Corn kernel hardness and drying temperature affect particle size post-hammer-milling and pellet quality in broiler and swine diets

The particle size (PS) of ground corn affects the live performance, nutrient digestibility, energy utilization, and gut health of poultry and swine. Endosperm hardness influences kernel breakability. The interactive effects of corn moisture content at harvest and drying temperature (DT) can also affect starch-protein matrix structure, breakage susceptibility, and pellet durability. The objective of this study was to evaluate the effects of drying temperature (35 or 120 °C) in two yellow-dent corn hybrids with different kernel hardness (average and hard) on the geometric mean diameter (dgw) and standard deviation by weight (Sgw) when hammermilled, and pellet quality. Four different settings combinations of tip speeds (4213, 3862, 3335, and 2458 m/min) and screen of 8/64", 3.18 mm (8 −8); 20/64", 7.94 mm (20 −20); 24/64", 9.53 mm (24 −24); and 24/64", 9.53 mm (24 −24) respectively were used to target four dgw (400, 700, 925, and 1250 µm). After grinding, the 400 and 700 µm corn were included in broiler and sow diets to assess the impact of these treatments on the pellet durability index (PDI). Grinding and pelleting data were analyzed using a 2 × 2 factorial arrangement of two corn varieties (CV) and two DT in a randomized complete block design with blocks by grinding or pelleting event. The average hardness CV generally had the lowest dgw. The hard CV had the biggest dgw when kernels were dried at 35 °C, and the tip speed setting was 3335 m/min. Drying at 120 °C increased dgw for the average hardness CV when the target PS were 700, 925, and 1250 µm, but caused no increase in dgw at the lowest target PS. In contrast, the dgw of hard CV was not affected by DT when ground to target 700 and 1250 µm and increased at 400 µm with the high DT. The average hardness CV had higher Sgw, especially when dried at 35 °C. Higher particle uniformity (lower Sgw) was observed with hard CV. Diets containing the hard CV presented better PDI than diets with the average CV. Better broiler feed PDI was observed with corn dried at 120 °C than at 35 °C. However, this effect was the opposite when grinding at a lower PS target for sow gestation diets. The PS distribution and damaged starch of corn affected PDI. Higher corn DT affected dgw and Sgw differently depending on CV and improved PDI in broiler diets, while 35 °C DT improved PDI in sow diets.