Effects of Corn Particle Size and Diet Form on Finishing Pig Growth Performance and Carcass Characteristics

A total of 960 pigs (PIC TR4 × Fast Genetics York-AND × PIC Line 02, initially 75.7 lb BW) were used in a 101-d trial to determine the effect of corn particle size and diet form on finishing pig growth performance and carcass characteristics. Pens were randomly allotted to 1 of 6 experimental treatments by initial BW with 8 pens per treatment and 20 pigs per pen. All diets were fed in four phases with the same cornsoybean meal–based diet containing 30% dried distillers grains with solubles (DDGS; Phases 1 to 3) or 15% DDGS (Phase 4) used for all diets. The 6 experimental treatments were arranged in a 2 × 3 factorial with main effects of final feed form (meal vs. pellet) and corn particle size (650 μ, 350 μ, or an equal blend of the 650 μ and 350 μ ground corn). Overall (d 0 to 101), linear particle size × diet form interactions were observed (P < 0.02) for ADFI and F/G due to ADFI decreasing and F/G improving as particle size was reduced for pigs fed meal diets but not for pigs fed pelleted diets. Pigs fed pelleted diets had increased (P < 0.001) ADG and final BW and improved (P < 0.001) F/G. As corn particle size decreased, ADG and ADFI decreased (P < 0.02) linearly. Pigs fed pelleted diets had increased (P < 0.001) HCW compared with pigs fed meal diets. Yield, backfat, and loin depth were not influenced by particle size or diet form.


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Effects of Corn Particle Size and Diet Form on Finishing Pig Growth Performance and Carcass Characteristics 1,2  Introduction Previous research at Kansas State University has shown that growth performance can be improved if corn particle size is reduced or if the diets are fed in pellet form, but grinding the complete diets was not beneficial (De Jong et al., 2012 4 ).In this previous trial, the entire corn fraction of each experimental diet was ground to a specific particle size using either a roller mill (650 µ) or a hammer mill (320 µ).By feeding a blend of corn SWINE DAY 2013 varying in particle size, the throughput of some feed mills could be increased, but little research has been conducted to determine the impact on finishing pig growth performance.Therefore, the objective of the current experiment was to determine the effect of corn particle size (650 µ, 350 µ, or an equal blend of the 650 µ and 350 µ ground corn) and diet form (meal vs. pellet) on finishing pig growth performance and carcass characteristics.

Procedures
The Kansas State University Institutional Animal Care and Use Committee approved the protocol used in this experiment.The study was conducted at the New Fashion Pork Research Facility (Round Lake, MN) in a commercial research-finishing barn located in northwestern Iowa.The double-curtain-sided barn was tunnel-ventilated with completely slatted flooring and deep pits for manure storage.Each pen was equipped with a 5-hole stainless steel dry self-feeder and a cup waterer for ad libitum access to feed and water.Daily feed additions to each pen were accomplished through a robotic feeding system (FeedPro; Feedlogic Corp., Willmar, MN) capable of providing and measuring feed deliveries for individual pens.
A total of 960 pigs (PIC TR4 × Fast Genetics York-AND × PIC Line 02, initially 75.7 lb BW) were used in a 101-d trial.Pens were randomly allotted by initial BW to 1 of 6 experimental treatments with 8 pens per treatment with 20 pigs per pen.Diets were fed in 4 phases, with Phases 1 through 4 fed from d 0 to 26, 26 to 46, 46 to 73, and 73 to 101, respectively (Table 1).Within each phase, the same corn-soybean mealbased diet containing 30% DDGS (Phases 1 through 3) or 15% DDGS (Phase 4) was used for all 6 experimental treatments.The 6 experimental treatments were arranged in a 2 × 3 factorial with main effects of final feed form (meal vs. pellet) and corn particle size (650 µ, 350 µ, or an equal blend of the 650 µ and 350 µ ground corn).All diets were prepared at New Fashion Pork's commercial feed mill in Estherville, IA.
Pigs were weighed and feed disappearance measured approximately every 2 weeks to calculate ADG, ADFI, and F/G.On d 87 of the trials, pens were weighed and the 6 heaviest pigs (selected by the marketing serviceman) were removed and transported 350 miles to Triumph Foods (St.Joseph, MO) for harvest.The remaining pigs were transported to Triumph Foods on d 101 for harvest.Pigs were weighed and feed disappearance was determined approximately every 21 d to calculate ADG, ADFI, and F/G.Yield was calculated using live weight at the farm and HCW at the plant.At the plant, backfat and loin depth were measured, and percentage lean was calculated using NPPC (1991) guidelines for lean containing 5% fat: Lean % = (2.83+ (0.469 × (HCW)) -(18.47 × (fat depth)) + (9.824 × loin depth))/(HCW).
Samples of corn and complete diets were collected during each phase.Particle size of corn samples and diets in meal form was determined using Tyler sieves (numbers 6, 8, 10, 14, 20, 28, 35, 48, 65, 100, 150, 200, 270, and a pan) and a Ro-Tap shaker (W.S. Tyler, Mentor, OH).One hundred-gram samples were sifted for 10 min without a flow agent, and the weight on each screen was used to calculate the mean particle size (Table 2).Pellet durability index (PDI) was determined using the standard tumbling-box technique, and modified PDI was done by adding 5 hexagonal nuts prior to tumbling.

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Percentage fines were also determined, and fines were characterized as material that would pass through a #6 sieve (3,360 µ opening).
Data were analyzed as a completely randomized design using PROC MIXED in SAS (SAS Institute, Inc., Cary, NC), with pen as the experimental unit.Treatments were analyzed as a 2 × 3 factorial with main effects of corn particle size and diet form.Linear and quadratic effects of decreasing particle size were determined as well as interactive effects of corn particle size and diet form.Results were considered significant at P < 0.05 and considered a trend at P < 0.10.

Particle size and pellet quality measurements
Particle size of corn was similar to expectations with corn targeted at 650 µ ranging from 616 to 681 µ and corn targeted at 350 µ ranging from 336 to 359 µ (Table 2).Because corn particle size of the diets containing a 50:50 mixture of 650 and 350 µ ground corns could not be determined, whole diet particle size was measured.These data found that whole diets of the 50:50 mixture were intermediate between high-and low-particle size corn diets, which was expected.High-quality pellets were produced as reflected by the PDI being greater than 90% and the percentage fines being 20% or less for all diets and phases.

Growth performance and carcass measurements
Overall (d 0 to 101), linear particle size × diet form interactions were observed (P < 0.02) for ADFI and F/G because ADFI decreased and F/G improved as particle size was reduced for pigs fed meal diets, but not for pigs fed pelleted diets (Table 3).Pigs fed pelleted diets had increased (P < 0.001) ADG and improved (P < 0.001) F/G.As corn particle size decreased, ADG and ADFI decreased (P < 0.02) linearly.Pigs fed pelleted diets had increased (P < 0.001) HCW compared with pigs fed meal diets, but no other effects (P > 0.12) on carcass characteristics were observed.
In summary, pigs fed pelleted diets had improved growth performance compared with those fed meal diets, with the greatest magnitude of F/G improvement to pellets occurring when pigs were fed 650-µ corn.Feed efficiency improved as corn particle size decreased for pigs fed meal diets but not for those fed pelleted diets, suggesting that grinding corn finer than 650 µ for pelleted diets conferred no benefit.Further research is needed to understand why F/G did not improve in pelleted diets as particle size was reduced from 650 to 350 µ.

Table 2 .
Analysis of pellet quality and particle size 1

Table 3 .
The effect of corn particle size and diet form (meal vs. pellet) on finishing pig performance 1