Particle Size and Pig Performance
In the past, there has been confusion regarding the optimum particle size
in swine diets. This was a result of broad generalizations classifying dietary
particle size. In the past, terms like fine, medium, and coarse were used to define
particle size. More precise methods for determining particle size have been
developed based on the mean geometric diameter of particles (measured in
microns) and the geometric mean standard deviation of the particles or their
distribution (ASAE 1973). These measurements allow for more precise definition
of particle size and allow us to make specific recommendations to optimize swine
performance. It is essential that producers understand the procedures used by
various analytical labs in particle size analysis and how these slight variances
might effect the interpretation of the results. Examples of these variations in
particle size analysis include: different number of screens (i.e., 6 vs 13), addition
of a flow agent, use of balls and brushes, and calculations used to determine
particle size.
In addition to different procedures to measure particle size, another factor
complicating the data available on the effects of particle size on pig performance
are the interactions between particle size and grain source as well as age of the
pig. Grain source will be a variable because of different sizes and shapes of
kernels. Therefore recommendations for screen sizes in hammer mills or roll
corrugations or gap settings will vary with different grains. As for interactions
among particle size and age of the pig, it appears the young pig does a better job
of chewing its feed than growing-finishing hogs. The greatest potential for fine
grinding to improve feed efficiency will be for finishing pigs. However, fine
grinding or rolling will improve feed efficiency regardless of age.
A study conducted at Kansas State University demonstrates the effects of
particle size on starter pig performance. In the study, 192 pigs (initial weight 6.8
to 8.1 kg) were fed either corn- or sorghum-based diets (Table 1). The grains
were either processed through a hammer mill equipped with an 3.2 mm (1/8-inch;
539 to 624 microns) or .3 mm (1/4-inch; 722 to 877 microns) screen.