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Impact of particle size and grinding method (roller or hammermill) on apparent total tract digestibility of energy in growing pigs
The objective of this study was to determine the impact of mean particle size (PS) of corn and wheat with two different grinding technologies on the apparent total tract digestibility (ATTD) of GE in growing pigs (GP) and in finishing pigs (FP). Ninety six growing barrows (BW= 54.6 ± 0.4 kg) and ninety six finishing barrows (BW =110.2 ± 0.8; PIC 337 sires x C22 or C29), providing 8 observations per dietary treatment were housed in individual pens and randomly assigned to 1 of 12 treatments. Corn and wheat were ground to three different PS (300, 500, and 700 microns), using either a roller mill (RM) or a hammermill (HM). Fecal samples were collected for the last three days of an 11d feeding period. Titanium dioxide was used as an indigestible marker. Data were analyzed using the MIXED procedure of SAS. Particle size interacted with growth stage (P < 0.01); ATTD of GE increased in GP by lowering PS (81.4, 84.7 and 85.6% for 700, 500 and 300 microns respectively; P < 0.05); in FP, ATTD of GE increased from 700 to 500 microns (P < 0.05) and remained constant at 300 microns (83.65, 86.50 and 86.20% respectively). Particle size interacted with ingredient (P <0.01); ATTD of GE improved in pigs fed corn by lowering PS (81.55, 84.44 and 85.94% for 700, 500 and 300 microns respectively); in pigs fed wheat, ATTD of GE increased from 700 to 500 microns but was similar at 300 microns (83.49, 86.75 and 85.87% respectively). Particle size interacted with grinding technique (P < 0.01); ATTD of GE increased by lowering PS with RM (82.42, 85.40 and 86.68% for 700, 500 and 300 microns respectively; P < 0.05); for HM ATTD of GE increased (P < 0.05) from 700 to 500 microns but was similar (P > 0.05) at 300 microns (82.62, 85.79 and 85.14% respectively). In conclusion lowering PS improved ATTD of GE. This improvement was accentuated more in growing pigs than finishing pigs, in corn more than in wheat and when using the RM than the HM.
Keywords: roller mill, hammermill, particle size