Potential of dimensional measurements of individual pellets for evaluating feed pellet quality

Authors: Pordesimo, Lester; IGATHINATHANE, CANNAYEN - North Dakota State University; BEVANS, BASIL - Adm Animal Nutrition; HOLZGRAEFE, DAVID - Adm Animal Nutrition

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/2022
Publication Date: 10/4/2023
Citation: Pordesimo, L.O., Igathinathane, C., Bevans, B.D., Holzgraefe, D.P. 2023. Potential of dimensional measurements of individual pellets for evaluating feed pellet quality. Applied Engineering in Agriculture. 38(5):777-785. https://doi.org/10.13031/aea.14845.
DOI: https://doi.org/10.13031/aea.14845

Interpretive Summary: Pellets for animal feed are produced by applying moisture, heat, and mechanical pressure to ground nutritional ingredients and they promote better feed efficiency and handling. High quality pellets should withstand repeated handling during transportation and storage without excessive breakage or generation of fine particles. The Pellet Durability Index (PDI) is a widely accepted measure for pellet quality in the U.S. that is calculated as the percentage of intact pellets remaining after tumbling for 10 min. In some cases there is a need for finer discrimination among different levels of pellet quality. Using machine vision to rapidly and accurately measure dimensions of pellets could be an alternative measure of pellet quality that provides greater resolution in evaluating different pelleting processes. This hypothesis was tested in a study evaluating different 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 matched to measurements taken manually and varied with pelleting methods evaluated. However, these linear dimension measurements were not a good discriminator of pellet quality between pelleted products because of the narrow range in measurement numbers. Determining PDI of pellets following an aggressive durability test using a tumbling can with steel hexagonal screw nuts added with the pellets was found to be a better discriminator of quality among pelleted products. This finding about feed pellet quality evaluation will enable animal feed manufacturers to develop better quality pelleted feeds through better selection of ingredients and processing variables that they can manipulate in their operations.

Technical Abstract: Pellet durability index (PDI) detailed in ASABE Standard S269.4 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. This difficulty can be overcome by employing machine vision for the linear measurements, which may be implemented in an instrument and even be automated. 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 mm 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 hexagonal nuts), PDI from aggressive testing is the better discriminator of quality among pelleted products because of its greater resolution.