Abstract
The objective was to determine the interactive effects of reducing particle size of corn and pelleting on the apparent total tract digestibility (ATTD) of gross energy (GE), fiber, fat, calcium, and phosphorus, N balance, and net energy (NE) in corn-soybean meal diets fed to pigs. Six corn-soybean meal-based diets were arranged in a 3 × 2 factorial with 3 particle sizes of corn (i.e., 700, 500, or 300 μm) and 2 diet forms (i.e., meal or pelleted). Pigs were allowed ad libitum access to feed and water. Pigs (n = 24; initial body weight = 29.52 kg; SD = 1.40) were housed in indirect calorimetry chambers and allotted to the 6 diets using a 6 × 6 Latin square design with 6 chambers (i.e., 4 pigs/chamber) and six 15-day periods. Fecal and urine samples were quantitatively collected during a 6-day period following 7 days of adaptation and O(2) consumption and CO(2) and CH(4) productions were measured during fed and fasting states. The statistical model included diet as fixed effect and chamber and period as random effects. Contrast coefficients were used to determine effects of diet form, linear effects of particle size, and the interaction. Results indicated that reducing the particle size of corn increased the ATTD of GE and of acid hydrolyzed ether extract (AEE) in meal diets, but not in pelleted diets (interaction, P < 0.001; Table 1). The ATTD of Ca was reduced in diets containing 500 μm corn by pelleting to a greater extent than in diets containing 300 or 700 μm corn by pelleting (interaction, P = 0.004), but regardless of corn particle size, the ATTD of P was less (P = 0.037) in pelleted diets compared with meal diets. The ATTD of N increased to a greater extent in meal diets than in pelleted diets as particle size was reduced (interaction, P = 0.021). The NE of diets increased as particle size of corn was reduced from 500 to 300 μm in meal diets and from 700 to 500 μm in pelleted diets (interaction, P = 0.004). The ATTD of GE, N, and AEE, and the NE of diet were greater (P < 0.05) in pelleted than in meal diets, but the ATTD of Ca and P was greater (P < 0.05) in meal diets than in pelleted diets. The ATTD of total dietary fiber and N retention were not affected by diet form or particle size of corn. In conclusion, reducing the particle size of corn from 700 to 300 μm increases the NE of a corn-soybean meal diet due to increased ATTD of GE, N, and AEE, but the increment in NE or the ATTD of nutrients depends on diet forms.