# Swine Feed Particle Size: Effects on Digestion and Performance ## Key Takeaways - Optimal particle size for grow-finish pigs on corn-soy diets is 650-750 microns, balancing improved nutrient digestibility (especially starch and protein) with reduced risk of gastric ulcers. Particles below 500 microns significantly increase ulcer incidence due to inadequate protective stomach mat formation. - Gestating and lactating sows benefit from coarser diets (700-900 microns) to mitigate ulcer risk and improve feed intake, as coarser particles slow consumption and enhance satiety. - Nursery pigs require finer particles (500-600 microns) to maximize nutrient absorption due to immature digestive systems, but this necessitates careful feeder management to prevent issues like vomiting and reduced intake. - Particle size uniformity, measured by Geometric Standard Deviation (GSD), is critical; a GSD below 2.0 indicates a desirable narrow particle distribution, minimizing the negative impacts of both overly fine particles (ulcers, dust) and coarse particles (reduced digestibility). - Accurate measurement via sieve analysis (ASABE S319 standard) is essential, with regular monitoring (monthly baseline) of both average particle size and GSD to detect equipment wear or process deviations impacting feed efficiency and pig health. - Overly fine grinding (<500 microns) leads to increased dust, poor feed flow, and a high incidence of gastric ulcers, while overly coarse grinding (>900 microns) results in reduced nutrient digestibility and feed efficiency, directly impacting profitability. --- Getting feed particle size right is one of the most cost-effective adjustments you can make in a swine operation, yet it is often overlooked. This guide explains how particle size affects digestion, growth performance, nutrient utilization, and stomach health in grow-finish pigs, breeding stock, and young pigs. It provides practical steps for measuring particle size, adjusting your grinding equipment, avoiding common mistakes, and deciding when to call in professional help. This article is written for farm owners, herd managers, feed mill operators, and anyone responsible for pig performance and feed efficiency. ## At a Glance - **Optimal range for corn-soy diets:** 650 to 750 microns for grow-finish pigs. This range balances feed efficiency and stomach health. - **Do not grind too fine:** Particles below 500 microns increase the risk of gastric ulcers and bridging in feed bins and feeders. - **Do not grind too coarse:** Particles above 900 to 1000 microns reduce digestibility and feed efficiency, costing you money in wasted feed. - **Sows perform well on coarser diets:** Gestating and lactating sows can be fed at 700 to 900 microns to reduce ulcer risk and improve feed intake. - **Nursery pigs need finer particles:** Starter diets at 500 to 600 microns improve digestibility in young pigs, but watch feeder management carefully. - **Measure, do not guess:** Use a 13-screen particle size sieve set or a commercial particle size analyzer to know what you are actually feeding. - **Check uniformity:** A good grind has a geometric standard deviation (GSD) below 2.0. A high GSD means too many fine and coarse particles mixed together. - **Review your mill regularly:** Hammer mill screen size, roller mill settings, and moisture content all affect particle size. Calibrate and inspect equipment on a schedule. - **Monitor performance:** Track feed conversion, average daily gain, and stomach lesions at slaughter to catch particle size problems early. ## Why Particle Size Matters in Swine Diets Particle size is the average diameter of the ground feed particles in a diet. When you grind grain, you increase the surface area available for digestive enzymes to act on. Smaller particles are digested more quickly and completely in the stomach and small intestine. Larger particles pass through more of the digestive tract undigested, which means you are spending money on feed that the pig cannot fully use. The relationship between particle size and digestibility is not linear. Grinding finer improves digestibility up to a point, then the benefits shrink and the risks grow. Very fine particles increase dust, reduce feed flow, and are linked directly to gastric ulcers in pigs. The goal is to find the sweet spot where you get most of the digestibility benefit without causing stomach damage or feed handling problems. Feed cost is the largest single expense in swine production, typically 60 to 75 percent of total production costs. Improving feed efficiency by even 2 to 3 percent through better particle size management can have a significant impact on your bottom line across a year of production. This is why particle size deserves attention as a management tool, not just a feed mill detail. ## The Science of Particle Size and Digestion ### How Particle Size Affects Nutrient Breakdown When a pig eats feed, the stomach and small intestine work to break down starches, proteins, and fats into forms the body can absorb. Enzymes in the digestive tract act on the surface of feed particles. Smaller particles expose more surface area per unit of weight, so enzymes can work faster and more completely. Starch is the main energy source in corn-based swine diets. The digestibility of starch improves as particle size decreases. Studies have consistently