A STANDARD PROCEDURE FOR MEASURING PELLET HARDNESS OF RODENT DIETS

A Chatillon Model TCM-200 test stand with exchangeable flat horizontal or concave receptacle bases and a DFI-200 gauge load cell with multip le types of upper exchangeable test jaws (large round-flat, medium rou nd-flat, chisel, bullet, and cone-shaped) were compared by using preau toclaved and autoclaved NIH-31 rodent diet pellets to determine which type of hardness testing system would give the most accurate and repro ducible results for measuring pellet hardness. The type and size of th e contact area of the upper jaws significantly affected the force requ ired to break the pellets. Significant differences were observed betwe en the flat-horizontal and concave receptacle bases in the force requi red to break the pellets when using the two round-flat upper jaws. In contrast, similar results were obtained with both bases when the bulle t, chisel, or cone-shaped upper jaws were used. Autoclaved pellets wer e 69.4% (range, 49 to 94%) harder than preautoclaved pellets. These re sults suggest that different testing systems can be used for measuring pellet hardness and that a standard procedure must be used in order t o compare pellet hardness results between different testing laboratori es. It was concluded that the flat-horizontal base and the larger roun d-flat end upper jaw gave the most reproducible results for measuring pellet hardness.