Abstract
The objective of this experiment was to determine the effect of conditioning temperature on pellet durability index (PDI) and pellet hardness. A nursery pig diet was formulated to contain 25% spray-dried whey. Treatments consisted of three different conditioning temperatures: 54, 63, and 71°C. Diets were steam conditioned (245 mm × 1397 mm Wenger twin staff pre-conditioner, Model 150) for approximately 30 sec and pelleted using a 1-ton 30-horsepower pellet mill (1012-2 HD Master Model, California Pellet Mill) with a 4.8 mm × 31.8 mm pellet die (L:D 6.7). The production rate was set at 900 kg/h. Treatments were pelleted at 3 separate time points to provide 3 replicates per treatment. Samples were collected directly after discharging from the pellet mill and cooled in an experimental counterflow cooler. Samples were analyzed for PDI using the Holmen NHP 100 for 60 sec (TekPro Ltd, Norfolk, UK). Pellet hardness was determined by evaluating the peak amount of force applied before the first signs of fracture. Although conditioning temperature was increased in a linear fashion, a quadratic increase (P < 0.002) in hot pellet temperature (HPT) was observed. The HPT were 68, 72, and 74°C for diets conditioned to 54, 63 and 71°C, respectively. Increasing conditioning temperature resulted in increased (linear, P < 0.045) PDI and pellet hardness. As conditioning temperature increased from 54, to 71°C PDI increased from 87% to 92% and the force required to crush pellets increased from 13.5 to 15.9 kg. There was a tendency for a correlation (P < 0.076, r = 0.618, r2 = 0.382) between pellet hardness and PDI. Overall, increasing the conditioning temperature increased pellet hardness and pellet durability.
The Effect of Pellet Mill Production Rate and Knife Distance on Pellet Quality
