# [Pig Feed Particle Size](/knowledge/animal-farming/swine/pig-feed-particle-size-and-grinding-management) and Milling Controls ## Key Takeaways - Feed particle size is a critical feed-mill quality parameter directly influencing nutrient digestibility, feed intake, gut health, and manufacturing efficiency, with finer grinding improving starch digestion but increasing gastric ulcer risk below 300 µm. - Optimal particle size targets vary by production stage: transition pigs (339-534 µm), Initiation II (920-943 µm), and grow-finish pigs (500-700 µm), with geometric standard deviation ideally kept below 2.0 to minimize fines and oversize particles. - Routine sieve analysis using Ro-tap shakers and US standard sieves, reporting geometric mean diameter (dgw) and geometric standard deviation (Sgw), is essential for verifying targets and maintaining process control. - Excessively fine particles (<300 µm) increase the risk of gastric ulcers and esophageal lesions, while coarser particles (e.g., 600-900 µm with amylase-enriched corn) promote normal stomach keratinization and reduce ulcer incidence. - Feed flowability is significantly impacted by particle size, with very fine particles causing bridging in bins and reduced flow rates, whereas moderately coarse grinds improve handling in conveying systems. - Comprehensive record-keeping of dgw, Sgw, ingredient moisture, mill settings, and screen condition allows for troubleshooting performance deviations and tracing ulcer outbreaks to specific feed batches. --- [Swine feed particle size](/knowledge/animal-farming/swine/swine-feed-particle-size-effects-on-digestion-and-performance) is a feed-mill quality parameter that directly influences nutrient digestibility, feed intake, gut health, and manufacturing efficiency. The degree of grinding applied to cereal grains and protein meals determines the surface area available for enzymatic digestion, but it also affects gastric morphology, feed flow through handling equipment, and pellet quality. Feed-mill managers must establish particle size targets that balance biological performance with practical milling constraints, then verify those targets through routine sieve analysis and maintain records for process control and troubleshooting. ### At a Glance | Aspect | Key Points | |--------|------------| | Why particle size matters | Affects starch digestibility, feed efficiency, gastric lesion risk, and feed flowability. Finer grinding improves nutrient availability but may predispose pigs to gastric ulcers if particles are excessively small. | | Optimal ranges by stage | Transition (339,534 µm), Initiation I (339,534 µm in pellets, 305 µm in meal), Initiation II (920,943 µm), grow-finish (500,700 µm). Ranges differ by ingredient and feed form. | | Testing methods | Ro-tap sieve analysis with US standard sieves, geometric mean diameter (dgw) and geometric standard deviation (Sgw) reported. | | Gut-health implications | Excessively fine particles (<300 µm) increase risk of gastric ulcers and esophageal lesions. Coarse particles promote normal stomach keratinization and reduce ulcer incidence. | | Feed flow concerns | Very fine particles bridge in bins, reduce flow rate, and cause segregation. Moderately coarse grinds improve handling in augers, bins, and feeders. | | Record-keeping | Document dgw and Sgw per run, calibrations, screen condition, and ingredient moisture. Use records to trace performance deviations or ulcer outbreaks. | ## System Context and Planning Decisions ### Feed Mill as a Biological and Mechanical Interface The grinding step sits at the intersection of raw material variability and animal physiology. Corn, sorghum, soybean meal, and other ingredients differ in hardness, moisture, and starch composition. The mill's hammer-mill or roller-mill configuration, screen size, tip speed, and throughput all modulate the final particle size distribution. A mill manager's planning decisions must consider the targeted production stage because nursery pigs require a finer, more uniformly ground feed to maximize early starch digestion, whereas grow-finish pigs can utilize coarser particles without sacrificing performance and with less risk to stomach health. The 2026 literature review on ideal particle size confirms that optimal targets shift across stages, and that most studies evaluate mean particle size of a single ingredient instead of the full particle-strata distribution. ### Trade-offs Between Digestibility and Gut Health Fine grinding consistently improves feed conversion in young pigs because it exposes more starch to amylase action. However, the same fine particles reduce stomach fill, increase gastric emptying rate, and allow hydrochloric acid to contact the esophageal region of the stomach, leading to hyperkeratosis and ulceration. The 1995 study on particle size and pelleting in