When it comes to feed, particle size does matter and the finer the better. At least to a certain extent.

“You improve digestibility as you lower micron size,” says Mike Tokach, Kansas State University nutritionist.

“This leads to improved feed efficiency and in extreme cases increased growth rates for grow/finish pigs. In lactating sows, smaller particles can increase milk production.”

For every 100-micron decrease in particle size, it can improve feed efficiency by about 1.2 percent, says Tokach. If particle size is more than 1,000 microns you see a 0.2 to 0.4 reduction in feed efficiency, says Marcia Carlson Shannon, University of Missouri swine nutritionist.

“Pigs get better nutrient absorption with finer particles,” says Shannon. “They get better utilization, because the smaller feed particles have more contact with the intestinal mucosal surface, which can minimize excretion volume.” 

Of course, too much of a good thing can cause problems. Getting feed too fine can cause flow-ability problems, with feed bridging and sticking in feed lines.

“Bridging can leave animals without feed and lead to increased stress, fighting and herd-health concerns,” says Crystal Groesbeck, Kansas State University swine nutrition graduate student who recently studied particle size and flow-ability.

The health concerns are primarily that fine-ground feeds cause more gastric ulcers.

“The ulcers are attributable to when pigs go off feed. Fine-ground feeds are more likely to bridge or cause other out-of-feed events,” says Tokach. “Pigs get ulcers relatively easy, the key is how fast the pig can repair the ulcers. Pigs on fine-ground and pelleted diets repair ulcers much slower.”

Up to 80 percent of pigs will show some ulceration at slaughter, according to John Deen, DVM, University of Minnesota. In the last six to eight years, some herds have had to pull out 10 percent of the herd because of gastric ulcers, he notes. The general feeling is that gastric ulcers become a problem when feed is ground at about 700 microns or less.

There’s no definite consensus on the ideal micron size for feed. Generally, people think a range of 700 to 800 microns is acceptable, but there are other factors to consider.

“The key is the range of particle size,” says Shannon. “If the range is from 400 to 1,200 microns, the average may be 800 microns, but the huge variation will cause problems with the feed’s flow-ability. All of the fine feed will flow into the first pens, while the other end of the barn will get the much larger particles. You want to minimize variation to about 700 to 900 micron particle size.” (See chart.)

The biggest factor in changing your feed particle size is the feed-processing efficiency and the increased cost relative to the increased feed efficiency, says Shannon.

Particle size is dependent on your equipment, says Tokach. Some roller mills can grind feed  to 600 microns or less with no flow problems—usually—he says. Even if you have a hammer mill, 700 microns should be safe.  There are other equipment considerations as well.

“Probably the biggest flow issue is your feed-handling system’s design,” says Tokach. “If you have two-inch feed lines you’ll need much larger particle sizes, but if you have three-inch or four-inch feed lines, you can have smaller particles.”

Adding fat to your diets can compound flow-ability problems. The more fat you add, the larger particle size you will have to use to avoid problems.

“As you increase added fat you decrease flow-ability,” says Groesbeck. “Added fat has a similar effect on both hammer-mill and roller-mill-ground grain. Roller-mill-ground grain with 6 percent added fat had very similar flow-ability as hammer-mill-ground grain with no added fat.”

Managing whatever type of feeding equipment you have is critical. If you run a hammer mill you have to make sure to check and rotate the hammers, ensure there are no holes in the screens and replace worn screens. For a roller mill, you need to check the rolls, the differential, and regroove worn rolls. Also, if your feed particles are too large, you should look at your grinding time. Producers often get in a hurry and don’t spend enough time grinding feed, says Shannon.

“Feeder adjustment and management is critical,” says Tokach. “Some feeders can’t handle fine feeds, while others have no problem with small particle size, so you need to determine what works in your system.”

Most producers grind feed as fine as they can get it and still have it flow through their system. Tokach says some nutritionists recommend feed as fine as 300 to 500 microns, but that’s not really practical in meal diets,
because it won’t flow through the feeding system.

To make sure your feed is the right particle size, Shannon suggests checking the particle size of your grain at least once a year. The fall is the best time to check, once you get some new crop corn. A second check in the spring also would be a wise idea. The frequency of testing should increase as the amount of grain that you process increases. To have your feed checked, call university Extension personnel, talk to your feed mill or a testing lab. For example, any Missouri regional livestock specialist can take a grain or complete feed sample and do a quick particle size check using a simple method of a No. 14 test sieve. It wouldn’t necessarily require a special trip. Again, make sure the lab checks the variation in particle size, as well as the average particle size.

Making sure your particle size is fine enough can help you improve feed efficiency, and put dollars in your pocket. If feed is too fine, it won’t flow through your system, leaving your pigs without feed, which causes another set of problems. That’s why it’s important to revisit this management area at least once a year.