The effect of adding water into the mixer on pelleting efficiency and pellet quality in diets for finishing pigs without and with use of an expander

Two diets for finishing pigs were used to determine the effect of adding water into the mixer on processing characteristics and pellet quality. Diet 1 was based on barley, oats and soybean meal (barley-based diet) and Diet 2 was based on maize and soybean meal (maize-based diet). Both diets were produced without and with use of an expander. Adding up to 120 g water/kg into the mixer prior to steam conditioning and pelleting (steam conditioning) of the barley-based diet, improved pelleting efficiency, pellet durability index (PDI) and modified PDI (with five hexagonal nuts added into the tumbling box), by 15, 10 and 10%, respectively. When water was added into the mixer prior to expanding the barley-based diet, PDI increased from 93 to 95% and modified PDI from 91 to 94%. The maize-based diet was processed with motor load held constant to maximize feed mill output, and production rate held constant to minimize energy use. At a constant motor load and a constant production rate, adding up to 30 g water/kg into the maize-based diet prior to steam conditioning increased pelleting efficiency by 22 and 9%, PDI was improved from 84 to 89% and from 79 to 87%, respectively. Expander conditioning of the maize-based diet increased PDI from 92% at none to 94% at 30 g/kg water addition. Correspondingly, modified PDI was increased from 89 to 93% at none and 30 g water/kg into the mixer prior to expander conditioning. The overall conclusion from the experiment was that adding water into the mixer before steam conditioning improved pelleting efficiency and pellet quality in barley- and maize-based diet for finishing pigs.