finishing pigs documented that finely ground, nonpelleted diets increased the incidence of stomach lesions. More recent Enogen Feed corn trials from 2021 and 2020 showed that when conventional yellow dent corn was ground to 300 µm, stomach ulceration was greater than at 600 or 900 µm, and that the α-amylase trait in Enogen did not eliminate the particle-size effect. These findings underscore that mill planning must incorporate a gut-health threshold, excessively fine grinding is not acceptable even if enzyme additives appear to improve digestibility. The Merck Veterinary Manual and USDA APHIS guidelines on gastric ulcer prevention recommend avoiding prolonged feeding of finely ground diets, particularly in meal form. ### Feed Form and Handling Infrastructure Pelleting adds another dimension. Fine particles compact more easily and produce durable pellets, but the pellet mill's conditioning temperature and die specifications also influence starch gelatinization. In mash diets, particle size directly dictates flowability. Very fine flour leads to bridging in bins, erratic feeder refill, and dust. Coarse particles flow freely but may segregate if the particle-size distribution is broad. The feed mill must coordinate grinding with the downstream conveying system: auger diameter, vertical drop distance, and bin geometry all affect whether a given particle size distribution will cause bridging or flooding. Records of feeder performance and bin flow issues should be used to adjust grinding targets. ## Core Management Framework ### Particle Size Targets by Production Stage The evidence-based targets provided by the 2026 literature review serve as a starting point. For transition pigs (weaning to approximately 7 kg), a geometric mean diameter of 339,534 µm is recommended, when feed is pelleted, the same range works, but for mash, a finer grind around 305 µm may be necessary to avoid sorting and to maintain intake. Initiation II (7,11 kg) tolerates a coarser grind at 920,943 µm. Grow-finish pigs from 25 kg to market can be fed corn ground to 500,700 µm. These targets are means, the geometric standard deviation should be kept below 2.0 to avoid excessive fines and coarse oversize particles. Every feed mill should establish its own baseline based on its ingredient supply and mill equipment, then verify with performance data and stomach morphology monitoring. ### Testing and Verification Particle size analysis must be performed on a routine schedule, also when a new corn variety arrives. A Ro-tap shaker with 13 or 14 US standard sieves (sizes from 4,700 µm down to 75 µm) is the industry standard. The procedure must follow ASAE S319.4 or ISO 2591-1. For each production shift, at least one sample per ingredient per mill should be taken. The results must be recorded as dgw and Sgw, along with the grinding date, ingredient lot, screen condition, and mill settings. This record set forms the basis for troubleshooting when pig performance drops or ulcer cases rise. When the geometric mean deviates by more than 50 µm from target, the mill operator should inspect screens for wear, adjust hammer speed or screen aperture, and re-sample. ### Gut-Health Considerations as a Control Limit Gastric ulceration remains a major cause of sudden death and reduced performance in finishing pigs. The 2020 and 2021 Enogen studies confirm that particle size independently influences stomach morphology, regardless of corn source or amylase activity. Therefore, particle size targets must include an upper limit on fines. A practical control is to ensure that no more than 10,15 percent of the sample passes through a 150 µm sieve. If fineness exceeds that threshold, the mill should either coarsen the grind or shift the feed to pellet form, because pelleting, despite containing ground material, reduces ulcer risk compared to fine mash. Records of stomach lesion prevalence at slaughter can be linked back to particle size logs to refine the mill's control limits. When ulcer incidence rises above normal baseline, the feed-mill manager and herd veterinarian should jointly review grinding records and consider a change in target particle size. ### Records for Continuous Improvement A feed mill's particle size database should include also the daily dgw and Sgw, but also ingredient moisture (which affects grindability and screen wear), mill amperage, and throughput rate. Over time, correlations between these parameters and nursery or finishing performance allow the mill manager to set dynamic targets. For example, high-moisture corn may require a smaller screen to achieve the same dgw as dry corn. Documenting these adjustments prevents drift and ensures repeatability. The USDA NAHMS swine studies have shown that feed-mill record-keeping is associated with fewer feed-related health incidents. Regularly archiving sieve results in a spreadsheet