shown that reducing corn particle size from about 1000 microns to 700 microns improves energy digestibility by roughly 3 to 5 percent. This translates directly into better feed conversion and faster growth. Protein digestibility also improves with finer grinding, although the effect is smaller than for starch. Amino acids are better absorbed when the protein matrix of the grain is broken down more completely. This means you may be able to reduce dietary protein levels slightly when particle size is optimal, saving money on expensive amino acid supplements. ### The Stomach Health Tradeoff The pig stomach is a simple stomach, similar to a human stomach, and it is vulnerable to ulceration when feed is too fine. Fine particles create a more fluid stomach content that does not form a protective mat at the top of the stomach. This allows acidic stomach juices to contact the unprotected esophageal region of the stomach lining, leading to inflammation and ulcers. Gastric ulcers are a serious economic problem in swine herds. They cause reduced feed intake, slower growth, and sudden death in severe cases. At slaughter, ulceration rates of 10 to 30 percent are common in herds fed finely ground diets. The economic loss comes from both reduced performance in the live pig and condemnation of stomachs at the packing plant. The scientific evidence strongly supports keeping particle size above 600 to 650 microns for grow-finish pigs specifically to reduce ulcer risk. The tradeoff is clear: finer grinding improves digestibility but increases ulcer risk. The optimal range of 650 to 750 microns represents the practical balance between these two competing effects. ### Particle Size Uniformity Average particle size is only part of the story. The uniformity of the grind matters just as much. A feed with a geometric standard deviation (GSD) above 2.0 contains a wide mix of very fine and very coarse particles. The fine particles increase ulcer risk and dust, while the coarse particles reduce digestibility. You get the worst of both worlds. A well-ground feed should have a GSD below 2.0, and ideally below 1.8. This means most particles are close to the average size. Uniform grinding allows pigs to sort feed less, reduces dust in the barn, and keeps the ration consistent from batch to batch. Roller mills generally produce a more uniform grind with a lower GSD than hammer mills. Hammer mills produce more fine particles and more variation. However, both types of mills can produce acceptable feed if they are properly adjusted and maintained. The key is to measure your output regularly and adjust accordingly. ## Optimal Particle Size by Pig Class ### Grow-Finish Pigs For growing and finishing pigs from about 50 pounds to market weight, the optimal particle size range is 650 to 750 microns for corn-based diets. This range has been confirmed by decades of research and practical experience in commercial swine operations. Within this range, you can fine-tune based on your specific conditions. Pigs in the early grow phase benefit from slightly finer grind around 650 to 700 microns because their digestive systems are still developing. Finishing pigs can be fed slightly coarser at 700 to 750 microns to reduce ulcer risk during the final weeks before market. The economic benefit of staying in this range is substantial. Compared to feeding a coarse grind above 900 microns, you can expect an improvement in feed conversion of 5 to 7 percent. Compared to an overly fine grind below 500 microns, you reduce ulcer risk and associated mortality and morbidity. ### Nursery Pigs Weaned pigs have immature digestive systems and benefit from finer particle sizes to maximize nutrient digestibility. Starter diets are typically ground to 500 to 600 microns. The higher digestibility helps young pigs overcome the stress of weaning and get off to a strong start. However, nursery pigs are also at higher risk for ulcers when feed is too fine. Feeder management becomes critical at this stage. Ensure feed flows freely, avoid stale feed buildup in feeders, and monitor for signs of reduced intake or vomiting, which can indicate stomach irritation. As pigs move from nursery to grow-finish diets, gradually transition particle size upward over a period of 7 to 10 days. A sudden change in feed texture can reduce intake and cause digestive upset. ### Sows and Boars Breeding stock should be fed coarser diets than growing pigs. A particle size of 700 to 900 microns is appropriate for gestating and lactating sows. The coarser grind helps maintain stomach health during the stress of gestation and lactation. Sows are often limit-fed during gestation, which means they consume their daily ration quickly. Coarser particles slow the rate of intake slightly and help the sow feel fuller. During lactation, sows need high feed intake to support milk production, and a coarser grind can help prevent the stomach issues that come with very fine diets. There is also evidence that feeding sows coarser diets improves fiber utilization and helps maintain gut health through the reproductive cycle. This can translate into better litter performance and longer productive life for the sow. ## Measuring Particle Size ### The Sieve Method The standard method for measuring particle size is the dry sieve analysis using a set of stacked screens. The American Society of