Enhancing digestibility of corn fed to pigs at two stages of growth through management of particle size using a hammermill or a roller mill.

The experimental objective was to determine the role of mean particle size (PS), grinding method, and body weight (BW) category on nutrient, fiber, and energy digestibility of corn. A total of 48 barrows were housed in individual pens and randomly assigned to one of six dietary treatments for 11 d at two BW categories (55 kg and 110 kg). The six treatments consisted of corn ground at three different targeted mean PSs (300, 500, and 700 µm) using either a roller mill or a hammermill. Fecal samples were collected for the last 3 d of each feeding period. Titanium dioxide was used as an indigestible marker. Digestibility data were analyzed as a linear mixed model using the MIXED procedure of SAS. Finishing pigs had greater apparent total tract digestibility (ATTD) of dry matter (DM), gross energy (GE), and N than growing pigs (P = 0.02, P = 0.01, and P <0.01, respectively). The ATTD of DM, GE, and N was similar in pigs fed hammermilled corn across all PS treatments. However, in roller-milled corn, they increased as PS was reduced (P < 0.05). The ATTD of acid-hydrolyzed ether extract (AEE) in growing pigs was similar between corn ground at 700 and 500 µm, but it was increased by further reducing PS to 300 µm (P < 0.05). In finishing pigs, the ATTD of AEE increased as mean PS decreased from 700 to 300 µm (P < 0.05). The ATTD of AEE was similar in hammermilled corn at all three PS treatments. On the other hand, the ATTD of AEE was similar in corn ground in a roller mill to 700 and 500 µm, but it increased when PS was reduced to 300 µm (P < 0.05). In conclusion, reducing PS of corn with a roller mill increased digestibility of energy and nutrients, but there was less effect using a hammermill. It is possible that differences in SD, distribution, chemical composition, and the shape of the particles resulting from the two grinding processes help to explain the different response.