or logbook creates an audit trail for regulatory inspections and for internal quality audits. When a new ingredient arrives, the mill can test its grind profile before committing to a production run. Consultation with a swine nutritionist or extension specialist is warranted when transitioning between corn sources, when changing mill equipment, or when stomach ulcer prevalence exceeds historical levels. Particle size management is not static, it requires periodic review of both the mill's capability and the herd's biological response. ## Feed-Mill Quality Control and Particle Size Analysis Consistent particle size management begins with accurate measurement. The standard method for determining particle size in swine feeds uses a sieve shaker to separate a representative sample into size fractions, from which the geometric mean diameter and standard deviation are calculated. This procedure, defined in ASAE S319.2, provides the basis for setting grinding targets and evaluating mill performance. A single mean particle size value is insufficient, the distribution of particle sizes, expressed as the geometric standard deviation, influences both digestibility and feed handling. Excessive variability indicates inconsistent mill operation or worn screens and rolls. Routine sampling at the mill discharge and at the feeder ensures that the delivered feed matches the spec. Without regular testing, deviations accumulate and undermine the economic value of precision grinding. The 2017 review on feed structure in pig nutrition emphasizes that both mean particle size and distribution must be controlled to optimize nutrient utilization and minimize gastric lesions __MASK_1__. Feed mills serving swine operations should maintain a log of particle size results per batch, identifying trends before they cause performance loss. ## Feed Flow and Handling Consequences Particle size directly affects the physical properties of feed. Fine particles, particularly those below 300 microns, increase bridging and ratholing in bulk bins, reduce flow rate through feeders, and promote segregation of ingredients during transport. Coarse particles flow more freely but may separate from fines in a feed line, leading to inconsistent nutrient delivery within a pen. The 2017 review notes that fine grinding increases the surface area and bulk density of the feed, which can reduce the volume of feed delivered per auger revolution and increase energy consumption during pelleting. Conversely, excessively coarse feed may cause incomplete mixing and larger variations in nutrient concentration at the feeder. These flow issues are particularly problematic in automated feeding systems where bridging leads to unintended feed restriction and uneven growth. Regular observation of feed flow at the bin discharge and at the trough, combined with particle size data, allows the mill manager to adjust grind settings to balance handling and nutritional goals. ## Gut Health and Stomach Morphology The relationship between particle size and gastric health is well established. Finely ground feed, especially when pelleted, reduces the time feed spends in the stomach and alters the pH environment in the pars esophagea, increasing the risk of hyperkeratinization and ulceration. A 1995 study on finishing pigs reported that fine grinding and pelleting reduced stomach ulcer scores compared to coarse mash, but this benefit was offset by a higher incidence of ulceration in pigs fed fine pellets __MASK_2__. More recent work with Enogen Feed corn, which contains an alpha amylase enzyme trait, demonstrates that corn source interacts with particle size. In nursery and finishing pigs, Enogen corn ground to 600 microns supported growth performance equal to conventional corn ground to 300 microns, while reducing the severity of stomach lesions associated with fine grinding __MASK_3__. The same pattern appeared in a finishing study where pigs fed Enogen corn at 600 and 900 microns had similar average daily gain and feed efficiency compared to those fed conventional corn at 300 microns, with fewer gastric ulcers __MASK_4__. These findings indicate that selecting a corn variety with higher starch digestibility allows for coarser grinding without sacrificing feed conversion, thereby protecting gut integrity. Pig producers should monitor stomach lesion scores at slaughter as a direct indicator of particle size appropriateness. ## Production-Stage Decisions Grinding targets must be adjusted across the pig's life cycle. A 2026 literature review concluded that for transition pigs, the optimal ingredient particle size falls between 339 and 534 microns __MASK_5__. For initiation phase I pigs, a similar range applies when feed is pelleted, but if fed as meal, a finer target of 305 microns is recommended to support digestibility. For initiation phase II, the