Agricultural and Biological Engineers (ASABE) has established a standard method for this analysis, commonly referred to as ASABE S319. You will need a sieve set with 13 screens, typically ranging from 4750 microns down to 45 microns, plus a pan at the bottom. The screens are stacked in descending mesh size, with the largest openings at the top. A representative feed sample of about 100 grams is placed on the top screen, and the stack is shaken for a set period, usually 10 minutes, using a mechanical sieve shaker. After shaking, the weight of feed retained on each screen is recorded. These weights are used to calculate the geometric mean particle diameter and the geometric standard deviation. The geometric mean is reported in microns and represents the average particle size. The geometric standard deviation indicates the uniformity of the grind. ### Sampling Procedures Accurate results depend on proper sampling. Take feed samples from the finished feed stream, not just from the top of a bin or feeder. The best sampling point is where feed is being loaded into the bin or transported to the barn. Collect several small samples over time rather than one large grab sample. A good approach is to take a handful of feed every few minutes during the loading process and combine these into one composite sample for analysis. This gives a more representative picture of the whole batch. If you are sampling from a feeder in the barn, take samples from several different feeders and from different depths within each feeder. Pigs sort feed, so the particle size at the top of a feeder can be different from what is at the bottom. The sample you analyze should represent what the pigs are actually eating. ### Interpreting Results Once you have the geometric mean particle size and GSD, compare them to your target range for each pig class. If the average is too coarse, you need to grind finer. If it is too fine, you need to adjust your mill settings to produce a coarser grind. A GSD above 2.0 indicates a uniformity problem. This often happens when a hammer mill screen is worn, when the mill is overloaded, or when the mill is not properly maintained. Roller mills can also produce variable results if the rolls are worn or the gap is not set correctly. Do not rely on a single measurement. Particle size can vary between batches and even within a batch. Establish a regular testing schedule, at least monthly for most operations, and track the results over time. This will help you spot trends and catch equipment problems before they cost you money. ## Adjusting Grinding Equipment ### Hammer Mill Adjustments Hammer mills are the most common grinding equipment on swine farms. They work by impacting grain with rapidly rotating hammers that break the grain against a perforated screen. The particle size is primarily controlled by the screen opening size. To grind finer, use a screen with smaller openings. To grind coarser, use a screen with larger openings. The relationship between screen size and final particle size is not exact, but as a general guide, a screen with 3/16-inch openings will produce feed in the 700 to 800 micron range for corn. A 1/8-inch screen will produce finer feed around 500 to 600 microns. Several other factors affect hammer mill performance. The tip speed of the hammers matters, with higher speeds producing finer particles. The condition of the hammers is critical, worn hammers are less efficient and produce more variable particle sizes. The rate of feed entering the mill also affects particle size, overloading the mill produces coarser, less uniform feed. Regular maintenance of your hammer mill is essential. Check hammers for wear and rotate or replace them according to the manufacturer recommendations. Inspect screens for holes, tears, or wear that can let oversized particles through. Keep the mill area clean and free of debris that can damage equipment. ### Roller Mill Adjustments Roller mills produce a more uniform grind than hammer mills and use less energy. They work by passing grain between two counter-rotating rolls. The particle size is controlled by the gap between the rolls and the differential speed between them. To adjust particle size on a roller mill, change the roll gap. A smaller gap produces finer particles. The roll gap should be checked regularly and adjusted as the rolls wear. You may need to adjust the gap differently at the center of the rolls compared to the ends, as rolls tend to wear more in the center. Roller mills require more careful management than hammer mills. The grain must be clean and free of foreign material that can damage the rolls. The rolls need to be kept properly aligned, and the differential speed needs to be maintained. Regular inspection and maintenance are essential for consistent performance. ### Factors That Affect Grinding Efficiency Moisture content has a significant effect on grinding. Grain that is too wet, above 16 percent moisture, grinds poorly and produces more fines and more variation. Grain that is too dry, below 12 percent moisture, can be dusty and may produce more fine particles than desired. The type of grain also matters. Corn is relatively easy to grind, while wheat and barley can be more challenging due to their different physical characteristics. If you are grinding multiple grain types, you may need to adjust your mill settings