Impact of crude glycerol on feed milling characteristics of swine diets

This study evaluated the effect of crude glycerol on feed processing of nursery and finisher diets for pigs. In Exp. 1, complex nursery pig diets were mixed in a double ribbon mixer with glycerol levels of 0, 25, and 50 g/kg replacing maize on a weight basis and pelleted (74 °C conditioning temperature (CT) and 4.4 mm × 29 mm die size). In Exp. 2, finisher diets (maize–soybean meal based with 30 g/kg added fat) were mixed in a double ribbon mixer with glycerol included at 0, 25, and 50 g/kg replacing maize on a weight basis and pelleted (74 °C CT; 4.4 mm × 29 mm die size). A second control feed was pelleted at a standard CT of 85 °C. There were three replications per treatment for Exp. 1 and 2. In Exp. 1, flowability of mash nursery diets improved linearly (P<0.001) with glycerol. For pelleting, electrical consumption decreased linearly (P=0.02), production efficiency (P=0.01), pellet durability index (PDI, P=0.001) and modified PDI (included 3 hexagonal nuts, P<0.001) increased linearly, and hot pellet temperature after the pellet die decreased linearly (P<0.001) with increasing levels of glycerol. In Exp. 2, flowability of mash finisher diets improved linearly with increasing glycerol (P=0.03). For pelleting, increasing glycerol linearly increased pellet mill efficiency (P=0.005) and PDI (P<0.001), and decreased hot pellet temperature (P=0.05). Hot pellet temperature and PDI were greater (P<0.001) and pellet mill efficiency (P=0.06) tended to be greater for CT of 85 °C compared to 74 °C. In conclusion, glycerol supplementation improved flowability of meal and pelleting efficiency of nursery and finishing diets and required the use of a lower pelleting temperature while improving production efficiency and maintaining pellet quality.