review suggests a coarser target of 920 to 943 microns. During the grow finish period, a target of 500 to 700 microns balances digestibility with gastric health. These figures represent mean particle size, the distribution should remain narrow. When pelleting, the additional heat and pressure further improve starch gelatinization, which may allow slightly coarser grinding than for mash. The 2017 review confirms that pelleting can mitigate the negative effects of coarse particles on digestibility, but pelleting fine particles increases the risk of ulcer formation. Producers should therefore match particle size to feed form. For operations using multiple grain sources, the optimal particle size of each ingredient must be evaluated separately because corn, sorghum, and soybean meal differ in starch structure and protein matrix, affecting grinding response. ## Records and Monitoring A particle size control program requires systematic record keeping. Each mill batch should have a documented target mean particle size, actual result from sieve analysis, and the standard deviation. Changes in screen condition, hammer tip wear, or roll gap settings should be logged with date and particle size data. At the farm level, weekly records of feed flow, feed intake per pen, and body weight gain allow correlation with particle size changes. Stomach lesion scores collected from cull pigs or at slaughter provide biological validation. The USDA NAHMS program and WOAH terrestrial code emphasize monitoring production inputs that affect animal health, and particle size is a quantifiable input that directly influences gastric disease risk __MASK_6__ and __MASK_7__. A trend of increasing stomach lesions should prompt immediate particle size analysis and adjustment. ## Welfare, Worker Safety, and Food Safety Fine grinding compromises pig welfare through increased incidence of gastric ulcers, which cause pain, inappetence, and reduced performance. The Merck Veterinary Manual notes that ulceration in swine is multifactorial but that feed particle size is a key modifiable factor. Coarse grinding reduces ulcer risk but may lower digestibility, requiring careful management of feed processing. Worker safety is affected by dust generated during grinding and handling. Fine feed particles create respirable dust that can cause respiratory irritation and increase explosion hazard in feed mills. Dust control measures, including aspiration at grinders and pellet coolers, are essential. Food safety considerations include the potential for mycotoxin concentration in fine particles if contaminated grain is ground excessively. Mycotoxins are often concentrated in smaller kernel fractions, fine grinding distributes them throughout the feed, increasing exposure risk. Producers should screen ingredients for mycotoxins before grinding and adjust particle size to minimize concentration of contaminated fines. ## Failure Patterns and Practical Monitoring Common failure patterns include grinding too fine to maximize digestibility, leading to ulcers and feed bridging, or grinding too coarse to reduce mill energy costs, causing poor feed conversion. Inconsistent particle size from worn equipment produces variable animal performance within a herd. Practical monitoring involves daily visual inspection of feed texture, weekly sieve analysis, and routine collection of stomach lesion data at slaughter. If lesions exceed benchmarks, the next step is to adjust the mill target upward by 100 microns and reassess after two feeding cycles. The Enogen studies demonstrate that using high digestibility corn allows a coarser target without performance loss, providing a straightforward intervention. Feed mills should also monitor energy consumption per tonne, an unexplained drop may indicate reduced grinding resistance from worn screens, leading to coarser particles. Correlation of mill data with farm records completes the feedback loop. The FAO Animal Production and Health guidelines recommend integrating feed processing parameters into overall herd health monitoring to anticipate nutritional problems before they affect production __MASK_8__. By treating particle size as a quality control metric governed by objective measurement and regular record review, the swine industry can reduce gastric disease, improve feed efficiency, and enhance worker safety without sacrificing digestibility. ## Health Observation and Gut Integrity Fine grinding improves starch digestibility but imposes measurable risks to swine gastric health. The 1995 study on particle size and stomach morphology documented increased incidence of gastric hyperkeratosis and ulceration when pigs received corn ground to less than 500 microns (Effects of particle size and pelleting on growth performance, nutrient digestibility, and stomach morphology in finishing pigs). This finding has