for each one. The capacity of your grinding system affects particle size consistency. If you push more grain through the mill than it can handle, particle size becomes more variable and the mill may not achieve the target grind. Match your grinding rate to your mill capacity and avoid overloading. ## Common Particle Size Mistakes ### Grinding Too Fine The most common mistake in swine feed particle size management is grinding too fine. Many producers believe that finer grinding always means better feed efficiency. This is true up to a point, but the risks of fine grinding quickly outweigh the benefits. When particle size drops below 500 to 550 microns, the risk of gastric ulcers increases substantially. Feed also becomes dusty, which can cause respiratory irritation in both pigs and workers. Fine feed flows poorly in bins and feeders, creating bridging and flow problems that reduce feed intake. The performance loss from fine grinding is often hidden. Pigs may look normal but gain more slowly and convert feed less efficiently because they are eating less due to stomach discomfort. The full cost of fine grinding may only show up at slaughter when stomach lesions are found. ### Grinding Too Coarse The opposite mistake is grinding too coarse. Producers who are worried about ulcers may overcorrect and feed a very coarse grind above 900 to 1000 microns. This reduces digestibility and feed efficiency, costing money in wasted feed. Coarse particles pass through the digestive tract largely undigested. This is especially true for corn, where the starch inside the kernel is protected by a tough outer coating that is difficult for pigs to break down. The result is more manure, more nutrient excretion, and poorer feed conversion. The cost of coarse grinding is often underestimated because it is less dramatic than the health problems of fine grinding. But the financial impact is real. A 5 percent reduction in feed efficiency on a farm feeding 10,000 pigs per year can cost tens of thousands of dollars annually. ### Ignoring Uniformity Some producers focus only on average particle size and ignore uniformity. This is a mistake. A feed with a high GSD contains both very fine and very coarse particles, and you get the disadvantages of both. The fine particles increase ulcer risk and dust. The coarse particles reduce digestibility. Pigs may also sort the feed, eating the fine particles first and leaving the coarse particles, which further reduces digestibility and creates waste. Measuring GSD is just as important as measuring average particle size. If your GSD is above 2.0, address the underlying equipment or management issue before worrying about fine-tuning the average particle size. ### Not Measuring at All The biggest mistake of all is not measuring particle size. Many producers set their mill and never check the output. They assume that because the mill is set a certain way, the feed is the right particle size. This assumption can be wrong. Screens wear, hammers wear, rolls wear, and grain moisture changes. All of these factors affect particle size. Without regular measurement, you are flying blind. You may be feeding a grind that is far from optimal without knowing it. Invest in a sieve set and a shaker, or establish a relationship with a lab that can do particle size analysis for you. The cost is small compared to the potential savings in feed efficiency and the reduction in ulcer-related losses. ## Decision Thresholds for Particle Size Adjustment ### When to Grind Finer Consider grinding finer when you observe any of the following: - Feed conversion is poorer than expected for your genetic line and stage of production - Average daily gain is below targets - Fecal material contains visible whole or partially intact grain particles - Particle size measurements show a geometric mean above 850 to 900 microns for grow-finish diets If you are currently feeding a coarse grind above 900 microns, moving down to 700 to 750 microns should improve feed efficiency by 3 to 5 percent. This improvement alone can pay for the cost of particle size management many times over. ### When to Grind Coarser Consider grinding coarser when you observe any of the following: - Particle size measurements show a geometric mean below 550 to 600 microns for grow-finish diets - Gastric ulcers are diagnosed at slaughter, with more than 5 to 10 percent of stomachs affected - Pigs are vomiting, especially after eating - Feed is bridging in bins or feeders, causing inconsistent intake - Dust levels in the barn are high enough to be visible in the air If you are feeding below 550 microns, move up to 650 to 700 microns. This may slightly reduce digestibility, but the improvement in stomach health and feed intake should more than compensate. ### When to Adjust Uniformity Consider addressing uniformity when: - Geometric standard deviation is above 2.0 - You see a wide range of particle sizes when you look at a feed sample - Pigs are sorting feed in the feeder, leaving coarse particles behind - You are using a hammer mill with worn screens or hammers Improving uniformity often requires equipment maintenance or changes. If you are using a hammer mill, consider whether a roller mill would produce more consistent results for your operation. ### When to Review Your Entire Feed Program Sometimes particle size is not the root cause