Effects of mill type 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 corn 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 rolled (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 with an s(gw) of 2.0. Mean particle size of the corn was approximately 850 micrometers for 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 smaller. In Exp. 2,128 pigs (56.3 kg initial BW) were used. Treatments were corn ground in a hammermill and a roller mill to 800 and 400 micrometers. Pigs fed corn ground to 400 micrometers were more efficient (P < .004) and had greater apparent digestibilities of DM, N, and GE (P < .001) than pigs fed corn ground to 800 micrometers. Mill type did not affect growth performance (P > .40), but pigs fed corn ground in the roller mill had greater apparent nutrient digestibilities (P < .008). In Exp. 3, 128 pigs (67.3 kg initial BW) were used. Treatments were corn ground to 400 micrometers in a hammermill and a roller mill fed in meal and pelleted forms. Pigs fed pelleted diets had greater ADG (P < .003) and gain/feed (P < .03) but also had greater incidence of ulcers (P < .04). Pigs fed roller-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 results suggest that mill type had inconsistent effects on growth performance, but more uniform particle sizes consistently gave greater nutrient digestibilities.