been replicated across multiple production stages. The Enogen Feed corn trials from 2020 and 2021 reported that pigs fed corn ground to 300 microns exhibited greater severity of stomach lesions compared with pigs fed 600 or 900 micron corn (Influence of Particle Size of Enogen Feed High Amylase and Conventional Yellow Dent Corn on Finishing Pig Performance, Carcass Characteristics, and Stomach Ulceration, 133 Influence of Particle Size of Enogen Feed Corn and Conventional Yellow Dent Corn on Nursery and Finishing Pig Performance, Carcass Characteristics and Stomach Morphology). The interaction between corn source and particle size was significant for feed efficiency in some studies, but stomach morphology changes were consistently driven by particle size instead of amylase activity. Producers and feed mill managers must recognize that ulceration risk increases when mean particle size falls below 500 microns, especially in mash diets. Pelleted diets may reduce this risk slightly because the pelleting process agglomerates fines, but the underlying particle size distribution remains critical. Routine slaughter checks or post-mortem examination of stomachs from culled or deceased pigs should include assessment of the esophageal region for parakeratosis, erosion, or ulceration. The Merck Veterinary Manual provides guidance on diagnosing gastric ulcers in swine, noting that affected pigs may exhibit pallor, melena, reduced feed intake, and sudden death (Merck Veterinary Manual). When such signs appear, immediate review of feed particle size data and grinding equipment maintenance records is warranted. ### Biosecurity Considerations in Milling Particle size influences the ability of feed milling processes to inactivate or reduce pathogens. Smaller particles increase surface area, which can improve heat penetration during conditioning and pelleting. However, the relationship is not linear, very fine particles may create dust that disperses pathogens within the mill environment. The FAO Animal Production and Health guidelines on feed hygiene emphasize that particle size uniformity is essential for achieving consistent thermal processing (FAO Animal Production and Health). Coarse or uneven particle size can shield pathogens from heat, reducing the lethality of steam conditioning. The WOAH Terrestrial Animal Health Code includes recommendations for feed mill biosecurity, such as maintaining clean ingredient flows and avoiding cross-contamination between raw materials and finished feed (WOAH Terrestrial Animal Health Code). Particle size control is not a direct biosecurity measure but supports effective heat treatment and reduces the risk of feed segregation. When grinding equipment is poorly maintained, particle size variability increases, which can compromise the uniformity of moisture and temperature during pelleting. Mills producing feed for swine should monitor particle size distribution as part of their Hazard Analysis and Critical Control Point (HACCP) plans. ### Diagnostic and Veterinary Escalation Veterinarians investigating herd health problems that include reduced growth, variable feed intake, or increased mortality should consider feed particle data as part of the diagnostic workup. A sudden change in particle size often occurs after hammer mill screen changes, wear of rollers, or errors in mill settings. Diagnostic steps include collecting representative feed samples from multiple feeders, performing sieve analysis (such as using the ASABE S319 method), and comparing results to the target particle size for the production stage. When gastric ulcers are confirmed, immediate escalation involves verifying that the mean particle size meets the recommended range for that age group. For nursery pigs, the literature review from 2026 identifies an optimal range of 339 to 534 microns, but this applies to corn and sorghum in pellet or meal form (Ideal particle size in the main ingredients in pig feed). Finishing pigs tolerate and benefit from larger particle sizes of 500 to 700 microns. If particle size is found to be too fine, the feed mill must replace screens or adjust roller mill gap. In severe cases, adding a coarse grain source or using a coarser grind for a period may allow stomach healing. Uncertainty exists because most studies evaluate only the mean particle size of a single ingredient, ignoring the particle size distribution of the complete diet. The 2026 review notes this as a limitation (Ideal particle size in the main ingredients in pig feed). Furthermore, interactions between particle size, feed form (mash vs. pellet), and ingredient amylase content are incompletely understood. The Enogen Feed corn studies showed that at 300 microns, the amylase trait did not worsen stomach morphology, but performance benefits were inconsistent. Veterinarians should interpret published targets