POTENTIAL OF DIMENSIONAL MEASUREMENTS OF INDIVIDUAL PELLETS FOR EVALUATING FEED PELLET QUALITY

Pellet durability index (PDI) detailed in ASAE Standard S269.4 (ASAE Standards, 2007) has been the widely accepted measure for pellet quality in the U.S. and, by extension, the measure for evaluating the effect of ingredients and pelleting process variables on the quality of pelleted feed products. The PDI is calculated as the mass percentage of intact pellets remaining after tumbling a 500 g sample in a tumbling can durability tester for 10 min. In the case where pellet quality is good, oftentimes the resulting PDI for different experimental treatments are very close in magnitude. In these situations, it is desirable to have another measurement that would allow for finer discrimination among treatments. It was hypothesized that the average linear dimensions of animal feed pellets in a unit mass sample would vary as a function of formulation and pelleting process variables for a consistent knife setting in the pellet mill. This hypothesis was tested in a study involving effectiveness testing of varying inclusion levels of a potential pellet binder in a typical corn-soy swine diet pelleted by both conventional and cold pelleting processes. Pellet lengths and diameters measured by a machine vision implemented in ImageJ matched to measurements taken manually and varied with treatments. Pellet length varied with treatments but could not be a good discriminator of pellet durability between pelleted products because of the narrow range in measurement numbers (8.53 to 11.15 mm by machine vision). With the wider range in numerical values of the PDIs obtained through aggressive durability testing (23.0% to 81.0% in a tumble can with steel hexagonal screw nuts versus 91.0% to 97.5% in a tumble can without hexagonal nuts), PDI from aggressive testing is the better discriminator of quality among pelleted products because of its greater resolution.

Automated summary

Pellet durability index (PDI) is a widely accepted measure for pellet quality, but in some cases, a better discriminator is needed. The hypothesis that the average linear dimensions of animal feed pellets would vary based on formulation and pelleting process variables was tested. It was found that PDI obtained through aggressive durability testing is a better discriminator of quality among pelleted products due to its greater resolution compared to pellet length.