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Technical Resources

New methodology to measure internal particle size in pellets and to quantify the degree of grinding during pelleting

Bonilla, S., J. Gulizia, S. Sasia, M. Rueda and W. Pacheco

Grinding is one of the highest cost centers during feed manufacturing and it is typically accomplished using hammermills or roller mills. In pelleted diets, the pelleting process leads to additional grinding, which can lead to inconclusive results regarding optimum particle size in broiler diets. The aim of this study was to develop a new methodology to evaluate average particle size of pellets after particle agglomeration and determine the degree of grinding that occurs during pelleting. Corn was ground using a two-pair roller mill to obtain 3 corn particle sizes (801, 1587 and 2394 μm). Ingredients were blended using a twin shaft mixer to produce the mash diets, which were steam conditioned at 77°C with a retention time of 45 seconds and pelleted through a 4.0 mm pellet die. A total of 36 mash and pellet samples were collected at even intervals from a 1-ton batch for each corn particle size. Twelve mash samples were analyzed as collected using the ASABE method S319.4 while 12 mash and 12 pellet samples went through an additional procedure of hydration and dehydration using a novel methodology to separate agglomerated particle after pelleting. The objective of hydration and dehydration of mash diets prior to pelleting was to ensure that the new methodology did not alter particle size or particle size distribution. The experiment consisted of a factorial arrangement of 3 corn particle sizes and 3 feed forms (meal, hydrated meal, and pellet). Data were statistically evaluated using the GLM procedure of JMP and means were separated by Tukey’s HSD with a statistical significance considered at P<0.05. In diets with corn particle size of 801 μm and 1587 μm, meal and hydrated meal had higher (P<0.05) particle size than the internal particle size within pellets (914 and 963 vs 716 μm) and (1311 and 1352 vs 779 μm) respectively. In diets with corn particle size of 2,394 μm, hydrated meal had higher (P<0.05) particle size compared to the particle size within pellets (1678 vs 1085 μm) with the meal having an intermediate particle size of 1590 μm.

This new methodology helped to quantify the degree of grinding that occurs during pelleting, which could help the poultry industry to accurately determine the optimum particle size requirements of broilers.