of poor performance. If you have confirmed that particle size is in the optimal range but pigs are still underperforming, look at other factors: - Feed ingredient quality and nutrient content - Feed intake and water availability - Barn environment, including temperature and ventilation - Health status and disease pressure - Genetics and expected performance levels A systematic approach to troubleshooting will help you identify the real issue rather than making unnecessary changes to particle size. ## Monitoring and Recordkeeping ### Establishing a Particle Size Testing Schedule Set a regular schedule for particle size testing. Monthly testing is a good baseline for most operations. If you have recently changed equipment, ingredients, or mill settings, test more frequently until you confirm consistent results. Keep records of every particle size test. Record the date, the batch or lot number, the geometric mean particle size, the GSD, and any notes about equipment settings or conditions. This record will help you spot trends and identify when something has changed. ### Tracking Performance Metrics Particle size is a means to an end. The real goals are feed efficiency, growth rate, and stomach health. Track these metrics alongside your particle size data. Feed conversion is the most important metric to monitor. Calculate it for each group of pigs from weaning to market, or for each phase of production. Compare your results to your targets and to historical performance. Average daily gain is another key metric. Track it by group and by phase. If growth slows while feed intake stays the same, digestibility may have declined, which can point to a particle size problem. ### Monitoring Stomach Health at Slaughter If you market pigs through a packing plant, ask about stomach lesion checks. Many plants can provide feedback on the percentage of stomachs with ulcers or lesions. This information is valuable for confirming that your particle size program is protecting stomach health. Aim for less than 5 percent of stomachs with severe lesions. If you see more than this, consider whether your particle size is too fine or your GSD is too high. Even if average particle size is in the optimal range, a uniformity problem can still cause stomach issues. ### Keeping Equipment Logs Maintain a log for each piece of grinding equipment. Record screen sizes, hammer condition, roll gaps, and any maintenance performed. This log will help you understand how equipment changes affect particle size and will remind you when maintenance is due. Review equipment logs regularly to identify patterns. For example, if particle size tends to drift coarser after a certain number of tons have been ground, you may need to schedule maintenance more frequently. ## When to Call a Veterinarian or Extension Agent ### Signs That Require Veterinary Attention If you see signs of gastric ulcers or other stomach problems in your pigs, contact your veterinarian. These signs include: - Vomiting, especially after eating - Pale skin or pale mucous membranes, which can indicate internal bleeding - Sudden death, especially in grow-finish pigs - Reduced feed intake across a group of pigs - Dark, tarry feces that indicate digested blood in the digestive tract Gastric ulcers can be fatal, and sudden death is not uncommon in severe cases. Do not wait to call your veterinarian if you suspect ulcers are causing death losses. Your veterinarian can help you confirm the diagnosis, treat affected pigs, and advise on management changes to prevent further cases. They can also work with you to rule out other causes of the signs you are seeing. ### When to Contact an Extension Agent or Nutritionist Your local agricultural extension agent or a swine nutritionist can help with the more technical aspects of particle size management. Consider reaching out when: - You are setting up a new grinding system and need guidance on equipment selection - You want to establish a particle size testing program and need help interpreting results - You are considering changing from a hammer mill to a roller mill or vice versa - You want a feed efficiency audit to identify opportunities for improvement - You are experiencing performance problems that you cannot explain with your current data Extension agents and nutritionists have access to research-based information and can help you apply it to your specific operation. They can also help you compare your operation to industry benchmarks and identify areas for improvement. ### Working with Your Feed Supplier Your feed supplier can be a valuable resource for particle size management. Many commercial feed mills offer particle size analysis as part of their services. If you buy complete feed or concentrate, ask your supplier about their particle size specifications and quality control procedures. If you grind on-farm, your feed supplier may still be able to help with ingredient quality and ration formulation. They can also provide guidance on how particle size interacts with other feed factors such as enzyme use and ingredient selection. ## Practical Steps for Implementing a Particle Size Program ### Step 1: Assess Your Current Situation Start by measuring your current particle size. Take samples from every feed line and every pig class. Run the analysis and record the results. This gives you a baseline to work