Effect of the Composition and Autoclave Sterilization of Diets for Laboratory Animals on Pellet Hardness and Growth Performance of Mice

The aim of the study was to determine the effect of modifications of ingredient composition and autoclaving of feeds for laboratory animals on pellet hardness and growth performance of mice. Composition of two breeding diets, containing either casein or soybean meal as the main protein sources, was modified by a change of wheat to maize proportions, or by oil and/or fibre supplementation (in casein containing diets only). The diets were pelleted and autoclaved at 121°C for 20 min. Pellet hardness of nonautoclaved soya diets was smaller than of casein diets except for those supplemented with oil. Oil supplementation tended to reduce or reduced pellet hardness of nonautoclaved but not of autoclaved diets whereas change of cereal proportion and type of fibre had no effect. Autoclaving increased pellet hardness of all diets, cancelled softening effect of oil supplementation of nonautoclaved casein diets and reduced difference between casein and soya containing diets. Pellet hardness was correlated with fat, fibre, starch, ash and phosphorus content. In mice, total consumption of autoclaved diets was greater than of nonautoclaved diets. Body weight was not affected by diet whereas it was decreased by autoclaving only in the 3rd and 6th week of experiment, the differences being of a very small magnitude. Growth of male mice depended on nutrient content, especially fibre, ash, phosphorus and energy, whereas body weight of females was highly correlated with phosphorus content. The dependencies differed between weeks of experiment