Potential of Dimensional Measurements of Individual Pellets as another Measure for Evaluating Pellet Quality

Abstract

Pellet durability index (PDI) detailed in ASABE Standard S269.4 has been the widely accepted measure for pellet quality and, by extension, the measure for evaluating the effect of ingredients and pelleting process variables on the quality of pelleted animal and poultry feed products. PDI is calculated as the mass percentage of intact pellets remaining after tumbling a 500 g sample in a durability tester for 10 min. In the case where pellet quality is good, oftentimes the resulting PDI for different experimental treatments are very close to each other. In these situations, it is desirable to have another measurement that would allow for finer discrimination among treatments. It is hypothesized that linear dimensions of animal feed pellets would vary as a function of formulation and the pelleting process variables for a consistent knife setting in the pellet mill. In this regard, the average linear dimensions of pellets in a unit mass sample of a pelleted product could be used as another measure for pellet quality. This hypothesis was tested in a study involving effectiveness testing of different inclusion levels of a test pelleting aid in a typical corn-soy diet. Even with a minimized sample size choice, measuring dimensions of individual pellets is a tedious activity and so the study was extended to take advantage of machine vision for counting pellets in a unit sample and simultaneously measuring their dimensions. Since length measurements for the cold and hot pellets varied only by 1.02 and 2.03 mm, respectively, pellet length does not seem to be a good discriminator of pellet durability between pelleted products tested. With the wider range in numerical values of the PDIs obtained aggressively (23.0 to 81.0%), PDI from aggressive testing appears to be the better measurement for discriminating quality among pelleted products.