by Steve Pemberton, D.V.M., Vigortone Technical Service Support Veterinarian

Over the years, pork producers have become increasingly aware of the affect feed particle size has on profitability. Maintaining adequate feed particle size requires diligence. Feed processing equipment requires regular maintenance and adjustment to maintain desired particle size.

Kansas State University has been a proponent of testing samples of feed for average micron particle size for many years. From 1986 to 1992, KSU tested more than 2,500 samples of corn for average micron particle size. Only 21% of those samples fell within the recommended particle size of 600 to 800 microns. During an 18-month period, ending in November of 2001, KSU tested an additional 670 corn samples and found that almost 65% fell within the 600 to 800 micron range. Feed processors are improving their grind, but 35% of those samples were still not within the proper range. Many pigs are still being fed feed that is either too coarse or too fine.

Problems With Coarse Grind

Particle size larger than the recommended upper range of 800 microns may cause a variety of problems. KSU data suggests that for every 100 microns that the particle size is above the 800 level, producers loose $0.50 per pig fed from the reduced feed efficiency. For example, if the particle size is 1,000 microns, reducing the particle size to 800 microns will return $1.00 per pig through improved feed efficiency.

Large particles may also lead to other problems. Swine will tend to "sort out" large particles. These large particles accumulate in the trough of the feeder, where they become stale, wet and often moldy. Stale, moldy feed can produce mycotoxins, which often leads to reduced feed intake and poor growth in pigs.

Problems With Fine Grind

Feed particle size that is smaller than 600 microns may lead to severe problems. Finely ground feed tends to pack in feed bins, feed lines, and feeders, causing bridging or binding which leads to less feed intake per day. Feed that is bridged in a feed bin is a real challenge to remove.

Finely ground feed may also lead to ulcers in swine. Ulcers can cause slow growth and in severe cases can lead to death. Once the lining of the stomach becomes damaged, absorption of nutrients is reduced, and appetite is lowered.

How To Fix The Problem

Sample the ground corn or complete feed, and submit one-half pound in a sealed bag to a laboratory that can evaluate particle size. Evaluate the results by looking at both the average micron reading and the standard deviation (often noted as SGW on the report). The standard deviation is a measure of how much uniformity there is among the particle sizes in the sample. High SGW numbers (>2.3) indicate that the variability in particle size is too high. An SGW >2.6, indicates a serious problem with particle size variability.

Rotate and replace hammers in the hammer mill as necessary. Too high of a rpm in the mill may cause the grain to be shattered when it hits the screen. Shattering leads to some very fine particles and some very large particles. Adjust the roller mill roller to the proper distance from the blades, so that the spacing is even and consistent. Replace worn parts regularly to achieve desired particle size. Mill maintenance is the key element in maintaining a consistent particle size.

For more information, please call us at 1-800-553-1712 or email us at contactus@vigortone.com.  Dr. Pemberton can be reached at spemberton@vigortone.com.

Reference: Kansas State University. Swine Update. November 2001. Vol. 23, No.5