as guidelines instead of thresholds, and adjust based on observed herd response and feed mill capability. ### Sustainability Implications Optimizing particle size contributes to sustainability in two ways: feed efficiency and energy use in milling. Finer grinding increases starch digestibility, reducing the amount of feed needed per unit of gain, which lowers the environmental footprint per pig produced. However, excessive fine grinding increases electrical energy consumption at the mill and accelerates wear on screens and hammers. The net sustainability effect depends on balancing the energy cost of grinding against the feed cost savings. The review on feed structure emphasizes that coarse grinding (above 700 microns) wastes digestibility, while extreme fine grinding (below 300 microns) wastes energy and harms pig health (Importance of feed structure (particle size) and feed form (mash vs. pellets) in pig nutrition , A review). From a herd health perspective, reducing ulcer incidence through appropriate particle size also improves sustainability by decreasing mortality, veterinary costs, and the need for medical treatments. USDA NAHMS data indicate that stomach ulcers are a relatively common finding in finishing swine at slaughter, and many are subclinical (USDA National Animal Health Monitoring System). Preventing these lesions through feed mill quality control is a cost-effective intervention. ## Frequently Asked Questions **1. What particle size is safest for preventing stomach ulcers in finishing pigs?** A mean particle size of 500 to 700 microns for corn-based diets is recommended for finishing pigs. Below 500 microns, risk of ulceration increases markedly. **2. How often should feed particle size be tested in a swine operation?** At minimum, test after any equipment change or screen replacement, and monthly for routine quality assurance. More frequent testing is warranted if growth performance or health indicators change. **3. Does pelleting change the effective particle size?** Pelleting agglomerates particles but does not alter the underlying grind. The particle size distribution of the mash that goes into the pellet mill is the critical control point. **4. Can particle size influence feed intake in nursery pigs?** Yes, very fine particles can reduce feed intake due to poor palatability and increased dustiness. The optimal range is 339 to 534 microns for pelleted nursery diets. **5. What is the best method for measuring particle size on farm?** Sieve analysis using a set of standard sieves (Ro-Tap or equivalent) is the most reliable method. Hand sieving is less accurate but can provide rapid estimates. **6. Are there differences in optimal particle size between corn and sorghum?** Sorghum generally requires slightly finer grinding than corn to achieve similar starch digestibility, but the same general ranges apply. The 2026 review indicates that optimal particle size for sorghum in nursery diets is similar to corn. **7. How does amylase-enriched corn affect particle size recommendations?** Current evidence suggests that amylase corn does not allow coarser grinding. The benefit in starch digestibility is additive to the effect of reducing particle size, not a substitute for it. **8. What should a producer do if stomach ulcers are suspected?** Contact a veterinarian immediately to confirm the diagnosis and review feed particle data. Switch to a coarser grind (above 600 microns) while the herd is investigated. ## Educational Veterinary Notice The information provided here is intended for educational purposes in the context of swine feed milling and herd health management. Feed particle size recommendations should be adapted to specific herd conditions, ingredient sources, and mill capabilities. Always consult a licensed veterinarian for diagnosis and treatment of animal health problems, and work with a qualified nutritionist or feed mill professional to adjust particle size targets. Routine monitoring of stomach health at slaughter is a valuable tool for assessing the adequacy of feed milling practices. ## Related Farming Guides - __MASK_9__ - __MASK_10__ - __MASK_11__ - __MASK_12__ - __MASK_13__ ## Related Clinical & Scientific Guides * [Pig Enrichment Programs and Behavior Monitoring](/knowledge/animal-farming/swine/pig-enrichment-programs-and-behavior-monitoring) * [Swine Handling Facility Design for Safe Pig Movement](/knowledge/animal-farming/swine/swine-handling-facility-design-safe-pig-movement) * [Swine Feeding Management for Grow-Finish Pigs](/knowledge/animal-farming/swine/swine-feeding-management-for-grow-finish-pigs) ## References and Further Reading - __MASK_14__ - __MASK_15__ - __MASK_16__ - __MASK_17__ - __MASK_18__ > This article is educational and is not a substitute for veterinary diagnosis, treatment, public-health guidance, or regulatory reporting.