from. Also review your current equipment and maintenance practices. When was the last time you checked hammers or screens? When was the last time you calibrated your roller mill? Are you following the manufacturer recommended maintenance schedule? ### Step 2: Set Targets Based on your pig classes and production goals, set particle size targets. Use the ranges provided in this guide as a starting point, but adjust based on your specific conditions and experience. Write down your targets and share them with everyone involved in feed production and feeding. Make sure everyone understands why particle size matters and what the targets are. ### Step 3: Adjust Equipment Make the necessary adjustments to your grinding equipment to hit your targets. This may involve changing screens, adjusting roll gaps, or repairing worn parts. Take the time to do this properly, and verify the results with a particle size test. If you are making large changes, do not try to do everything at once. Make one adjustment at a time and measure the results. This will help you understand how each adjustment affects the final product. ### Step 4: Establish Monitoring Set up your regular particle size testing schedule. Decide who will take samples, who will run the analysis, and who will review the results. Make sure everyone knows their role and has the training and equipment they need. Create a recordkeeping system, whether it is a paper log, a spreadsheet, or a software program. The system should be simple enough to maintain consistently but detailed enough to be useful for troubleshooting. ### Step 5: Review and Adjust Review your particle size data and performance metrics regularly, at least quarterly. Look for trends and identify any issues that need attention. Make adjustments as needed and document the changes you make. Over time, you will develop a feel for how your equipment behaves and what adjustments are needed under different conditions. This knowledge is valuable and will help you maintain optimal particle size with minimal effort. ## The Economics of Particle Size Management ### Feed Efficiency Savings The primary economic benefit of optimal particle size is improved feed efficiency. Moving from a coarse grind above 900 microns to 700 microns can improve feed conversion by 5 to 7 percent. On a farm feeding 10,000 pigs per year with an average feed conversion of 2.8 and feed costs of $200 per ton, this improvement could save $28,000 to $39,000 annually. These savings are significant enough to justify investment in particle size testing equipment and regular monitoring. A sieve set and shaker cost a few hundred dollars and can pay for themselves in the first batch of feed you optimize. ### Reduced Health Costs Preventing gastric ulcers through proper particle size management saves money in several ways. You avoid death losses from acute ulcers, which can be substantial if a severe outbreak occurs. You reduce the need for treatment and veterinary visits. And you avoid the performance penalty that comes with chronic, low-grade stomach irritation. The cost of ulcer prevention is essentially zero. Feeding at 650 to 750 microns instead of 500 microns does not cost more, it simply requires the discipline to set the mill correctly and verify the results. ### Equipment and Energy Costs There is also an energy cost to grinding. Finer grinding requires more energy, so there is a small incentive to avoid grinding finer than necessary. The energy savings from feeding at 700 microns instead of 500 microns are modest, typically 1 to 2 kilowatt-hours per ton of feed, but they add up over a year. Coarser grinding also reduces wear on hammers, screens, and rolls, extending the life of your equipment. This reduces maintenance costs and downtime. ### Cost of Particle Size Testing The direct cost of particle size testing is small. A sieve set and shaker cost a few hundred dollars, and the time to run a test is about 30 minutes. If you test monthly, the annual cost is minimal compared to the potential savings. If you prefer to send samples to a lab, the cost is typically $20 to $50 per sample. Even at this cost, regular testing is a good investment given the potential savings in feed efficiency. ## Advanced Considerations ### Particle Size and Feed Processing Particle size interacts with other feed processing techniques. For example, pelleting can improve feed efficiency and reduce dust, but the particle size of the mash before pelleting affects pellet quality and the final particle size of the feed. If you pellet feed, work with your feed mill to understand how grinding and pelleting interact. Similarly, the use of feed enzymes such as phytase and xylanase can be affected by particle size. These enzymes work on the surface of feed particles, so finer grinding can improve their effectiveness. However, enzymes are typically added as a coating on pellets or as a liquid spray, so the interaction is complex. ### Alternative Grains The particle size recommendations in this guide are based primarily on corn-based diets. If you feed other grains such as wheat, barley, sorghum, or oats, the optimal particle size may be different. These grains have different physical characteristics and digestibility profiles. Wheat and barley are more digestible than corn even at coarser particle sizes, so you may be able to feed them slightly