| Importance of grinding | Particle size | Problems with coarse grind | Problems with fine grind | Summary
Importance of Grinding
Feed costs represent 65 to 70 per cent of the variable cost of producing pigs. Therefore, optimum feed use and processing is critical for your economic profitability.
Grinding is the most important step in processing cereal grains for use in swine diets. Proper grinding provides several benefits:
- improves digestibility of energy and other nutrients by increasing surface area of ground particles
- as a result, feed efficiency is improved
- lower feed costs (per kilogram of gain)
- improves uniformity of the mix
- reduces amount of segregation of particles in mash diets fed to pigs
Particle Size
Particle size refers to the average diameter of individual particles of grain or feed, or simply the “feed’s fineness of grind.” Average particle size is generally expressed in microns: one micron equals one millionth of a metre. Both the average and the variation in particle size around the average are important.
The most important quality control measurement of grinding is particle size. Producers can improve feed efficiency and lower feed cost per kilogram of gain by managing particle size.
In corn diets, reducing average particle size from 1,200 to 400 microns, provides a 1 to 1.5 per cent improvement in feed efficiency for every 100 microns reduction.
Generally, the optimum feed particle size is around 700 microns with a possible range of 600 to 800 microns. Individual grains that make up the diet may need to be ground to 600 microns so that once mixed with soybean meal or canola meal, feed particle size is in the 600 to 800 micron range.
Several factors influence particle size:
- in the hammer mill – screen size, tip speed and condition of hammers and screen
- grain or pulse and its moisture content
- flow rate through the hammer mill
Problems With Coarse Grind
Particle sizes larger than 800 microns may cause a variety of problems, such as a reduction in feed efficiency. For every 100 microns above the 800 microns level, producers may lose $0.50 per pig sold due to reduced feed efficiency.
Problems With Fine Grind
Feeding particles with a size smaller than 600 microns might lead to the bridging of feed in bins and feeders as well as ulcers. Ulceration can be caused by a small particle size, but the sporadic lack of feed due to bridging might worsen ulceration.
Summary
Grinding and particle size are important to optimize feed efficiency and feed costs per unit of gain. Optimum average feed particle size is around 700 microns.
Particle size can be controlled by screen size, condition and number of hammers, flow rate and speed of the hammers.
Particle size, which is expressed in microns, should be evaluated as a routine feed processing quality control measure.
Ruurd T. Zijlstra – Feed Industry Research Chair
University of Alberta
Telephone: (780) 492-8593
E-mail: ruurd.zijlstra@ualberta.ca |