EFFECTS OF MILL TYPE AND PARTICLE-SIZE UNIFORMITY ON GROWTH-PERFORMANCE, NUTRIENT DIGESTIBILITY, AND STOMACH MORPHOLOGY IN FINISHING PIGS

The effects of particle size uniformity and mill type used to grind co rn were determined in three experiments. In Exp. 1, 120 pigs (47.8 kg initial BW) were used. Treatments were 1) a 40:60 blend of coarsely ro lled (in a roller mill) and finely ground (in a hammermill) corn with a large standard deviation (s(gw)) of particle size (s(gw) of 2.7), 2) hammermilled corn with an s(gw) of 2.3, and 3) roller-milled corn wit h of 2.0. Mean particle size of the corn was approximately 850 mu m fo r all treatments. Growth performance was not affected (P > .11); but, stomach keratinization tended to be less severe (P < .08) and apparent nutrient digestibilities were greater (P < .008) when the s(gw) was s maller. In Exp. 2, 128 pigs (55.3 kg initial BW) were used. Treatments were corn ground in a hammermill and a roller mill to 800 and 400 mu m. Pigs fed corn ground to 400 mu m were more efficient (P <.004) and had greater apparent digestibilities of DM, N, and GE (P < .001) than pigs fed corn ground to 800 mu m. Mill type did not affect growth perf ormance (P > .40), but pigs fed corn ground in the roller mill had gre ater apparent nutrient digestibilities (P < .008). In Exp. 3, 128 pigs (67.3 kg initial BW) were used. Treatments were corn ground to 400 mu m in a hammermill and a roller mill fed in meal and pelleted forms. P igs fed pelleted diets had greater ADG (P < .003) and gain/feed (P < . 03) but also had greater incidence of ulcers (P < .04). Pigs fed rolle r-milled corn were more efficient (P < .05) and had a lower incidence of ulcers (P < .04), but diets with hammermilled corn had lower s(gw) and greater apparent digestibilities of nutrients (P < .02). Our resul ts suggest that mill type had inconsistent effects on growth performan ce, but more uniform particle sizes consistently gave greater nutrient digestibilities.