OPTIMUM PARTICLE-SIZE OF CORN AND HARD AND SOFT SORGHUM FOR NURSERY PIGS

A total of 240 weanling pigs (22 d of age and 5.3 kg average BW) were used to determine the effects of particle size of corn and two sorghum hybrids on diet processing, growth performance, apparent digestibilit y of nutrients, and morphology of the stomach and intestines in weanli ng pigs. Treatments were corn, hard endosperm sorghum, and soft endosp erm sorghum milled to particle sizes !geometric mean) of 900, 700, 500 , and 300 mu m, in a 3 x 4 factorial arrangement. All diets were pelle ted and the pigs were allowed to consume feed and water on an ad libit um basis. As particle size was reduced, production rate (tons/hour) de creased and energy required to mill (kilowatt hours/ton) increased. Co rn required more energy to mill and had a lower production rate than t he sorghums. For d 0 to 14, ADG and gain/feed increased linearly (P < .009 and P < .002, respectively) as particle size was decreased to 300 mu m. However, there was a grain source x particle size interaction; pigs fed corn responded to particle size reduction more than pigs fed the sorghums (P < .04). For d 0 to 35, pigs fed diets with corn grew 2 3% faster and were 6% more efficient (P < .001) than pigs fed diets wi th sorghum. Gain/feed responded quadratically to reduction of particle size (P < .01), with maximum gain/feed at 500 mu m for all grains. Lo west cost of gain (including milling and ingredient -costs) was achiev ed at 500 to 700 mu m for corn and 500 mu m for the hard and soft sorg hums. These data suggest that response to reducing particle size is gr eatest during the first 2 wk postweaning and that optimal particle siz e for corn and sorghums increases with age of nursery pigs.