coarser. Sorghum has a harder kernel and may need finer grinding for optimal digestibility. Work with a nutritionist to determine the best particle size for your specific grain mix. ### Particle Size and Mycotoxins Fine grinding can increase the risk of mycotoxin exposure because it releases more of the toxins from the grain matrix. If you are feeding grain that may be contaminated with mycotoxins, consider coarser grinding and more frequent testing for toxin levels. Mycotoxin contamination is a serious health risk for pigs, causing reduced feed intake, immune suppression, and reproductive problems. Particle size management cannot replace a comprehensive mycotoxin monitoring program. ## Frequently Asked Questions ### What is the ideal particle size for grow-finish pig feed? The ideal particle size for grow-finish pigs on corn-based diets is 650 to 750 microns. This range provides a good balance between digestibility and stomach health. Finer particles below 500 microns increase the risk of gastric ulcers, while coarser particles above 900 microns reduce feed efficiency. Within this range, you can adjust slightly based on your individual conditions, with pigs in the early grow phase benefiting from the finer end and finishing pigs doing well at the coarser end. ### How do I measure feed particle size on my farm? The standard method is dry sieve analysis using a 13-screen sieve set. Take a representative feed sample of about 100 grams, place it on the top screen of the stacked set, and shake for 10 minutes using a mechanical shaker. Weigh the feed retained on each screen and calculate the geometric mean particle size and geometric standard deviation. You can purchase a sieve set and shaker from agricultural supply companies, or you can send samples to a commercial lab for analysis. ### Can grinding feed too fine cause stomach ulcers in pigs? Yes, grinding feed too fine is a major cause of gastric ulcers in pigs. Fine particles create a fluid stomach content that does not form a protective mat at the top of the stomach. This allows acidic stomach juices to contact the unprotected esophageal region of the stomach lining, leading to inflammation and ulceration. Keeping particle size above 600 to 650 microns for grow-finish pigs is important for ulcer prevention. ### What is the difference between hammer mills and roller mills for pig feed? Hammer mills use rotating hammers to impact grain against a perforated screen, producing a wider range of particle sizes. Roller mills use counter-rotating rolls to crush grain, producing a more uniform grind with fewer fine particles. Roller mills generally produce feed with a lower geometric standard deviation, which is better for pig performance and stomach health. However, both types of mills can produce acceptable feed if properly adjusted and maintained. ### How often should I check my feed particle size? You should check particle size at least monthly for most operations. If you have recently changed equipment, ingredients, or mill settings, test more frequently until you confirm consistent results. Regular testing helps you catch equipment wear and other problems before they cost you money in reduced feed efficiency or increased stomach issues. ### Does particle size affect sows differently than growing pigs? Yes, sows should be fed coarser diets than growing pigs. A particle size of 700 to 900 microns is appropriate for gestating and lactating sows. The coarser grind helps maintain stomach health during the stress of gestation and lactation, and it may improve fiber utilization and gut health. Sows are often limit-fed, and coarser particles help them feel fuller between meals. ### What signs indicate that my feed particle size is wrong? Signs of overly fine feed include gastric ulcers, vomiting, reduced feed intake, high dust levels in the barn, and feed bridging in bins and feeders. Signs of overly coarse feed include poor feed conversion, visible whole grain in manure, and slower than expected growth. The most reliable way to know if particle size is wrong is to measure it directly using sieve analysis. ### Can I adjust particle size to improve feed efficiency without measuring? You can make educated guesses, but without measuring you cannot know if your adjustments are working. Particle size is affected by many factors including equipment wear, grain moisture, and mill settings. What worked last month may not work today. Regular measurement is the only reliable way to maintain optimal particle size and capture the feed efficiency benefits. ## Related Farming Guides This section will be populated with links to related farming guides on swine nutrition, feed management, and herd health topics. Check back for updates or explore the farming guides section of this site for more information. ## 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 - National Pork Board: https://www.pork.org/ - USDA APHIS Swine Health: https://www.aphis.usda.gov/livestock-poultry-disease/swine - FAO Pig Production: https://www.fao.org/pig-production-and-products/en/ - FAO Animal Production and Health: https://www.fao.org/animal-production/en/ - WOAH (World Organisation for Animal Health): https://www.woah.org/en/home/ > This article is educational and is not a substitute for veterinary diagnosis, treatment, public-health guidance, or regulatory reporting.